Patent Publication Number: US-2018048216-A1

Title: Motor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2016-159218, filed on Aug. 15, 2016, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     In recent years, there has been a demand for increasing the rotational speed of a motor. However, an increase in the rotational speed of a motor results in generation of an eddy current which generates heat in the motor. Accordingly, the motor is generally cooled by a cooling mechanism. 
     For example, a motor disclosed in Japanese Unexamined Patent Application Publication No. 2014-23387 has a structure in which a groove extending in the axial direction of a rotor is formed in a resin mold for fixing a coil that is inserted into a slot of the stator and oil is caused to flow through the groove to thereby cool the stator. 
     In the motor, not only the stator, but also the rotor may generate heat. Although the motor disclosed in Japanese Unexamined Patent Application Publication No. 2014-23387 can cool the stator, it is difficult to suitably supply oil to the rotor, which may make it difficult to sufficiently cool the rotor. 
     Even if the motor has a structure in which the rotor can be supplied with oil, an air between the rotor and the stator is caused to flow along the circumferential direction of the rotor due to the rotation of the rotor. As a result, the oil is scattered due to the flow of the air, which makes it difficult to suitably supply oil to the rotor. After all, it may be difficult to sufficiently cool the rotor. 
     SUMMARY 
     The present invention has been made in view of the above-mentioned problems and realizes a motor having an excellent capability of cooling a rotor. 
     A motor according to an aspect includes: a rotor having a cylindrical shape; and a stator disposed so as to surround an outer peripheral surface of the rotor. The stator includes: a stator core including a plurality of teeth radially arranged about a rotation axis of the rotor; and a stator coil inserted between each adjacent pair of the teeth. A flow channel for supplying a coolant to the outer peripheral surface of the rotor is formed within the teeth. A projection part is provided at a tip face of each of the teeth facing the outer peripheral surface of the rotor in such a manner that an interval between the tip face of each of the teeth and the outer peripheral surface of the rotor gradually decreases in a rotation direction of the rotor. 
     With this structure, a radial component of the rotor is generated in the flow of the air between the rotor and the stator, so that the coolant supplied between the rotor and the stator can be suitably supplied to the rotor. Therefore, the motor has an excellent capability of cooling a rotor. 
     In the motor described above, the projection part is preferably formed of a non-magnetic material. 
     With this structure, magnetic properties of the stator are not changed and thus have no adverse effect on the characteristics of the motor. 
     In the motor described above, the projection part preferably includes an inclined part that gradually is inclined toward the outer peripheral surface of the rotor in a rotation direction of the rotor. 
     With this structure, the radial component of the rotor is suitably generated in the flow of the air between the rotor and the stator, and an air resistance caused when the rotor is rotated can be suppressed. 
     In the motor described above, the motor is preferably a motor of a compressor for a fuel cell. 
     Since the motor of the compressor for the fuel cell has a high rotational speed, an eddy current is generated and the motor is more likely to generate heat. Therefore, the above-mentioned motor is suitably used. 
     The above and other objects, features and advantages of the present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view schematically showing a motor according to an embodiment; 
         FIG. 2  is a perspective view schematically showing a rotor in the motor of the embodiment and a stator mounted with a stator coil; 
         FIG. 3  is a perspective view schematically showing the rotor in the motor of the embodiment and the stator in which the illustration of the stator coil is omitted; 
         FIG. 4  is a plan view schematically showing a stator core of the stator in the motor of the embodiment; 
         FIG. 5  is a diagram schematically showing a first steel plate of the stator in the motor of the embodiment; 
         FIG. 6  is a diagram schematically showing a second steel plate of the stator in the motor of the embodiment; 
         FIG. 7  is an enlarged view of a part facing the rotor of the stator in the motor of the embodiment; and 
         FIG. 8  is a diagram for explaining a preferable slope of an inclined part at a projection part. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Specific embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the following embodiments. For clarity of explanation, the following description and the drawings are simplified as appropriate. 
       FIG. 1  is a sectional view schematically showing a motor according to this embodiment.  FIG. 2  is a perspective view schematically showing a rotor in the motor of this embodiment and a stator mounted with a stator coil.  FIG. 3  is a perspective view schematically showing the rotor in the motor of this embodiment and the stator in which the illustration of the stator coil is omitted. 
     Note that in  FIG. 2 , the illustration of the stator coil of the stator is simplified. In  FIGS. 2 and 3 , the illustration of stacked steel plates of the stator is simplified. In the following description, for clarity of explanation, an up-and-down direction and a right-and-left direction of the motor are defined as shown in  FIG. 1 . Note that in a normal use mode of the motor, the up-and-down direction of the motor coincides with the vertical direction, and the right-and-left direction of the motor coincides with the horizontal direction. However, these directions may be changed as appropriate depending on the use mode of the motor. 
     A motor  1  of this embodiment is suitably used as a motor of a compressor for a fuel cell (FC). As shown in  FIG. 1 , the motor  1  includes a housing  2 , a rotor  3 , a stator  4 , and a cooling mechanism  5 . Although the motor  1  of this embodiment is structured as a motor of a compressor for FC, the motor  1  can also be implemented by other types of motors. 
     The housing  2  includes a first accommodating part  2   a  that accommodates the rotor  3  and the stator  4 , an air intake port  2   b,  an exhaust port  2   c  through which an air supplied from the intake port  2   b  is exhausted, and a first flow channel  2   d  that communicates the intake port  2   b  with the exhaust port  2   c.    
     As shown in  FIGS. 1 to 3 , the rotor  3  has a cylindrical shape as a basic form, and includes a magnet  3   a,  a cylinder  3   b,  and end plates  3   c.  The magnet  3   a  is formed into a cylindrical shape in which a penetrating part extends in the right-and-left direction of the rotor  3 . The cylinder  3   h  is formed into a cylindrical shape in which a penetrating part extends in the right-and-left direction of the rotor  3 , and the magnet  3   a  is press-fit into the penetrating part of the cylinder  3   b  in such a manner that a compressive stress is imparted to the magnet  3   a.  Each end plate  3   c  includes a penetrating part which has an inside diameter substantially equal to that of the penetrating part of the magnet  3   a  and is fit into the penetrating part of the cylinder  3   b  in such a manner that the magnet  3   a  is sandwiched between the end plates  3   c  in the right-and-left direction of the magnet  3   a.    
     As shown in  FIG. 1 , a rotating shaft  6  extending in the right-and-left direction of the motor  1  is press-fit into the penetrating parts of the penetrating magnet  3   a  of the rotor  3  and the end plates  3   c.  Further, the rotor  3  is rotatably supported by the housing  2  through the rotating shaft  6  in a state where the rotor  3  is accommodated in the first accommodating part  2   a  of the housing  2 . 
     In this embodiment, spacers  7 , bearings  8 , and sealants  9  are provided on the rotating shaft  6  in such a manner that the rotor  3  is sandwiched in the right-and-left direction of the motor  1 , and the rotating shaft  6  is rotatably supported by the housing  2  through the bearings  8  and the sealants  9 . With this structure, the rotator  3  can he rotatably supported by the housing  2  through the rotating shaft  6 . 
     A right-side part of the rotating shaft  6  is provided with a resolver  10  for detecting a rotation angle of the rotor  3 . An axial force of a nut  11  that is screwed into a right end part of the rotating shaft  6  allows the rotor  3 , the right and left spacers  7 , the right and left hearings  8 , the sealants  9 , and the resolver  10  to be fastened between the nut  11  and a flange part  6   a  that is formed on the rotating shaft  6 , thereby allowing the rotor  3  and the rotating shaft  6  to be rotatably supported. In this embodiment, the resolver  10  is accommodated in the second accommodating part  2   e  that is formed in the housing  2 , but the arrangement of the resolver  10  is not particularly limited. 
     A left-side part (a part on the left side of the flange part  6   a  of the rotating shaft  6 ) of the rotating shaft  6  projects toward the first flow channel  2   d  of the housing  2 . A turbine  12  that is disposed in the first flow channel  2   d  of the housing  2  passes through the left-side part of the rotating shaft  6 , and a nut  13  is screwed into the left-side part of the rotating shaft  6  in such a manner that the turbine  12  is fixed between the nut  13  and the flange part  6   a  of the rotating shaft  6 . Accordingly, when the rotating shaft  6  is rotated, the air sucked from the intake port  2   b  of the housing  2  is compressed by the turbine  12  and exhausted from the exhaust port  2   c  of the housing  2 , and is then supplied to, for example, the FC stack. 
     As shown in  FIGS. 2 and 3 , the stator  4  is disposed so as to surround the rotor  3  and is fixed to the housing  2  in a state where the stator  4  is accommodated in the first accommodating part  2   a  of the housing  2 . 
     As shown in  FIG. 2 , the stator  4  includes a stator core  4   a  and a stator coil  4   b.  As shown in  FIGS. 1 and 3 , the stator core  4   a  is composed of a plurality of stacked steel plates  4   c,  and includes inserted parts  4   d,  teeth  4   e,  and slots  4   f.  Note that the detailed shape of each steel plate  4   c  is described later. 
     As shown in  FIG. 3 , each inserted part  4   d  is formed to so as to penetrate in the right-and-left direction of the stator  4  through a substantially central part of the stator  4  and the rotor  3  is inserted into the inserted part  4   d.  The teeth  4   e  are radially arranged about a rotation axis AX 1  ( FIG. 1 ) of the rotor  3  and each slot  4   f  is formed between each adjacent pair of the teeth  4   e.  The stator coil  4   b  is inserted into each slot  4   f  in such a manner that the stator coil  4   b  is wound around predetermined teeth  4   e,  and the stator coil  4   b  is resin-molded. However, the stator coil  4   b  need not necessarily be resin-molded. There is no need to wind the stator coil  4   b  around the teeth, as long as the stator coil  4   b  is mounted on the stator core  4   a.    
     The cooling mechanism  5  cools the rotor  3  and the stator  4 . As shown in  FIG. 1 , the cooling mechanism  5  of this embodiment includes a pump  5   a  and a cooler  5   b.  The pump  5   a  delivers the coolant accumulated in a receiving part  2   f,  which is formed below the first accommodating part  2   a  of the housing  2 , to the cooler  5   b.    
     Oil such as automatic transmission fluid (ATF) which is generally used for lubricating the bearings  8  is suitably used as the coolant. 
     The cooler  5   b  cools the coolant delivered from the pump  5   a  and supplies the coolant to a second flow channel  2   g  that is formed in the housing  2 . The second flow channel  2   g  is connected to each of a third flow channel  2   h  that guides the coolant to the bearings  8 , a fourth flow channel  2   i  that guides the coolant to the stator core  4   a  of the stator  4 , and a fifth flow channel  2   j  that guides the coolant to the stator coil  4   b  of the stator  4 . 
     With this structure, the coolant supplied to the second flow channel  2   g  is supplied (e.g., by dropping) to the bearings  8  through the third flow channel  2   h.  Further, the coolant supplied to the second flow channel  2   g  is supplied (e.g., by dropping) to the stator core  4   a  of the stator  4  through the fourth flow channel  2   i.  Furthermore, the coolant supplied to the second flow channel  2   g  is supplied (e.g., by dropping) to the stator coil  4   b  of the stator  4  through the fifth flow channel  2   j.    
     As a result, the bearings  8  and the stator core  4   a  and the stator coil  4   b  of the stator  4  can be cooled. Incidentally, the supplied coolant is collected into the receiving part  2   f  of the housing  2  and is delivered to the cooler  5   b  again by the pump  5   a.    
     In this case, the motor  1  of this embodiment has an excellent capability of cooling not only the stator  4 , but also the rotor  3 , and is capable of supplying a coolant to the rotor  3  through the stator  4 .  FIG. 4  is a plan view schematically showing the stator core of the rotor in the motor of this embodiment.  FIG. 5  is a diagram schematically showing a first steel plate of the stator in the motor of this embodiment.  FIG. 6  is a diagram schematically showing a second steel plate of the stator in the motor of this embodiment.  FIG. 7  is an enlarged view of a part facing the rotor of the stator in the motor of this embodiment.  FIG. 8  is a diagram for explaining a preferable slope of the inclined part of the projection part. 
     As shown in  FIG. 4 , the stator core  4   a  of the stator  4  of this embodiment includes a penetrating part  4   g  that penetrates in the up-and-down direction of the stator  4  and is formed at a location immediately below the fourth flow channel  2   i  of the housing  2 . The penetrating part  4   g  is disposed, for example, at substantially the center in the right-and-left direction and the front-back direction of the stator  4 . In order to form the penetrating part  4   g,  the first steel plate  4   h  and the second steel plate  4   i  are combined and used as the steel plate  4   c  of the stator core  4   a  in this embodiment. In this case, additional steel plates may be combined to form the stator core  4   a.  The arrangement of the through-hole  4   g  is not particularly limited as long as the through-hole  4   g  is formed in the stator core  4   a.    
     The first steel plate  4   h  is formed of a magnetic steel plate, and includes, for example, an annular part  4   j,  radial parts  4   k,  and fixed parts  41  as shown in  FIG. 5 . The annular part  4   j  is formed into, for example, a substantially annular shape as viewed along the right-and-left direction of the stator  4 . 
     The radial parts  4   k  constitute the teeth  4   e  of the stator  4 . For example, the width of each of the radial parts  4   k  gradually increases outward from the center of the annular part  4   j  as viewed along the right-and-left direction of the stator  4 . Tip ends of the radial parts  4   k  are arranged at intervals from the outer peripheral surface of the rotor  3  in the radial direction of the rotor  3 . A bottom part of each of the radial parts  4   k  is connected to the inner peripheral surface of the annular part  4   j.  Further, first notch parts  4   m  for forming the slots  4   f  between each adjacent pair of the radial parts  4   k  are provided. 
     Each fixed part  41  projects outward from the outer peripheral surface of the annular part  4   j  with respect to the center of the annular part  4   j,  and is fixed to the housing  2 . Each fixed part  41  includes a penetrating part  4   n  through which, for example, a bolt (not shown) for fixing the stator  4  to the housing  2  penetrates. 
     As shown in  FIG. 6 , the second steel plate  4   i  has substantially the same structure as that of the first steel plate  4   h,  and thus repeated descriptions are omitted. The second steel plate  4   i  includes a second notch part  4   o  for forming the penetrating part  4   g.  The second notch part  4   o  is formed so as to penetrate through the annular part  4   j  and the radial part  4   k.  One end of the second notch part  4   o  reaches the tip end of the corresponding radial part  4   k,  and the other end of the second notch part  4   o  reaches the outer peripheral surface of the annular part  4   j.  Further, the second notch part  4   o  extends in, for example, the up-and-down direction of the stator  4 . Instead, the second notch part  4   o  may he curved, may be formed in a zigzag shape, or may have parts with different widths. 
     When the second steel plates  4   i  are stacked to form a part where the penetrating part  4   g  of the stator core  4   a  is formed and the first steel plates  4   h  are stacked to form another part of the stator core  4   a,  the stator core  4   a  including the penetrating part  4   g  as shown in  FIG. 4  can be formed. The structure of the stator core  4   a  allows a part of the coolant supplied from the fourth flow channel  2   i  of the housing  2  to drop to the penetrating part  4   g  of the stator core  4   a  and supplied to the rotor  3  through the penetrating part  4   g.    
     Although not shown, bolts are inserted into the penetrating parts  4   n  of the fixed parts  41  of the stacked first steel plates  4   h  and second steel plates  41  and into a fixing jig formed on the housing  2 , and nuts are screwed onto the bolts, so that the stator  4  can be fixed to the housing  2 . However, the fixing means for fixing the stator  4  to the housing  2  is not limited to the above- mentioned fixing means and any fixing means may be used as long as the stator  4  can be fixed to the housing  2 . 
     In this case, since the rotor  3  is rotated, the air between the rotor  3  and the stator  4  flows along the circumferential direction of the rotor  3 . Accordingly, there is a possibility that the coolant supplied to the rotor  3  through the penetrating part  4   g  of the stator  4  may be scattered by the flow of the air and thus not suitably supplied to the rotor  3 . Therefore, the first steel plate  4   h  and the second steel plate  4   i  of this embodiment (i.e., the stator  4  of this embodiment) has a structure capable of generating a radial component (a component in the direction of the rotation axis AX 1 ) of the flow of the air between the rotor  3  and the stator  4 . 
     Specifically, as shown in  FIG. 7 , a tip end (i.e., a tip face of each of the teeth  4   e  of the stator core  4   a ) of each of the radial parts  4   k  of the first steel plate  4   h  and the second steel plate  4   i  is provided with a projection part  4   p  that is formed in such a manner that the interval between the tip end of each radial part  4   k  and the outer peripheral surface of the rotor  3  gradually decreases in a rotation direction R of the rotor  3 . The projection part  4   p  is disposed in a part or the entire area in the right-and-left direction of the stator  4 . 
     With this structure, the radial component of the rotor  3  is generated in the flow of the air between the rotor  3  and the stator  4 , and thus the coolant supplied to the rotor  3  through the penetrating part  4   g  of the stator core  4   a  can be suitably supplied to the rotor  3 . Accordingly, the motor  1  of this embodiment can be structured to have an excellent capability of cooling the rotor  3 . In addition, the coolant is supplied to the inserted part  4   d  of the stator core  4   a  by the circumferential component of the rotor  3  in the flow of the air between the rotor  3  and the stator  4 , thereby making it possible to suitably cool the stator  4 . 
     As shown in  FIG. 7 , the projection part  4   p  may include an inclined part  4   g  that is inclined in such a manner that, for example, the inclined part  4   g  gradually approaches the outer peripheral surface of the rotor  3  in the rotation direction R of the rotor  3 . With this structure, the radial component of the rotor  3  can be suitably generated in the flow of the air between the rotor  3  and the stator  4 , and the air resistance during the rotation of the rotor  3  can be suppressed. Therefore, a decrease in the output of the rotor  3  can be suppressed, 
     A preferable slope of the inclined part  4   q  of the projection part  4   p  will now be considered. For example, as shown in  FIG. 8 , when the radius of the rotor  3  is represented by “r” and the distance from the rotation axis AX 1  of the rotor  3  to the part where the projection part  4 P is not formed at the tip face of each of the teeth  4   e  of the stator core  4   a  is represented by “r+c”, the inclined part  4   q  is inclined in such a manner that the inclined part  4   q  gradually approaches the outer peripheral surface of the rotor  3  in the rotation direction R of the rotor  3  from the intersecting point between the tip face of the tooth  4   e  and a central line L 1  of the tooth  4   e.  As a coordinate system, xy coordinates with an origin at the rotation axis AX 1  of the rotor  3  as shown in  FIG. 8  are used. 
     The equation of the outer periphery of the rotor  3  is represented by the following &lt;Formula 1&gt;. 
         x   2   +y   2   =r   2    &lt;Formula 1&gt;
 
     The equation of a straight line L 2  extending on the inclined part  4   q  is represented by the throwing &lt;Formula 2&gt;. 
         y=ax+r+c    &lt;Formula 2&gt;
 
     An intersecting point between the straight line L 2  and the outer periphery of the rotor  3  is represented by the following &lt;Formula 3&gt;. 
         x   2 +( ax+r+c ) 2   =r   2    &lt;Formula 3&gt;
 
     In order for the straight line L 2  to contact the rotor  3  at the above-mentioned intersecting point, the discrimination of the solution to a quadratic equation for x in &lt;Formula 3&gt; satisfies the following &lt;Formula 4&gt;. 
       { a ( r+c )} 2 −( a   2 +1){( r+c ) 2   −r   2 }=0   &lt;Formula 4&gt;
 
     When a slope “a” is calculated from the &lt;Formula 4&gt; to obtain “a=tan θ”, a slope angle θ of the straight line L 2  when the straight line L 2  contacts the outer periphery of the rotor  3  is obtained. 
     The value of the slope angle is preferably larger than the slope angle θ of the straight line L 2  obtained from &lt;Formula 4&gt; so that the coolant can be actively supplied to the rotor  3 . For example, when r=29 mm and c=2 mm, the slope angle θ of the straight line L 2  is nearly equal to 28.5 deg. If the slope angle θ has a value larger than such a value, the coolant is more easily supplied to the rotor  3 . However, if the value of the slope angle θ of the straight line L 2  is extremely large, it is expected that the air resistance during the rotation of the rotor  3  increases. Therefore, the slope angle θ of the straight line L 2 , i.e., the slope angle θ of the inclined part  4   q  is preferably in a range from about 30 deg to 45 deg. 
     Note that the projection part  4   p  may have such a shape that the differential coefficient of the tip end of the projection part  4   p  that is located near the rotor  3  is larger than the slope of the tangent to the rotor  3  that passes through the tip end of the projection part  4   p  and thus the air resistance during the rotation of the rotor  3  can be suppressed. Therefore, the surface of the projection part  4   p  that faces the rotor  3  may have a curved shape or a step shape. The projection part  4   p  may be formed in a part or the entire area of the tip face of each of the teeth  4   e  of the stator core  4   a.    
     In this case, the projection part  4   p  may he formed of a non-magnetic material. For example, the projection part  4   p  may have a structure in which the projection part  4   p  is formed of a non-magnetic material such as austenite and the projection part  4   p  is formed at the tip face of each of the radial parts  4   k  of the first steel plate  4   h  or the second steel plate  4   i.  With this structure, the magnetic properties of the stator  4  are not changed and thus have no adverse effect on the characteristics of the motor. 
     Thus, the motor  1  of this embodiment has a structure in which the projection part  4   p  is provided at the tip face of each of the teeth  4   e  of the stator core  4   a  in such a manner that the interval between the tip face of each of the teeth  4   e  and the outer peripheral surface of the rotor  3  gradually decreases in the rotational direction of the rotor  3 . With this structure, the radial component of the rotor  3  can be generated in the flow of the air between the rotor  3  and the stator  4  and the coolant supplied to the rotor  3  through the penetrating part  4   g  of the stator  4   a  can be suitably supplied to the rotor  3 . Accordingly, the motor  1  of this embodiment can be structured to have an excellent capability of cooling the rotor  3 . In particular, since the rotational speed of a motor of a compressor for FC is, for example, 40,000 rpm, an eddy current is generated and thus the motor is more likely to generate heat. Therefore, the motor  1  of this embodiment is suitably used. 
     The present invention is not limited to the embodiments described above and can be modified as appropriate without departing from the scope of the invention. 
     For example, when the motor  1  is disposed in a mode in which it is difficult to drop the coolant to the penetrating part  4   g  of the stator  4 , the fourth flow channel  2   i  of the housing  2  and the penetrating part  42  of the stator  4  may he connected by a connecting pipe. In other words, the motor  1  is not limited to the mode shown in  FIG. 1 , but instead the motor  1  can he applied to, for example, a mode in which the right-and-left direction shown in  FIG. 1  coincides with the vertical direction. 
     For example, the motor  1  of this embodiment has a structure capable of cooling the stator coil  4   b  of the stator  4  and the bearings  8 . However, these cooling systems may be omitted. 
     From the invention thus described, it will be obvious that the embodiments of the invention may he varied in many ways. Such variations are not to he regarded as a departure from the spirit and scope of the invention, and all such modifications as would he obvious to one skilled in the art are intended for inclusion within the scope of the following claims.