Abstract:
Provided is a rotating electric machine the interior of which can be suitably cooled. A coolant supply means of the rotating electric machine supplies a cooling fluid to the bottom of a tubular member from a location closer to one end of a rotary shaft than the bottom, and the bottom of the tubular member is equipped with through-holes that run in the axial direction of the rotary shaft, with the cooling fluid being supplied to the interior of the tubular member through the through-holes.

Description:
TECHNICAL FIELD 
     The present invention relates to a rotary electric machine that makes it possible to cool the inside of the rotary electric machine. 
     BACKGROUND ART 
     According to Japanese Laid-Open Patent Publication No. 2003-324901 (hereinafter referred to as “JP 2003-324901 A”), several structures for cooling the inside of the rotary electric machine are disclosed (see FIGS. 1 through 11). In some of the disclosed structures, an oil coolant is supplied radially outward of the rotary electric machine from the inside thereof, such that an oil coolant is circulated through the inside of a shaft 28 (see FIGS. 7 and 8). 
     SUMMARY OF INVENTION 
     If the oil coolant is supplied to the inside of the rotary electric machine through the inside of the rotary shaft, as disclosed in FIGS. 7 and 8 of JP 2003-324901 A, the specifications of the coolant supply passage such as the number, position, and size of the holes are limited in view of the strength of the rotary shaft. Thus, there is still room for improvement in the technique, for cooling the inside of the rotary electric machine. 
     The present invention has been made in view of the aforementioned problem. An object of the present invention is to provide a rotary electric machine that can suitably cool the inside of the rotary electric machine. 
     According to the present invention, a rotary electric machine includes a motor rotor and a coolant supply unit configured to supply a cooling fluid for cooling the motor rotor. The motor rotor includes a rotational shaft, a tubular member having a bottom wall on one end side of the rotational shaft and an opening on another end side of the rotational shaft, the bottom wall being fixed to an outer circumferential surface of the rotational shaft, and a rotor core fixed to an outer circumferential surface of the tubular member. The coolant supply unit supplies the cooling fluid from the one end side of the rotational shaft with respect to the bottom wall of the tubular member, to the bottom wall of the tubular member. The bottom wall of the tubular member has a through hole extending along an axial direction of the rotational shaft. The cooling fluid is supplied through the through hole to inside of the tubular member. 
     According to the present invention, the cooling fluid is supplied to the bottom wall (outside) of the tubular member, and enters the tubular member through the through hole. Thus, it is possible to cool a member disposed in the tubular member or the rotor core fixed to the outer circumferential surface of the tubular member. 
     The tubular member has the opening remote from the bottom wall (on another end side of the rotational shaft). In this case, the cooling fluid, which is supplied to the inside of the tubular member from the side of the bottom wall, can be discharged from the tubular member through the opening. Therefore, the cooling fluid is prevented from entering an air gap between the motor rotor and the motor stator facing the motor rotor, and thus the rotational resistance of the rotary electric machine is prevented from being increased. 
     Further, the through hole for guiding the cooling fluid to the inside of the tubular member is formed in the bottom wall of the tubular member. Therefore, compared with the case in which the through hole is provided only in the rotational shaft, various routes can be provided for supplying the cooling fluid to the inside of the tubular member. Also, various specifications such as a flow rate or supply pressure of the cooling fluid can be set more flexibly, which are otherwise difficult to select due to the restriction of the specifications such as the dimension and strength of the rotational shaft when the through hole is to be formed in the rotational shaft, for example. 
     The annular protrusive wall may be formed on the bottom wall of the tubular member, and project toward the one end side of the rotational shaft from a portion positioned radially outward of the through hole. 
     In the above structure, the reservoir for the cooling fluid is formed radially inward of the protrusive wall under centrifugal forces that act on the cooling fluid during rotation of the motor rotor. The cooling fluid can be supplied from the reservoir through the through hole to the inside of the tubular member. Therefore, even if the supply pressure of the coolant supply unit is relatively small, the cooling fluid can be supplied through the through hole to the inside of the tubular member. As a result, when an electric pump is used as the coolant supply unit, the amount of workload by the electric pump can be reduced. 
     In a case a pump is mechanically coupled to the rotary electric machine and operates as the coolant supply unit by the drive force of the rotary electric machine, the supply amount or supply pressure of the cooling fluid tends to be small at the time of low-speed rotation of the rotary electric machine since the output of the pump is small. Even in such a case, because the cooling fluid can be pooled on the annular protrusive wall, an insufficient supply of the cooling fluid to the inside of the tubular member can be prevented by guiding the cooling fluid to the through hole easily. Stated otherwise, drive conditions such as the speed of rotation of the rotary electric machine have less effect on the supply amount of the cooling fluid by the pump. 
     The coolant supply unit may have an outlet hole on the one end side of the rotational shaft with respect to the bottom wall of the tubular member, the outlet hole configured to supply the cooling fluid toward the bottom wall of the tubular member, and the outlet hole may be disposed radially inward of the first protrusive wall and face the bottom wall of the tubular member in the axial direction. In this structure, the cooling fluid can be guided to the reservoir efficiently, since the cooling fluid, which is supplied toward the bottom wall of the tubular member, is guided to the reservoir formed radially inward of the protrusive wall by gravity. Further, the cooling fluid, which reaches the bottom wall of the tubular member radially inward of the protrusive wall from the outlet hole, is guided to the reservoir under centrifugal forces that act on the cooling fluid. Thus, the cooling fluid can be guided to the reservoir efficiently. 
     The coolant supply unit may include an axial flow passage formed in the rotational shaft, and an axial opening configured to establish communication between the axial flow passage and outside of the rotational shaft, and wherein the protrusive wall may have a portion that overlaps with the axial opening, as viewed along a radial direction of the motor rotor. In this structure, the cooling fluid, which overflows the axial flow passage, is guided to the reservoir formed radially inward of the protrusive wall under centrifugal forces or by gravity. Thus, the cooling fluid can be guided to the reservoir efficiently. 
     An inner circumferential surface of the protrusive wall may have a greater-diameter portion, which is progressively greater in diameter in a direction from the one end side to the other end side of the rotational shaft. In this structure, the greater-diameter portion can guide the cooling fluid from the one end side to the other end side of the rotational shaft under centrifugal forces that act on the cooling fluid during rotation of the motor rotor. Accordingly, the greater-diameter portion can enhance the movement of the cooling fluid in the tubular member, and thereby effectively cool the members such as the rotor core. 
     A rotor of a rotary sensor may be fixed to the protrusive wall. Therefore, the protrusive wall functions both to provide the reservoir for the cooling fluid, and to retain the rotor of the rotary sensor. Consequently, the rotary electric machine can be simpler in structure than if a member for retaining the rotor were provided separately from the protrusive wall. 
     A gear mechanism, which is coupled to the rotational shaft, may be disposed in the tubular member. In the above structure, by disposing the gear mechanism in the tubular member, it is possible to reduce the dimension of the rotary electric machine along the axial direction. Further, in addition to cooling the rotor core, it also is possible to cool or lubricate the gear mechanism (assuming that the cooling fluid doubles as a lubricating oil). Therefore, as opposed to providing the cooling structure for the rotor core and the cooling structure for the gear mechanism separately from each other, the structure can be made simpler. 
     A second protrusive wall may be formed on the bottom wall of the tubular member and project toward the other end side of the rotational shaft from a portion positioned radially outward of the through hole, and a distal end of the second protrusive wall may overlap with a portion of a gear of the gear mechanism, as viewed along the radial direction of the motor rotor. In the above structure, the cooling fluid, which scatters under centrifugal forces radially, is guided to the gear of the gear mechanism, and can be used to cool or lubricate the gear (assuming that the cooling fluid doubles as a lubricating oil). Thereafter, the cooling fluid, which has been used to cool or lubricate the gear, further moves under centrifugal forces radially. When the cooling fluid reaches an inner circumferential surface of the tubular member, the cooling fluid can also cool the rotor core. 
     A frictional engagement unit, which is coupled to the rotational shaft, may be disposed in the tubular member. In the above structure, by disposing the frictional engagement unit (e.g., clutch mechanism) in the tubular member, it is possible to reduce the dimension of the rotary electric machine along the axial direction. Further, in addition to cooling the rotor core, it also is possible to cool or lubricate the frictional engagement unit (assuming that the cooling fluid doubles as a lubricating oil). Therefore, as opposed to providing the cooling structure for the rotor core and the cooling structure for the frictional engagement unit separately from each other, the structure can be made simpler. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a fragmentary cross-sectional view of a vehicle, especially a cooling system thereof, in which there is incorporated a motor that serves as a rotary electric machine according to an embodiment of the present invention; 
         FIG. 2  is an enlarged fragmentary cross-sectional view showing flows of an oil coolant in the motor; 
         FIG. 3  is a perspective view of a side cover that functions as a portion of the cooling system; and 
         FIG. 4  is a plan view, which is illustrated in a simplified form, showing the positions of through holes in a motor rotor. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A. Embodiment 
     1. Description of Overall Arrangement 
     1-1. Overall Arrangement 
       FIG. 1  is a fragmentary cross-sectional view of a vehicle  10 , especially a cooling system (coolant supply unit) thereof, which incorporates a motor  12  as a rotary electric machine according to an embodiment of the present invention.  FIG. 2  is an enlarged fragmentary cross-sectional view showing flows of an oil coolant  42  in the motor  12 . In  FIG. 2 , the thick arrows represent flows of the oil coolant  42 . It should be noted that, for facilitating understanding of the present invention,  FIGS. 1 and 2  are cross-sectional views taken along line I-I of  FIG. 4 , to be described later. Further, a side cover  30  (to be described later) in  FIGS. 1 and 2  is shown in cross section (taken along line I-I of  FIG. 3 ) through all of an inlet hole  32  and first through third outlet holes  36 ,  38 ,  40 , to be described later (see  FIG. 3 ). 
     As shown in  FIG. 1 , the vehicle  10  has a speed reducer  14 , which serves as a gear mechanism, in addition to the motor  12 . A portion of the speed reducer  14  is disposed in the motor  12 . 
     The motor  12  serves as a drive source for generating a drive force F for the vehicle  10 . The motor  12  comprises a three-phase AC brushless motor for generating the drive force F for the vehicle  10  based on electric power supplied from a non-illustrated battery through a non-illustrated inverter. The motor  12  also regenerates electric power (regenerative electric power Preg) [W] in a regenerative mode, and outputs the regenerative electric power Preg to the battery in order to charge the battery. The regenerative electric power Preg may be output to a 12-volt system or a non-illustrated accessory device. 
     As shown in  FIGS. 1 and 2 , the motor  12  has a motor rotor  20  (hereinafter also referred to as a “rotor  20 ”), a motor stator  22  (hereinafter also referred to as a “stator  22 ”), a resolver rotor  24 , a resolver stator  26 , a motor housing  28 , and the side cover  30 . The resolver rotor  24  and the resolver stator  26  jointly make up a resolver  31 . 
     1-2. Cooling System 
     1-2-1. Side Cover  30   
       FIG. 3  is a perspective view of the side cover  30 , which functions as a portion of the cooling system. As shown in  FIGS. 1 through 3 , the side cover  30  has a single inlet hole  32 , a flow passage  34 , a single first outlet hole  36 , a single second outlet hole  38 , and a plurality of third outlet holes  40 . The first through third outlet holes  36 ,  38 ,  40  are supplied with an oil coolant  42  from a non-illustrated pump, which may be an electric pump or a mechanical pump. 
     As shown in  FIGS. 1 through 3 , according to the present embodiment, the oil coolant  42  is ejected or discharged from the side cover  30  toward the rotor  20  and the stator  22 . 
     More specifically, the first outlet hole  36  ejects or discharges the oil coolant  42  primarily toward a rotational shaft  50  of the rotor  20 . The second outlet hole  38  ejects or discharges the oil coolant  42  primarily toward a tubular member  52  of the rotor  20 . The third outlet hole  40  ejects or discharges the oil coolant  42  primarily toward the stator  22 . Each of the outlet holes  36 ,  38 ,  40  is in the form of a nozzle for ejecting or discharging the oil coolant  42 . 
     1-2-2. Motor Rotor  20   
     1-2-2-1. Rotational Shaft  50   
     As shown in  FIGS. 1 and 2 , the rotational shaft  50  of the rotor  20  has an axial opening  53  for supplying the oil coolant  42  to the inside of the rotational shaft  50 , a single first axial flow passage  54  that extends along axial directions X1, X2 (see  FIG. 1 ), and a plurality of second axial flow passages  56 , which establish fluid communication along radial directions R1, R2 (see  FIG. 4 ) of the motor  12  between the first axial flow passage  54  and the outside of the rotational shaft  50 . 
     The oil coolant  42 , which is supplied from the first outlet hole  36  of the side cover  30 , is guided through the first axial flow passage  54  into the second axial flow passages  56 , and then is discharged through the second axial flow passages  56  from the rotational shaft  50 . The discharged oil coolant  42  is supplied to the inside of the rotor  20  or to a portion of the speed reducer  14 . 
     1-2-2-2. Tubular Member  52   
     1-2-2-2-1. General 
     As shown in  FIG. 2 , etc., the rotor  20  has, in addition to the rotational shaft  50 , a bottomed tubular member  52 , a rotor core  60 , and a rotor yoke  62 . 
     The tubular member  52  includes a bottom wall  70  fixed to the outer circumferential surface of the rotational shaft  50  near the side cover  30 , and a side wall  72  that extends in the axial direction X2 from the outer edge of the bottom wall  70 . The side wall  72  opens remotely from the bottom wall  70 , i.e., the side wall  72  has an opening  74  remote from the bottom wall  70 . The speed reducer  14  has a planet gear  76  disposed in the tubular member  52 . 
     1-2-2-2-2. Bottom Wall  70   
     As shown in  FIG. 2 , the bottom wall  70  includes a base  80 , a first protrusive wall  82 , and a second protrusive wall  84 . The base  80  extends from the rotational shaft  50  along the radial direction R1. The base  80  has a plurality of through holes  86  defined in a portion thereof. The through holes  86  extend along the axial directions X1, X2 through the bottom wall  70  (base  80 ). 
       FIG. 4  is a plan view showing the positions of the through holes  86  in the motor rotor  20 , which is illustrated in a simplified form. As shown in  FIG. 4 , according to the present embodiment, there are four through holes  86 , which are spaced at equal intervals. The oil coolant  42 , which is ejected from the side cover  30  toward the bottom wall  70 , is supplied through the through holes  86  to the inside of the tubular member  52 . 
     The first protrusive wall  82  projects toward the side cover  30  (along the direction X1) from a portion positioned radially outward (along the direction R1) of the through holes  86 . The first protrusive wall  82  has an annular shape. For this reason, if the oil coolant  42 , which is ejected or discharged from the side cover  30  toward the bottom wall  70  during rotation of the rotor  20 , does not enter the through holes  86  directly, then the oil coolant  42  remains in an inner circumferential region of the first protrusive wall  82 , i.e., a region surrounded by the base  80  and the first protrusive wall  82 , under centrifugal forces that act on the oil coolant  42 . Stated otherwise, the base  80  and the first protrusive wall  82  jointly provide a reservoir  88  for the oil coolant  42 . Therefore, even if the oil coolant  42  does not enter the through holes  86  directly, the oil coolant  42  remains in the reservoir  88  and thereafter is supplied through the through holes  86  to the inside of the tubular member  52 . 
     The first protrusive wall  82  has a portion that overlaps with the axial opening  53  of the rotational shaft  50 , as viewed along the radial directions R1, R2 of the rotor  20 . Therefore, the oil coolant  42 , which overflows the first axial flow passage  54  through the axial opening  53 , remains in the inner circumferential region of the first protrusive wall  82  under centrifugal forces or by gravity, and thereafter, the oil coolant  42  is supplied through the through holes  86  to the inside of the tubular member  52  (see  FIG. 2 ). Consequently, the oil coolant  42 , which flows over the first axial flow passage  54  through the axial opening  53 , can be used to cool the rotor core  60  efficiently. 
     In addition, as shown in  FIG. 2 , the first protrusive wall  82  has a greater-diameter portion  90 , which is progressively greater in diameter in a direction from the side cover  30  toward the base  80  of the bottom wall  70 , i.e., in the direction X2. The greater-diameter portion  90  makes it easy for the reservoir  88  to be formed radially inward of the first protrusive wall  82 , i.e., in the direction R2, thereby minimizing the amount of oil coolant  42  that does not enter into the tubular member  52  after being supplied radially inward of the first protrusive wall  82 , i.e., in the direction R2. In  FIG. 2 , the first protrusive wall  82  is shown as being increased in diameter in both radial inward and radial outward directions. However, even if the first protrusive wall  82  is increased in diameter in the radial inward direction only, the first protrusive wall  82  is capable of operating in the aforementioned manner to offer the advantages described above. 
     The resolver rotor  24 , i.e., the rotor of a rotary sensor, is fixed to a radial outer surface of the first protrusive wall  82 , i.e., a surface thereof that faces in the direction R1. Therefore, the first protrusive wall  82  functions both to provide the reservoir  88  for the oil coolant  42 , and to retain the resolver rotor  24 . Consequently, the motor  12  can be simpler in structure than if a member for retaining the resolver rotor  24  were provided separately from the first protrusive wall  82 . 
     As shown in  FIG. 2 , the second protrusive wall  84  projects toward the opening  74  (along the direction X2 in  FIG. 2 ) from a portion positioned radially outward (along the direction R1) of the through holes  86 . The second protrusive wall  84  has an annular shape. A distal end of the second protrusive wall  84  overlaps with a portion of the planet gear  76 , as viewed along a radial outward direction of the rotor  20  (along the direction R1). Therefore, the oil coolant  42 , which is guided by the second protrusive wall  84 , is supplied to a portion of the planet gear  76  when the oil coolant  42  is discharged under centrifugal forces in a radial outward direction (along the direction R1). 
     1-2-2-2-3. Side Wall  72   
     As shown in  FIGS. 1 and 2 , the rotor core  60  and the rotor yoke  62  are fixed to a radial outer surface (which faces in the direction R1) of the side wall  72  of the tubular member  52 . As described above, the oil coolant  42  is supplied from the side cover  30  to the inside of the tubular member  52  through the rotational shaft  50  or the bottom wall  70  of the tubular member  52 . Thereafter, as the oil coolant  42  moves along the side wall  72  while the rotor  20  rotates, the oil coolant  42  cools the rotor core  60 . 
     The oil coolant  42 , which has reached the side wall  72 , moves along the side wall  72  into the opening  74  from which the oil coolant  42  is discharged. Thereafter, the oil coolant  42 , which is discharged from the opening  74 , is pooled on the bottom (not shown) of the motor housing  28 , whereupon the oil coolant  42  is ejected or discharged again from the side cover  30  toward the rotor  20  or the stator  22  by the pump. Heat from the oil coolant  42  may undergo heat transfer by a cooler or a warmer, not shown, before the oil coolant  42  is ejected or discharged again. 
     1-2-3. Motor Stator  22   
     The oil coolant  42 , which is supplied from the third outlet holes  40  of the side cover  30 , passes through the stator  22  while cooling various parts of the stator  22 , and drops onto the bottom of the motor housing  28 . 
     As shown in  FIG. 2 , etc., the resolver stator  26  is disposed on the motor stator  22  radially outward of the resolver rotor  24  along the direction R1. The resolver stator  26  produces an output signal depending on the rotational angle of the resolver rotor  24 . Therefore, the resolver  31  is capable of detecting the rotational angle of the motor rotor  20 . 
     2. Advantages of the Present Embodiment 
     According to the present embodiment, as described above, the oil coolant  42  is supplied to the bottom wall  70  (outside) of the tubular member  52 , and enters the tubular member  52  through the through holes  86 . Thus, it is possible to cool a member (planet gear  76 ) disposed in the tubular member  52  or the rotor core  60  fixed to the outer circumferential surface of the tubular member  52 . 
     The tubular member  52  has the opening  74  remote from the bottom wall  70  (on another end side of the rotational shaft  50 ). In this case, the oil coolant  42 , which is supplied to the inside of the tubular member  52  from the side of the bottom wall  70 , can be discharged from the tubular member  52  through the opening  74 . Therefore, the oil coolant  42  is prevented from entering an air gap between the motor rotor  20  and the motor stator  22  facing the motor rotor  20 , and thus the rotational resistance of the motor  12  is prevented from being increased. 
     Further, the through holes  86  for guiding the oil coolant  42  to the inside of the tubular member  52  are formed in the bottom wall  70  of the tubular member  52 . Therefore, compared with the case in which the through holes  86  are provided only in the rotational shaft  50 , various routes can be provided for supplying the oil coolant  42  to the inside of the tubular member  52 . Also, when through holes (first axial flow passage  54  and second axial flow passages  56 ) are to be formed in the rotational shaft  50 , for example, various specifications such as a flow rate or supply pressure of the oil coolant  42  can be set more flexibly, which are otherwise difficult to select due to the restriction of the specifications such as the dimension and strength of the rotational shaft  50 . 
     In the present embodiment, the annular first protrusive wall  82  is formed on the bottom wall  70  of the tubular member  52 , and projects toward (along the direction X1) one end side of the rotational shaft  50  from a portion positioned radially outward (along the direction R1) of the through holes  86 . 
     In the above structure, the reservoir  88  for the oil coolant  42  is formed radially inward, i.e., in the direction R2 of the first protrusive wall  82  under centrifugal forces that act on the oil coolant  42  during rotation of the rotor  20 . The oil coolant  42  can be supplied from the reservoir  88  through the through holes  86  to the inside of the tubular member  52 . Therefore, even if the supply pressure of an electric pump as a coolant supply unit is relatively small, the oil coolant  42  can be supplied through the through holes  86  to the inside of the tubular member  52 . As a result, the amount of workload by the electric pump can be reduced. 
     In a case a pump is mechanically coupled to the motor  12  and operates as the coolant supply unit by the drive force of the motor  12 , the supply amount or supply pressure of the oil coolant  42  tends to be small at the time of low-speed rotation of the motor  12  since the output of the pump is small. Even in such a case, because the oil coolant  42  can be pooled on the annular first protrusive wall  82 , a short supply of the oil coolant  42  to the inside of the tubular member  52  can be prevented by guiding the oil coolant  42  to the through holes  86  easily. Stated otherwise, drive conditions such as the speed of rotation of the motor  12  have less effect on the supply amount of the oil coolant  42  by the pump. 
     In the present embodiment, the side cover  30  has the second outlet hole  38  for supplying the oil coolant  42  to the bottom wall  70 , on one side (on the left in  FIG. 2 ) of the rotational shaft  50  with respect to the bottom wall  70  of the tubular member  52 . The second outlet hole  38  is disposed radially inward (along the direction R2) of the first protrusive wall  82  and faces the bottom wall  70  in the axial direction X2. In this structure, the oil coolant  42  can be guided to the reservoir  88  efficiently, since the oil coolant  42 , which is ejected or discharged toward the bottom wall  70  of the tubular member  52 , is guided to the reservoir  88  formed radially inward, i.e., in the direction R2 of the first protrusive wall  82  by gravity. Further, the oil coolant  42 , which reaches the bottom wall  70  of the tubular member  52  radially inward of the first protrusive wall  82  (along the direction R2) from the second outlet hole  38 , is guided to the reservoir  88  under centrifugal forces that act on the oil coolant  42 . Thus, the oil coolant  42  can be guided to the reservoir  88  efficiently. 
     In the present embodiment, the rotational shaft  50  has the first axial flow passage  54  and the axial opening  53  which establishes communication between the first axial flow passage  54  and the outside of the rotational shaft  50 . The first protrusive wall  82  has a portion that overlaps with the axial opening  53 , as viewed along the radial directions R1, R2 of the rotor  20  (see  FIG. 2 ). In this structure, the oil coolant  42 , which overflows the first axial flow passage  54 , is guided to the reservoir  88  formed radially inward, i.e., in the direction R2 of the first protrusive wall  82  under centrifugal forces or by gravity. Thus, the oil coolant  42  can be guided to the reservoir  88  efficiently. 
     In the present embodiment, an inner circumferential surface of the first protrusive wall  82  facing in the direction R2 has the greater-diameter portion  90 , which is progressively greater in diameter in a direction from the one end side of the rotational shaft  50  (on the left in  FIG. 2 ) to the other end side thereof (on the right in  FIG. 2 ). In this structure, the greater-diameter portion  90  can guide the oil coolant  42  from the one end side to the other end side of the rotational shaft  50  under centrifugal forces that act on the oil coolant  42  during rotation of the rotor  20 . Accordingly, the greater-diameter portion  90  can enhance the movement of the oil coolant  42  in the tubular member  52 , and thereby effectively cool the members such as the rotor core  60 . 
     The resolver rotor  24  is fixed to the first protrusive wall  82  according to the present embodiment. Therefore, the first protrusive wall  82  functions both to provide the reservoir  88  for the oil coolant  42 , and to retain the resolver rotor  24 . Consequently, the motor  12  can be simpler in structure than if a member for retaining the resolver rotor  24  were provided separately from the first protrusive wall  82 . 
     The planet gear  76  (gear mechanism), which is coupled to the rotational shaft  50 , is disposed in the tubular member  52  according to the present embodiment (see  FIGS. 1 and 2 ). In the above structure, by disposing the planet gear  76  in the tubular member  52 , it is possible to reduce the dimension of the motor  12  along the axial directions X1, X2. Further, in addition to cooling the rotor core  60 , it also is possible to cool or lubricate the planet gear  76 . Therefore, as opposed to providing the cooling structure for the rotor core  60  and the cooling structure for the planet gear  76  separately from each other, the structure can be made simpler. 
     In the present embodiment, the second protrusive wall  84  is formed on the bottom wall  70  of the tubular member  52  and projects toward the other end side of the rotational shaft  50  (along the direction X2) radially outward of the through holes  86  along the direction R1. The distal end of the second protrusive wall  84  overlaps with a portion of the planet gear  76 , as viewed in the radial directions R1, R2 (see  FIG. 2 ). 
     In the above structure, the oil coolant  42 , which scatters under centrifugal forces radially outward along the direction R1, is guided to the planet gear  76 , and can be used to cool or lubricate the planet gear  76 . Thereafter, the oil coolant  42 , which has been used to cool or lubricate the planet gear  76 , further moves under centrifugal forces radially outward along the direction R1. When the oil coolant  42  reaches an inner circumferential surface of the tubular member  52 , the oil coolant  42  can also cool the rotor core  60 . 
     B. Modifications 
     The present invention is not limited to the above embodiment, but various other arrangements may be employed based on the disclosed content of the present description. For example, the present invention can employ the following arrangements. 
     1. Objects to which the Present Invention is Applicable 
     In the above embodiment, the motor  12  is mounted on the vehicle  10 . However, the present invention is applicable to other situations in which the motor  12  may be employed. For example, although the motor  12  is used to propel the vehicle  10  in the above embodiment, the motor  12  may be used in other applications in the vehicle  10  (e.g., an electric power steering system, an air conditioner, an air compressor, etc.). Alternatively, the motor  12  may be used on industrial machines, home electric appliances, etc. 
     2. Motor  12   
     In the above embodiment, the motor  12  is a three-phase AC motor. However, the motor  12  may be another type of AC motor or a DC motor, for example, which is cooled by a cooling fluid, or which is of a reduced size. In the above embodiment, the motor  12  comprises a brushless motor. However, the motor  12  may be a brush motor. In the above embodiment, the motor stator  22  is disposed radially outward (along the direction R1) of the motor rotor  20  (see  FIG. 1 , etc.). However, the motor stator  22  may be disposed radially inward of the motor rotor  20 . 
     3. Resolver  31   
     In the above embodiment, the resolver rotor  24  is mounted on the first protrusive wall  82 . However, the resolver rotor  24  may be fixed to another member other than the first protrusive wall  82 , insofar as the oil coolant  42  is capable of being supplied from the bottom wall  70  of the tubular member  52  to the inside of the tubular member  52 , or in view of the structure of the electric power system. 
     4. Cooling System 
     4-1. Cooling Fluid 
     In the above embodiment, the oil coolant  42  is used as a cooling fluid. However, rather than the oil coolant  42 , another cooling fluid (e.g., water or the like) may be used from the standpoint of effecting the cooling function. However, in this case, potentially, the other cooling fluid may not be used as a lubricant for lubricating the gear mechanisms such as the planet gear  76 , etc. 
     4-2. Tubular Member  52   
     In the above embodiment, the planet gear  76 , which is coupled to the rotational shaft  50 , is disposed in the tubular member  52 . However, a different type of gear mechanism may be disposed in the tubular member  52 . Alternatively, other members may be disposed in the tubular member  52  that are cooled by the cooling medium. For example, a frictional engagement unit (clutch mechanism) (not shown), which is coupled to the rotational shaft  50 , may be disposed in the tubular member  52 , instead of the speed reducer  14  (planet gear  76 ). 
     By disposing a frictional engagement unit in the tubular member  52 , it is possible to reduce the dimension of the motor  12  along the axial directions X1, X2. Further, in addition to cooling the rotor core  60 , it also is possible to cool or lubricate the frictional engagement unit (assuming that the cooling fluid doubles as a lubricating oil). Therefore, as opposed to providing the cooling structure for the rotor core  60  and the cooling structure for the frictional engagement unit separately from each other, the structure can be made simpler.