Patent Publication Number: US-2013229072-A1

Title: Cooling Structure for Cooling Electric Motor for Vehicle

Description:
TECHNICAL FIELD 
     The present invention relates to a cooling structure for cooling an electric motor in an electric vehicle such as an electric car, an electric motorcycle, and a hybrid car. 
     BACKGROUND ART 
     In recent years, with a growing interest in the environment and from the prospect of depletion of oil resources in the future, it is more highly demanded than before to reduce fuel consumption in an automobile, an electric motorcycle, etc. On the one hand, there has been fast progress in the research and development of secondary cells represented by a lithium ion cell, and attempts to use electricity as a power source for driving the electric car or the hybrid car become highly popular. 
     Generally an electric motor has quite high energy efficiency as compared with an internal-combustion engine, but it generates heat during its operation. A leading cause of the heat is generation of heat (so-called copper loss) from a coil attributable to resistance of an electrical current flowing through windings. This increases temperature of the coil, resulting in an increase in the electrical resistance of the windings and a decrease in efficiency. The increased electrical resistance leads to generation of heat again, falling in a vicious cycle of the generation of heat, the rise in temperature, and the increase in electrical resistance. This becomes an obstacle to improving the output of the motor. 
     For this reason, from the past, various cooling structures have been proposed to effectively cool the electric motor in an electric vehicle. For example, Patent Document 1 discloses a technology which water-cools a case member of a motor and directly cools an exothermic portion of the motor using cooling oil, such as ATF, stored in the case member. According to this technology, a coil wound around a core part of a stator is produced by resin molding, and an oil path of the cooling oil is provided near a coil end which easily becomes a high temperature. 
     A portion of the winding of the coil end is exposed to this oil path, so that it is effectively cooled by the cooling oil. By supplying the cooling oil pumped up by a pump or the like to the oil path from above and squeezing out the cooling oil discharged from an outlet disposed at a lower end of the oil path by shaping the outlet like an orifice, the whole oil path becomes filled with the cooling oil and the winding of the coil is immersed. 
     On the one hand, Patent Document 2 discloses a cooling structure in which an oil path of cooling oil is provide between a coil end of a stator and a coil end cover in an electric motor in order to directly cool the coil end using a coolant like in the above-mentioned technology, and the coolant is allowed to leak from the oil path so as to fill up a minute gap between the coil end cover and a case member of a motor. With this configuration, thermal resistance between the coil end cover and the case member of the motor decreases, and the cooling efficiency increases. 
     In addition, for example, Patent Document 3 discloses a motor configured such that cooling oil, such as ATF and gear oil, is sprayed onto a coil end of a stator so that the coil end can be cooled. In this configuration, the cooling oil is sprayed onto the coil end of the stator in a manner that the cooling oil is first introduced into a hollow portion formed near an end plate of a rotor via an oil path in a shaft, and then the cooling oil is ejected from an ejection hole communicating with the hollow portion by centrifugal force generated by rotation of the rotor. 
     Furthermore, arrangement of the ejection hole is set in consideration of the fact that the orbit or ejecting force of the ejected cooling oil changes according to the centrifugal force which changes according to a rotation speed of the rotor so that the cooling oil may be sprayed onto the coil end of the stator in a state of being stabilized as uniformly as possible. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2006-197772 
     Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2009-118667 
     Patent Document 3: Japanese Patent Application Laid-Open Publication No. 2009-273285 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, when the oil path is provided in the resin-molded body with which the coil of the core portion of the stator is molded together or when the oil path is provided between the coil end and the coil end cover as described in the above-described conventional examples (Patent Documents 1 and 2), a production man hour or the number of parts is increased, resulting in a cost hike. 
     When the winding becomes a high temperature in the state in which it is immersed in the cooling oil in the oil path, there is a problem that deterioration of the covering occurs and mechanical strength and dielectric strength of the covering decrease. In this regard, according to the technology of Patent Document 1, under the condition of a small heat load, control is performed such that an amount of a coolant supplied to the oil path is reduced to prevent the winding from being immersed in the coolant. However, this control causes a further cost hike. 
     On the other hand, when the cooling oil is sprayed onto the coil end like in the latter conventional example (Patent Document 3), the structure can be comparatively simplified. However, when the coolant is ejected from the rotor rotating at high speed, it is not easy to precisely spray the coolant ejected from it onto the coil end as intended no matter how hard the study is made on the arrangement of the ejection hole. Furthermore, there is a risk that the cooling oil which rebounds after being sprayed onto the coil end is likely to invade a gap between the rotor and the stator, and if this occurs, rotation resistance increases. 
     Yet furthermore, since an oil sac and/or a feed oil path of the cooling oil are provided in the rotor rotating at high speed and even the ejection hole is provided in the rotor, when taking rotational balance, an oscillation characteristic, etc. of the rotor into consideration, considerable precision in processing and assembly is likely to be highly demanded. 
     Accordingly, an object of the invention is to provide a motor cooling structure which can cool a motor with stabilized performance and higher efficiency than conventional ones, while having a simple structure, involving no fear of a cost hike, and nearly disallowing an increase in rotation resistance. 
     Solutions to the Problems 
     The present invention is intended to provide a cooling structure for cooling an electric motor, for a vehicle, including a stator fixed to a case member side and a rotor rotating relative to the stator, the cooling structure including an ejection hole of a coolant provided in a member, of the case member, which faces an end surface of the rotor in a rotary shaft direction, and coolant feeding means that feeds a coolant into a fluid path communicating with the ejection hole, in which the coolant ejected from the ejection hole is made to be sprayed onto least a coil end of the stator. 
     According to the configuration, the ejection hole for a coolant and the fluid path communicating with the ejection hole are provided in the member of the case member side of the electric motor, and the coolant fed by the coolant feeding means through the fluid path is ejected from the ejection hole, and sprayed onto the coil end of the stator. Since an ejection amount of the coolant is dependent on pressure of the coolant, the ejection amount of the coolant can be adjusted by adjusting the pressure when the coolant is fed by the coolant feeding means. Therefore, highly efficient and stable cooling can be achieved because a suitable amount of the coolant can be directly sprayed onto the coil end, even through the structure is simplified. 
     In addition, it is possible to suppress the coolant sprayed on the coil end from rebounding and invading the gap between the rotor by adjusting the ejection pressure of the coolant so as to fall within a suitable range. Since the sprayed coolant moves down due to the gravity and drops from the lower end of the coil end, the winding of the coil does not remain immersed in the coolant like in the former conventional examples (Patent Documents 1 and 2). For this reason, there is only a little risk of progress in degradation of the covering. From this point of view, it is preferable that a lowest portion of the stator is located at a higher position than a liquid surface even when a storage part of the coolant is provided in a lower portion of the case member of the electric motor, and it is more preferable that a partition plate is formed between the liquid surface and the lowest portion of the stator which is disposed above the storage part. 
     In regards to an appropriate position of the ejection hole, for example, a plurality of ejection holes may be provided so as to correspond to a plurality of coils of the stator, respectively so that the coolant is sprayed to each of the plurality of coils of the stator from the ejection holes, respectively. With this arrangement, cooling of the coil end is carried out more efficiently. In addition, when a rotary shaft of the rotor extends substantially horizontally, the number of the ejection holes of the coolant that are provided above the rotary shaft of the rotor may be larger than that provided below the rotary shaft of the rotor. With this arrangement, a large amount of oil can be sprayed to an upper portion of the coil end, and the whole can be more efficiently cooled. 
     In addition, when the stator is arranged to surround an outer circumference side of the rotor and fixed to the case member, if an outer circumference of the core of the stator is made to be in tight contact with the case member made of a metal, the outer circumference side of the coil can be effectively cooled via the case member. Accordingly, in this case, it is preferable that the ejection holes of the coolant be provided on an inner circumference side than the coil end of the stator so that cooling is started from the inner circumference side where heat easily accumulates. 
     Conversely, when the rotor is arranged to surround an outer circumference side of the stator, it is preferable that a portion which protrudes outward from an end surface of the rotor in the rotary shaft direction be provided near a lower end portion of the coil end of the stator. With this configuration, the coolant which drops from the lower end portion of the coil end hardly reaches the rotor, and it is advantageous in suppressing invasion of the coolant into the gap between the rotor and the stator. 
     At least a portion of the fluid path communicating with the election hole may be formed between a plurality of members of a case member side which mutually overlap each other, or the ejection holes may be formed in at least one of members of the case member side. For example, in a ease where the ejection hole is formed by cutting processing, an ejection direction of the ejection hole can be set up to exactly aim at the coil end. 
     The coolant which has used to cool the coil end of the stator may be circulated between a heat exchanger arranged outside the case member of the electric motor, and the heat exchanger may be disposed such that a traveling wind may pass by. With this configuration, the coolant, which has heat-exchanged with the traveling wind and become cold again, directly cools the coil end which is an exothermic portion of the electric motor, thereby acquiring as high cooling effect as possible. 
     Furthermore, an electric pump that is variable in operation speed may be further provided as coolant feeding means. With this configuration, an amount of the coolant is increased with an increase in the temperature of the electric motor, so that required sufficient cooling can be performed. The temperature of the electric motor may be measured by a sensor or may be estimated, for example, from a motor current value, etc. 
     On the one hand, when taking a cost into consideration, the coolant feeding means may be equipped with a mechanical pump which is mechanically connected to a traveling motor for a vehicle. With this configuration, since a discharge amount of the coolant increases with an increase in a rotation speed of the motor, as a result, cooling which is adaptively performed according to a temperature state of the electric motor can be carried out. 
     Furthermore, a gear type driving force transmission mechanism which transmits a torque of the electric motor may be accommodated in the case member of the electric motor to use the coolant for lubrication. When rotation of the electric motor is slowed down by the gear type driving force mechanism device and is then output, a torque load to the electric motor decreases, so that generation of heat can be suppressed. 
     In addition to the configuration, a fin may be further provided in the end surface of the rotor in the rotary shaft direction of the rotor so that air, which occurs due to the rotation, may be sent outward in the rotary shaft direction. With this configuration, the wind created by rotation of the fin will blow away the coolant which drops from the coil end so that the coolant may also move away from the rotor. Therefore, invasion of the coolant into the gap between the stator can be more certainly prevented. 
     Effects of the Invention 
     According to the cooling structure for cooling the electric motor for a vehicle according to the present invention, by including the means to feed the coolant, the coolant is made to be ejected from the ejection hole to the coil end of the stator at a suitable ejection pressure. Accordingly, although the cooling structure has a simplified structure, a suitable amount of the coolant can be directly sprayed onto the coil end which easily becomes a high temperature and hence the motor can be stably and efficiently cooled. Since a suitable amount of coolant is directly sprayed onto the coil end which easily becomes a high temperature, the motor can be stably and efficiently cooled. Since invasion of the coolant into the gap between the stator and the rotor can be suppressed, there is only a little fear that degradation of covering of the winding of the coil progresses. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a right side view illustrating main parts, such as a power plant, of an electronic motorcycle according to a first embodiment of the present invention. 
         FIG. 2  is a front view of the same electronic motorcycle viewed from the front. 
         FIG. 3  is a developed view illustrating the structure of a power plant of the same electronic motorcycle. 
         FIG. 4  is an explanatory view illustrating the structure of an ejection hole for cooling oil. 
         FIG. 5  is an explanatory view illustrating arrangement of main components in the power unit. 
         FIG. 6  is a view which is equivalent to  FIG. 1  and illustrates a second embodiment. 
         FIG. 7  is a view equivalent to  FIG. 3 . 
         FIG. 8  is a view equivalent to  FIG. 4 . 
         FIG. 9  is a view which is equivalent to  FIG. 1  and illustrates another embodiment in which an inverter and an oil tank are integrated with each other. 
         FIGS. 10(   a ) and  10 ( b ) are explanatory views schematically illustrating the structure of the oil cooler in which  FIG. 10(   a ) is a front view and  FIG. 10(   b ) is a cross-sectional view viewed from the right side. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. And throughout the following description, directions are used in reference to a vantage point of a driver of an electric motorcycle, seated on the driver&#39;s seat and facing forward. 
     First Embodiment 
       FIG. 1  is a right side view illustrating the main parts, such as a body frame, a power plant, and wheels, of an electric motorcycle  1  (electric vehicle) according to a first embodiment of the present invention, and  FIG. 2  is a front view illustrating the same viewed from the front. As illustrated in  FIG. 1 , the electric motorcycle  1  includes a front wheel  2  as a steering wheel and a rear wheel  3  as a driving wheel. The front wheel  2  is freely rotatably supported by lower ends of a pair of left and right front forks  4  which almost vertically extend. On the one hand, upper portions of the front forks  4  are supported by a steering shaft (not illustrated) via upper and lower brackets  4   a.    
     The steering shaft is freely rotatably supported in a state of being inserted in a head pipe  5  of the body, and constitutes a steering shaft. That is, a handle  6 , which horizontally extends like a bar, is attached to the upper bracket  4   a,  and the driver can achieve steering by swinging the front fork  4  and the front wheel  2  on the steering shaft by using the handle  6 . A right end of the handle  6  is gripped by the driver&#39;s right hand, and provided with an accelerator grip  7  which is rotatable by a twist of the driver&#39;s wrist. 
     The body frame of the electric motorcycle  1  includes, for example, a mainframe  8  which extends rearward and slightly inclines downward from the head pipe  5 . This is constituted by a pipe member with a polygonal section which is, for example, an extrusion-molded product of an aluminum alloy, and a front end part of the mainframe is welded to the head pipe  5 . Upper ends of a pair of left and right down frames  9  which extend downward are also welded to a position near the above-mentioned welding area, and these down frames  9  extend obliquely downward from the head pipe  5  while becoming horizontally farther from each other toward a lower side thereof until a horizontal distance between them reaches a predetermined value, and then further extend downward with a constant distance between them as illustrated in  FIG. 2 . 
     On the one hand, a portion of an upper frame part of a pivot frame  10  having, for example, a rectangular frame shape is welded to a rear end portion of the mainframe  8  such that the upper frame part horizontally extend in substantially perpendicular to a rear end portion of the mainframe  8 . A rear portion of a case member of a power plant  40  described below in detail is fastened to the pivot frame  10 , and a front portion of the case member is fastened to lower end portions of the down frames  9 . That is, a lower portion of the body frame is constituted by the case member of the power plant  40  in the present embodiment. 
     A front end portion of a swing arm  11  which supports the rear wheel  3  is supported in a vertically rockable manner between a left frame part and a right frame part of the pivot frame  10 , and the swing arm  11  extends rearward, slightly inclining downward, from a rocking pivot (pivot shaft). In the example illustrated in the drawing, a rear side portion of the swing arm  11  is bifurcated into two branches and the rear wheel  3  is supported between the two branches in a freely rotatable manner. On the one hand, a bulging portion which bulges downward is formed in a front portion of the swing arm  11 , thereby supporting a lower end portion of a damper  12 . An upper end portion of the damper  12  is supported on an extension  8   a  formed at the rear end portion of the mainframe  8 , and the damper  12  expands and contracts with vertical locking of the swing arm  11 . 
     As illustrated by an imaginary line in the drawing, a driver&#39;s seat  13  is disposed above the swing arm  11 , and a dummy tank  14  is disposed ahead of the driver&#39;s seat  13 . These are supported by a rear frame (not illustrated) which is connected to the mainframe  8 . In the case of an electric motorcycle, a fuel tank is unnecessary, but the dummy tank  14  is useful because a driver, seating in a horse-riding posture, would insert it between his/her knees, inside of the dummy tank  14  is used as an accommodation such as a helmet. In addition, similarly, as illustrated by an imaginary line, an under guard  15  made of resin is disposed under the power plant  40 . 
     In a space, between the front wheel  2  and the rear wheel  3 , in which an engine, a transmission, a throttle device, etc. are likely to be disposed if it is in the case of a conventional electric motorcycle, the power plant  40  equipped with a traveling motor  20  and/or a transmission device  30  (refer to  FIG. 3 ), a battery  50  for supplying power to the traveling motor  20 , and a power control controller  60  are disposed. 
     In the example illustrated in the drawing, the power plant  40  is connected from the lower end portion of the down frame  9  to the lower portion of the pivot frame  10 . Within a space above it, four batteries  50  are disposed in a relatively front position and the power control controller  60  is disposed in a relatively rear position. For example, the four batteries  50  are symmetrically mounted, two on the left side of the mainframe  8  and two on the right side of the mainframe  8 . As illustrated by a dashed line in  FIG. 2 , a vertically elongated space is formed between the left and right batteries  50 . Although not illustrated, a power supply line extends from the batteries  50  to the power plant  40  via the power control controller  60 . 
     Here, the traveling motor  20  is a motor/generator which performs a motor operation and a power generation operation, and drives the rear wheel  3  by performing the motor operation with the power supplied from the batteries  50  via the power control controller  60 . The traveling motor  20  operates as a generator during regenerative braking of the electric motorcycle  1 , so that the generated alternating current is converted into a direct current by an inverter of the power control controller  60  and the batteries  50  are charged. Control on the operation of the traveling motor  20  and/or charge-and-discharge control of the batteries  50  are mainly performed according to operation of the accelerator grip  7  and/or the traveling state of the electric motorcycle  1  as well known. 
       FIG. 3  illustrates the structure of the power plant  40  of the electric motorcycle  1 . The case member of the power plant  40  which is illustrated is an elliptical barrel with a closed bottom when viewed from the side, and includes an outer case member  41  which is arranged such that the bottom is disposed on the left side, and a cap  42  which is fastened in a manner of overlapping and closing the opening on the opposite side (the right side). As illustrated by an imaginary line in  FIG. 5 , an oil pan  43  which is tapered at the bottom and bulges downward is provided underneath the outer case member  41 . 
     Returning back to  FIG. 3 , the traveling motor  20  includes a stator  21  fixed to the outer case member  41 , and a rotor  22  which rotates relative to the stator  21 . In this example, the traveling motor  20  is formed by a so-called IPM motor in which a permanent magnet is embedded in an iron core of a rotor  22 . Although not illustrated in detail, the stator  21  has a typical structure in which a plurality of magnet coils  21   a  is wound around an iron core (stator core) formed of an electromagnetic steel plate. The stator  21  is arranged such as to surround an outer circumference side of the rotor  22 , and the outer circumference of the stator  21  is fixed to the outer case member  41 . 
     On the one hand, a steel motor shaft  23  passes through the rotor  22 , and both ends of the steel motor shaft  23  in a longitudinal direction are supported on the outer case member  41  via ball bearings  24 , respectively. A left side ball bearing  24  is fitted in a circular recess portion  41   a  in the bottom of the outer case member  41 , and a right side ball bearing  24  is disposed in a barrier wall part  44  of a different body fastened to the outer case member  41 . The motor shaft  23  passes through the barrier wall portion  44 , and protrudes from the right side of the barrier wall portion  44 . A leading end portion of the motor shaft  23  is provided with an output gear  25 . 
     As illustrated in even  FIG. 5 , a clutch shaft  31  as an input shaft of the transmission device  30  is disposed in the rear side of the traveling motor  20 , a rotation output from the traveling motor  20  is switched so as to be input or intercepted by a multiplate clutch  32  disposed at a right end thereof. Namely, a clutch gear  33  is externally freely rotatably fitted near the right end of the clutch shaft  31 , and meshes with an output gear  25  of the traveling motor  20 . When this clutch gear  33  is connected to the clutch shaft  31  by the multiplate clutch  32 , the clutch shaft  31  will come to rotate in conjunction with the motor shaft  23 . 
     An output shaft  34  of the transmission device  30  is disposed in parallel with the clutch shaft  31 , and is connected via a gear train  35  so as to be speed changeable. A speed change ratio of the input/output rotation, that is, a gear position of the transmission device  30  changes with a change in combination of the gears connected in the gear train  35 . In this way, a sprocket  36  is provided in a left end of the output shaft  34  which outputs the gear-shifted rotation and, although not illustrated, a chain is wound it and a sprocket of the rear wheel  3 . 
     —Structure for Cooling Traveling Motor, etc.— 
     In the present embodiment, in order to efficiently cool the traveling motor  20  and/or the inverter, non-conducting oil (coolant) is directly applied to a cooling fin provided in an inverter circuit board  60   a  and/or the magnet coil  21  a of the stator  21 . Namely, as illustrated in  FIG. 3 , in the traveling motor  20 , ejection holes  45   b  are provided in a bottom portion of the outer case member  41  facing an end surface on the left side of the rotor  22  and in the barrier wall portion  44  facing an end face on the right side of the rotor  22  such that the cooling oil can be ejected to be sprayed onto the coil end  21   b  of the stator  21 . 
     The ejection hole  45   b  illustrated on the left side in the drawing is described in detail. A relatively shallow large-diameter circular recess portion  41   b  continuous to the outer circumference of the recess portion  41   a,  into which a ball bearing  24  is fitted, is formed in the bottom portion of the outer case member  41 . A disk-like member  45  (member in the case member side) having a round hole at the center is fitted in the recess portion  41   b.  In the disk-like member  45  which is schematically illustrated in  FIG. 4 , a ring-shaped groove  45   a  is formed to open at a position around the outer circumference of a rear surface, thereby forming a ring-shaped oil path when fitted into the recess portion  41   b  of the outer case member  41  as described above. This ring-shaped oil path communicates with an oil path  41   c  (a portion of which is illustrated in  FIG. 3 ) which is formed in the outer case member  41 , thereby receiving the supplied cooling oil as described below. 
     And a plurality of holes  45   b  extending from the ring-shaped groove  45   a  to the front surface of the disc-like member  45  is provided at substantially regular intervals in a circumferential direction of the ring-shaped groove  45   a.  These holes  45   b  are formed by cutting, for example, like drilled holes. In the example of the drawing, each of 18 holes  45   b  is obliquely formed to become gradually nearer the outer circumference side from a position communicating the ring-shaped groove  45   a  toward the front surface of the disc-like member  45 . As indicated by an arrow in the drawing, the oil is radially obliquely ejected outward (hereinafter, the holes  45   b  are referred to as cooling oil ejection holes  45   b  or simply ejection holes  45   b ). 
     In this example, the ejection holes  45   b  are provided to correspond to the plurality of coils  21   a  wound around the core of the stator  21 , and the oil ejected from the ejection holes  45   b  is sprayed positions corresponding to the plurality of coils  21   a  of the stator  21 , respectively in the coil end  21   b  illustrated on the left side in  FIG. 1 . In the present embodiment, the disc-like member  45 , into which the ring-shaped groove  45   a,  to serve as an ring-shaped oil path, and the plurality of ejection holes  45   b  communicating with the ring-shaped groove  45   a  are processed, is also assembled in the barrier wall portion  44  illustrated on the right side in the drawing like the same way as described above. In regards to the right side coil end  21   b,  the oil which is ejected from the ejection hole  45   b  is sprayed on positions corresponding to the plurality of coils  21   a  of the stator  21 . 
     In this way, since the oil ejected from each of the plurality of ejection holes  45   b  is sprayed, the coil end  21   b  of the stator  21  which easily becomes a high temperature can be effectively cooled. Since the thermal conductivity of a coil in a winding direction is generally high, the cooling efficiency of the coil  21   a  disposed in a position corresponding to a cooling portion of the coil end  21   b  also improves. In addition, in regards to the holes  45   b  provided, the number of the holes in an upper portion of the disk-like member  45  may be larger than that in a lower portion of the disc-like member  45 . With this configuration, more oil can be sprayed on the upper portion of the coil end  21   b  so that the whole coil can be efficiently cooled. 
     In the present embodiment, the traveling motor  20  is fixed to the outer case member  41  in the outer circumference of the stator  21  as illustrated, and the outer circumference side of the stator  21  radiates heat to the air via the outer case member  41 . However, it can be said that the heat easily accumulates inside the inner circumference. Therefore, the oil ejection hole  45   b  is provided so as to face the end surface of the rotor  22  which is disposed on the inner circumference side, and is configured to spray the oil onto the inner circumference of the coil end  21   b  of the stator  21 , which is disposed on the outer circumference side. 
     In this way, by appropriately setting the orientation of the oil ejection holes  45   b  so as to aim at the coil end  21   b  on the outer circumference side, the oil can be sprayed onto the coil end  21   b  as intended, and there is a little risk that the ejected oil enters into the gap between the stator  21  and the rotor  22 . In addition, since the ejection pressure of the oil is adjusted to fall within in a suitable range by control of the oil pump  46  described below, the oil rebounding from the coil end  21   b  can be suppressed and there is a little risk that the oil, which rebounded, enters into the gap between the stator and the rotor. 
     In addition, in the example of the drawing, the fin  22   a  is provided in the end surface of the rotor  22  so that air may be sent outward in the rotary shaft direction (toward the right side if it is disposed on the right end surface, and toward the left side if it is disposed on the left end surface) along with the rotation. Since the wind which is created in this way will blow away the oil which drops from the coil end  21   b  from above so that the oil moves away from the rotor  22 , the invasion of the oil into the gap between the rotor  22  and the stator  21  is prevented. 
     As described above, the oil which was sprayed to the coil end  21   b  and deprived the coil end  21   b  of almost all of the heat flows downward along the windings extending in a circumferential direction of the coil end  21   b,  and drops downward from the lower end portion of the coil end  21   b,  reaching the oil pan  43 . Since the amount of oil stored in the oil pan  43  as illustrated in  FIG. 5  is set up such that the oil surface is lower than the lowest portion of the stator  21 , the windings of the coil  21   a  are not likely to remain immersed in the oil. Accordingly, this configuration is advantageous in suppressing the degradation f the covering. 
     Furthermore, in the present embodiment, since baffle plates  47  and  48  (partition plates between the oil surface of the oil and the lowest portion of the stator  21  disposed above the oil surface) are provided on the front side and the rear side of the oil pump  46 , respectively, there is also no risk of the stored oil rising along the wall surface of the oil pan  43  and reaching the traveling motor  20  at the time of the acceleration-and-deceleration of the electric motorcycle  1 . Yet furthermore, since the baffle plate  47  provided in front of the oil pump  46  is disposed to incline downward toward the rear side and the baffle plate  47  disposed behind the oil pump  46  is disposed to incline downward toward the front side, the oil which falls from above is smoothly guided into the oil pan  46 . 
     Then, the oil which comes to be stored in the oil pan  43  is pumped up by the electric oil pump  46  and fed to an oil cooler  70 . The oil pump  46  is driven by an electric motor, for example, thereby taking in the oil from a strainer  46   a  and discharging the oil from a discharge port  46   b.  In this example, the discharge port  46   b  extends through the outer case member  41 , and is equipped with an upstream end of a lower hose  71 . As illustrated in  FIG. 1 , the lower hose  71  passes through a lower portion of the power plant  40 , extends up to the front portion thereof, and is connected to a lower portion of the oil cooler  70  (heat exchanger) disposed in front of the batteries  50 . 
     The oil cooler  70  is disposed a little ahead of the down frame  9 , by and large, ranging from a position under the front end portion of the mainframe  8  to the lower end of the down frame  9 . When the electric motorcycle  1  is viewed from the front as illustrated in  FIG. 2 , the oil cooler  70  extends to be longer in the vertical direction and to be interposed between left and right front forks  4 , and a vertically long space S is provided between left and right batteries  50  disposed behind the oil cooler  70  as illustrated by a dashed line. Since the space S functions as a passage way for a traveling wind which passes by the oil cooler  70 , not only the traveling wind is smoothly introduced to the oil cooler  70  but also the traveling wind smoothly escapes through the vertically long space S. Accordingly, cooling efficiency may improve. Furthermore, the traveling wind also contributes to cooling of the batteries  50 . 
     In addition, the oil which is fed from the oil pump  46  to the lower portion of the oil cooler  70  as described above is cooled by heat-exchanging with the traveling wind while it is rising through the fluid path in the core of the oil cooler  70 . The oil which is cooled in this way is introduced into an upper hose  72  connected to the upper portion of the oil cooler  70 . In the example of the drawing, the upper hose  72  makes the space between the left and right batteries  50  extend rearward, and a downstream end of the upper hose  72  is connected to the power control controller  60 . 
     In the present embodiment, a case member of the power control controller  60  has a flat rectangular box shape, and is disposed to incline downward toward the rear side, on the rear side of the space disposed above the power plant  40 . The upper hose  72  is connected to the front side of the case member. As illustrated by a dashed line in the drawing, a circuit board  60   a  of an inverter is accommodated in the case member and the fluid path for the oil is formed such that the cooling fin joined to the circuit board may be immersed. The oil which flows through the fluid path effectively cools the circuit board  60   a.    
     A middle hose  73  for returning the oil to the power plant  40  is connected to the rear side of the case member of the power control controller  60 . The oil which is circulated in the inside of the middle hose  73  flows into the oil path  41   c  in the outer case member  41  from an oil inflow port provided in an upper portion of the outer case member  41  of the power plant  40 . Thus, the oil which is circulated in the inside of the oil path  41   c  is ejected from the ejection hole  45   b  as described above, and is sprayed onto the coil end  21   b  of the stator  21  of the traveling motor  20 . 
     That is, a circulation fluid path which circulates the oil among the power plant  40 , the power control controller  60 , and the oil cooler  70  is constituted by the lower hose  71 , the upper hose  72 , and the middle hose  73 . The oil cooled by the oil cooler  70  is first supplied to the power control controller  60  and is then supplied to the power plant  40  because an operation temperature of the traveling motor  20  is higher than an operation temperature of the inverter  60   a.    
     Although not illustrated in the drawing, the oil path  41   c  in the outer case member  41  is configured such that the oil may be supplied also to the ball bearing  24  which supports a motor shaft  23  of the traveling motor  20 , a bearing of the clutch shaft  31 , the output shaft  34 , etc. of the transmission device  30 , and/or the gear train  35 . The oil is supplied to lubricate and cool them. 
     Operation speed of the oil pump  46  which feeds and circulates the oil in the way described above can be changed by control of the electric motor which drives it. For example, the operation speed and a discharge amount of the oil increase according to a current value supplied to traveling motor  20  from an inverter, that is, with an increase in the current. When the control is performed like this, the ejection pressure of the oil ejected from the ejection hole  45   b  also becomes higher. However, the ejection pressure is excessively high, the amount of oil rebounding from the coil end  21   b  increases. Accordingly, the operation speed of the oil pump  46  is suppressed to be a predetermined value or below. 
     The operation control of the oil pump  46  may be performed by the power control controller  60 , for example. That is, the power control controller  60  functions also as control means of the oil pump  60  which monitors a supply current from the inverter  60   a  and controls the current value supplied to the electric motor of the oil pump  46  according to the supply current from the inverter  60   a.    
     As described above, in the electric motorcycle  1  according to the present embodiment as described above, the oil is directly sprayed especially to the coil end  216  of the stator  21  which easily becomes a high temperature in the traveling motor  20  of the power plant  40 , thereby effectively depriving the electric motor of the heat. Furthermore, the oil which has risen in temperature after being sprayed is circulated between the temperature-increased position and the oil cooler  70  so that the oil exchanges the heat with the traveling wind. With this configuration, even with a simple structure, a very high cooling effect of the motor is acquired. 
     In addition, a sufficient amount of oil can be supplied to the coil end  21   b  as intended and the rebounding of the oil from the coil end  21   b  can be suppressed by adjusting the ejection amount and the ejection pressure of the oil ejected from the oil ejection hole  45   b  by operation control of the oil pump  46 . Therefore, there is a little risk that the oil enters into the gap between the stator  21  and the rotor  22  and the rotation resistance rapidly increases. 
     In addition, before supplying the oil from the oil cooler  70  to the traveling motor  20 , the oil is introduced into the case member of the power control controller  70  so as to be brought into direct contact with the circuit board  60   a  of the inverter stored there, and the cooling of the inverter is very effectively performed. 
     Thus, since the oil which is circulated through the power plant  40 , the power control controller  60  and the oil cooler  70  deprives of the heat by direct contact with the stator  21  and/or the inverter  60   a  as described above, and other coolants such as LLC and the like need not to be used, troubles such as an increase in size or weight, a cost hike, and complicated maintenance hardly occur. 
     Second Embodiment 
       FIGS. 6 and 7  illustrate an electric motorcycle  101  according to a second embodiment of the present invention. Both figures are equivalent to  FIGS. 1 and 3  according to the first embodiment, respectively. Although an electric motorcycle  101  of the second embodiment mainly differs in the structure of a power plant from the first embodiment and hence differs also in the mounting positions of batteries  50  and a power control controller  60 , there are no other differences in the other basic structure. Accordingly, equivalent members are denoted by identical reference signs and a description thereof is omitted. 
     A power plant  80  of the second embodiment does not include a transmission device  30  so that the power plant  80  is very compact in a forward and rearward direction as illustrated in  FIG. 6 . For this reason, as illustrated in the drawing, down frames  9  extend rearward from a lower end, and a case member of the power plant  80  is fastened to a rear end. In addition, a pivot frame  10  is removed so that a rocking pivot (pivot shaft) of a swing arm  11  is provided in the case member of the power plant  80  and an upper end of the case member is fastened to a rear end portion of a mainframe  8 . 
     In addition, since there is a margin in a front space of the power plant  80 , in the example of the drawing, six batteries  50  can be mounted, three on the left side and three on the right side, and this margin is advantageous in increasing a traveling distance of the electric motorcycle  101 . On the one hand, since the power plant  80  is slightly longer in a vertical direction, the power control controller  60  is moved to above the mainframe  8 , and management of an upper hose  72  and a middle hose  73  is changed in conjunction with this. The upper hose  72  passes between the left and right batteries  50 , and then passes through the right side of the mainframe  8 , thereby extending up to the power control controller  60 . The middle hose  73  may be provided to also pass through the right side of the mainframe  8 . 
     As illustrated in  FIG. 7 , a traveling motor  90  of the power plant  80  is configured such that a permanent magnet  91  a is not embedded in but attached to a rotor  91 , and the traveling motor  90  is generally called an SPM motor. In the example of the drawing, two traveling motors, which have conventionally used as a generator of a motorcycle and the like, are used, sharing a motor shaft  93 . A driving gear  81  is installed at a center of the motor shaft  93 , and a driven gear  82  which meshes with the driving gear  81  is provided at an end portion of an output shaft  83  of the power plant  80 . 
     That is, in the example of the drawing, the power plant  80  does not include a transmission device  30  unlike the first embodiment, and rotation of the motor shaft  93  is slowed down according to a gear ratio of the driving gear  81  and the driven gear  82 , and is then transmitted to the output shaft  83 . 
     In addition, arrangement in the traveling motor  90  is in reverse to that of the first embodiment. That is, a stator  92  is located in an inner circumference side and a rotor  91  is arranged to surround an outer circumference of the stator  92 . For example, the traveling motor  90  illustrated on the right side in  FIG. 7  will be described. The rotor  91  is a flat bottomed cylindrical shape having an opening on the right side. The motor shaft  93  passes through a center of the bottom disposed on the left side. The motor shaft  93  and the bottom of the rotor  91  are spline-fitted. 
     A plurality of permanent magnets  91   a  having a thin plate shape is arranged in a circumference direction in an inner circumferential surface of a circumferential wall of the rotor  91 , and an iron core (core) of the stator  92  is arranged near the inner circumference side. A predetermined gap is formed between an outer circumferential surface of the stator and an inner circumferential surface of the permanent magnet  91   a  of the rotor  91 . 
     The stator  92  is attached, via a circular cylindrical support member  85 , to a case member  84  which constitutes a portion of the case member of the power plant  80 , and an ejection hole  86   b  for cooling oil is provided in the case member  84  which faces in proximity to the right end. That is, a circular ring-shaped member  86  is attached to the case member  84 , thereby forming a circular ring-shaped oil path  86   a.  The oil path  84   a  in the case member  84  communicates with this oil path  86   a,  so that the cooling oil is supplied. 
     As illustrated in an expanded manner in  FIG. 8 , the circular ring-shaped member  86  has a C-shaped section, and a circular ring-shaped groove in the inside thereof serves as the oil path  86   a.  And a plurality of holes (ejection holes  86   b ) is provided in the circular ring-shaped member  86  at almost regular intervals in a circumference direction such as to communicate with the ring-shaped oil path  86   a,  and each hole is formed in a manner of ejecting the cooling oil toward a coil end  92   b  of the stator  92 . 
     Although the details are not illustrated, the plurality of ejection holes  86   b  are provided so as to correspond to a plurality of magnet coils  92   a  wound around the core of the stator  92 , respectively like the first embodiment, and the oil ejected from each ejection hole  86   b  is sprayed to a position corresponding to the magnet coil  92   a  in the coil end  92   b  on the right side in the drawing. With this configuration, the coil end  92   b  of the stator  92  and furthermore the coils  92   a  can be effectively cooled. 
     In addition, the ejection holes  86   b  may also be provided such that the number of the ejection holes  86   b  disposed in an upper portion of the circular ring-shaped member  86  is larger than that in a lower portion of the circular ring-shaped member  86 . With this configuration, a larger amount of oil can be sprayed onto an upper portion of the coil end  92   b,  so that the whole can be efficiently cooled. 
     In this way, a portion of the oil which has deprived the coil end  92   b  of the heat flows downward from a support member  85  of the stator  92  via an inner surface of the case member  84 , and reaches an oil pan  87  located under the case member. In addition, a portion of the oil flows downward along windings of the coil end  92   b,  and drops downward from a lower end to the oil pan  87 . In this way, a portion of the oil which falls down is brought into contact with the rotor  91  but is sprayed by a centrifugal three of the rotor  91  which rotates at high speed. Therefore, there is a little risk of invasion of the oil into the gap between the rotor and the stator  92 . 
     Furthermore, in the example of the drawing, since a fin  91   b  is provided in an end portion of the rotor  91 , a wind traveling away from the rotor  91  is created due to the rotation. Accordingly, the oil is sprayed away by the wind. In the example of the drawing, an oil surface of the oil stored in the oil pan  87  is set to a position lower than a lowest portion of the driven gear  82  so that agitating resistance may not be generated. 
     In addition, although not illustrated, the rotor  91  is reduced in size in a rotary shaft direction, and a right end is moved to the left side. However, a portion which protrudes outward from a right end surface of the rotor  91  may be provided near a lower end portion of coil end  92   b  of the stator  92 . With this configuration, the oil which falls from the lower end portion of the coil end  92   b  hardly reaches the rotor  91 . Accordingly, this configuration is advantageous in preventing invasion of the oil into the gap between the rotator and the stator  92 . 
     Other Embodiment 
     The embodiments in the above description are just only examples, and do not limit the present invention, its applications, and its use. For example, in the first embodiment, ejection holes  45   b  for cooling oil are provided on left and right sides of a rotor  22  of a traveling motor  20 , respectively, and oil is sprayed onto coil ends  21   a  on both left and right sides of a stator  21 . However, the present invention is not limited to this. For example, the oil may be sprayed onto only either one coil end like in the second embodiment. 
     Although the oil pump  46  for feeding cooling oil is accommodated in the case member of the power plant  40  or  80  to pump out the oil stored in the oil pan  46  or  87  in the above-described embodiments, the present invention is not limited thereto. That is, the oil pump  46  may be disposed near an oil cooler  70 . 
     Conversely, when it is accommodated in the case member of the power plant  40  or  80 , a mechanical pump may be connected so as to be driven by a motor shaft  23  or  92  of a traveling motor  20  or  90 . When configured in this way, since a discharge amount of the oil from the pump increases as rotation speed of the traveling motor  20  or  90  increases, as a result, cooling adaptively performed according to a temperature state of the traveling motor  20  or  90  can be achieved. 
     Although cooling oil is sent out from the inside of the case member of the power plant  40  or  80  and is circulated between the case member and the oil cooler  70  through which the traveling wind passes in the above-described embodiments, the present invention is not limited thereto. The oil may be circulated within the case member and the case member may be cooled by air or another cooling water. 
     Although both of the traveling motor  20  or  90  and the power control controller  60  are cooled by oil in the above-described embodiments, only either one may be cooled. For example, in regards to the power control controller  60 , the cooling fin joined to the circuit board  60   a  of the inverter is not immersed in the oil but the circuit board  60   a  may be cooled via a cooler in which oil flows. 
     The circuit board  60   a  of the inverter may be integrally formed with the oil cooler. For example, as illustrated in  FIGS. 9 and 10 , the oil cooler  75  has a recess portion  75   b  which is open at a rear side so that an upper tank  75   a  thereof may be formed in a large size as compared with the first embodiment, and have a flat U shape when viewed from above. And the circuit board  60   a  of the inverter may be installed to be fitted into the recess portion  75   b.  The cooling fin  60   b  is joined to a front surface of the circuit board  60   a  like the first embodiment, and this passes through a wall surface of the recess portion  75   b  of the upper tank  75   a  and is immersed in the oil in the tank. 
     According to this configuration, the oil which is fed from the oil pump  46  of the power plant  40  and introduced into the lower tank  75   c  of the oil cooler  75  is cooled by heat exchange with the traveling wind while it is rising through the fluid path in the core  75   d  of the oil cooler  75 . Thus, the oil effectively cools the circuit board  60   a  of the inverter in the upper tank  75   a  of the oil cooler  75 , and then flows into the upper hose  72  connected to the upper tank  75   a.    
     Although a description is made about the electric motorcycle  1  in each of the above embodiments, the electric vehicle according to the present invention is not limited to the motorcycle, and for example, it may be an ATV (All Terrain Vehicle), a mechanical mule, and the like. 
     INDUSTRIAL APPLICABILITY 
     As described above, since the cooling structure for cooling an electric vehicle according to the present invention can obtain an increased cooling efficiency compared with a conventional art, and has a simple structure which hardly increases size and weight and/or causes a cost hike, it is especially useful for an electric motorcycle. 
     DESCRIPTION OF REFERENCE SIGNS 
       1 : Electric motorcycle (vehicle) 
       2 : Front wheel 
       20 ,  90 : Traveling motor (electric motor for traveling) 
       21 ,  92 : Stator 
       21   a,    92   a:  Magnetic coil 
       21   b,    92   b:  Coil end 
       22 ,  91 : Rotor 
       22   a,    91   b:  Fin 
       30 ,  81 ,  82 : Transmission device (gear type driving force transmission mechanism) 
       40 ,  80 : Power plant 
       41 : Outer case member (case member of an electric motor) 
       41   c,    84   a:  Fluid path communicating with ejection hole 
       45 : Disk-like member (member of case member side) 
       45   b,    86   b:  Ejection hole for cooling oil 
       46 : Electric pump (cooling liquid feeding means) 
       60 : Power control controller (control means) 
       70 : Oil cooler (heat exchanger) 
       71 : Lower hose (circulation fluid path) 
       72 : Upper hose (circulation fluid path) 
       73 : Middle hose (circulation fluid path)