Patent Publication Number: US-2021167666-A1

Title: Cooling device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2019-219005 filed on Dec. 3, 2019, the entire contents of which are herein incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a cooling device mounted on a vehicle. 
     Background Art 
     Japanese Laid-Open Patent Publication No. JP-2010-064651 discloses a temperature control device for a motor driving system of a vehicle. The motor driving system includes a motor, an inverter for controlling the motor, and a battery for supplying power to the inverter. The temperature control device is provided with a pipe through which cooling water flows. The pipe is arranged to cool the motor, the inverter, and the battery in parallel. When the battery temperature is high, much cooling water is supplied to the battery. On the other hand, when the motor temperature is high, much cooling water is supplied to the motor and the inverter. A distribution ratio of the cooling water distributed to the motor side and the cooling water distributed to the inverter side is constant. 
     Japanese Laid-Open Patent Publication No. JP-2018-026974 discloses a cooling device for cooling a motor. The cooling device includes a first flow path for cooling a stator coil, a second flow path for cooling a permanent magnet of a rotor, a distributor for distributing coolant to the first flow path and the second flow path, and a distribution control unit. When a maximum system voltage is supplied to an inverter, an amount of coolant distributed to the first flow path is a first distribution amount, and an amount of coolant distributed to the second flow path is a second distribution amount. When the motor is subjected to field-weakening control, the distribution control unit sets the amount of coolant distributed to the first flow path to be smaller than the first distribution amount, and sets the amount of coolant distributed to the second flow path to be larger than the second distribution amount. 
     SUMMARY 
     Cooling a motor mounted on a vehicle and an inverter driving the motor is considered. According to the technique disclosed in Japanese Laid-Open Patent Publication No. JP-2010-064651, the motor and the inverter are cooled in parallel. The distribution ratio of the cooling water distributed to the motor side and the cooling water distributed to the inverter side is constant. 
     However, a rotor and a stator of the motor and the inverter may have different heat generation characteristics. It is inefficient to distribute the cooling water to components having different heat generation characteristics at a constant distribution ratio. 
     For example, consider a situation where a first component and a second component have different heat generation characteristics, the first component is at a relatively high temperature, and the second component is at a relatively low temperature. In order to effectively cool the high-temperature first component, it is necessary to distribute much cooling water to the first component. When the distribution ratio is constant, it is necessary to increase a total flow rate of the cooling water in order to increase the cooling water distributed to the first component. As the total flow rate of the cooling water is increased, the cooling water distributed to the second component also is increased. That is, when the cooling water distributed to the first component is increased, the cooling water distributed to the second component also is increased in conjunction with that. However, a large amount of cooling water is not required to cool the relatively low-temperature second component. It is inefficient to distribute excess cooling water to the second component. 
     An object of the present disclosure is to provide a technique that can efficiently cool a motor mounted on a vehicle and an inverter driving the motor. 
     With regard to cooling a motor and an inverter, the inventor of the present disclosure has focused on the following point. There is a difference or similarity in state between a rotor and a stator of the motor and the inverter. For example, the rotor differs from the stator and the inverter in that it performs a rotational motion. On the other hand, the inverter and the stator (stator coil) have in common that a current is supplied thereto from a power source. Such the difference or similarity is considered to lead to a difference or similarity in heat generation characteristics. That is, it is considered that the heat generation characteristics of the inverter and the stator are relatively similar to each other and the heat generation characteristics of the rotor are different from the heat generation characteristics of the inverter and the stator. Therefore, according to the present disclosure, “the inverter-stator pair” and “the rotor” are cooled independently and separately. 
     A first aspect is directed to a cooling device that cools a motor mounted on a vehicle and an inverter driving the motor. 
     The cooling device includes: 
     a common flow path through which coolant flows; 
     a first flow path branching from the common flow path and arranged to cool the inverter and a stator of the motor; 
     a second flow path branching from the common flow path, being independent of the first flow path, and arranged to cool a rotor of the motor; and 
     a distribution structure configured to distribute the coolant to the first flow path and the second flow path, and to change a distribution ratio of a first coolant distributed to the first flow path out of the coolant and a second coolant distributed to the second flow path out of the coolant. 
     A second aspect further has the following feature in addition to the first aspect. 
     The first flow path is arranged to cool the inverter and the stator in series. 
     A third aspect further has the following feature in addition to the second aspect. 
     The first flow path is arranged such that the inverter is located upstream of the stator in the first flow path. 
     A fourth aspect further has the following feature in addition to any one of the first to third aspects. 
     The distribution structure changes the distribution ratio according to a rotational speed of the rotor. 
     A fifth aspect further has the following feature in addition to the fourth aspect. 
     A flow rate of the first coolant when the rotational speed is lower than a first rotational speed is greater than a flow rate of the first coolant when the rotational speed is equal to or higher than the first rotational speed. 
     A flow rate of the second coolant when the rotational speed is equal to or higher than a second rotational speed is greater than a flow rate of the second coolant when the rotational speed is lower than the second rotational speed. 
     A sixth aspect further has the following feature in addition to the fifth aspect. 
     When the rotational speed is lower than a third rotational speed, the flow rate of the first coolant is greater than the flow rate of the second coolant. 
     When the rotational speed is higher than the third rotational speed, the flow rate of the second coolant is greater than the flow rate of the first coolant. 
     A seventh aspect further has the following feature in addition to any one of the first to sixth aspects. 
     The rotor includes a rotor shaft and a rotor core around the rotor shaft. 
     The second flow path includes: 
     a connection flow path connecting a branch point of the common flow path and the second flow path and the rotor shaft; 
     a rotor shaft flow path connected to the connection flow path and arranged inside the rotor shaft; and 
     a rotor core flow path connecting the rotor shaft flow path and an outside of the rotor core through an inside of the rotor core. 
     The distribution structure includes the branch point, the second flow path, and the rotor. 
     An eighth aspect is directed to a cooling device that cools a motor mounted on a vehicle and an inverter driving the motor. 
     The cooling device includes: 
     a common flow path through which coolant flows; 
     a first flow path branching from the common flow path and arranged to cool the inverter and a stator of the motor; and 
     a second flow path branching from the common flow path, being independent of the first flow path, and arranged to cool a rotor of the motor. 
     The rotor includes a rotor shaft and a rotor core around the rotor shaft. 
     The second flow path includes: 
     a connection flow path connecting a branch point of the common flow path and the second flow path and the rotor shaft; 
     a rotor shaft flow path connected to the connection flow path and arranged inside the rotor shaft; and 
     a rotor core flow path connecting the rotor shaft flow path and an outside of the rotor core through an inside of the rotor core. 
     According to the first aspect, the inverter-stator pair is cooled by the first coolant distributed to the first flow path. The inverter and the stator having similar heat generation characteristics can be collectively cooled by the first coolant, which is less wasteful and more efficient. The rotor having different heat generation characteristics is cooled by the second coolant distributed to the second flow path being independent of the first flow path. Furthermore, the distribution ratio of the first coolant and the second coolant is variable. Therefore, when it is desired to increase one of the first coolant and the second coolant, the other of the first coolant and the second coolant is prevented from unnecessarily increasing in conjunction with that. That is, it is possible to suppress a wasteful distribution of the coolant and to efficiently distribute the coolant to the first coolant and the second coolant. It is thus possible to efficiently cool the inverter, the stator, and the rotor. 
     According to the second aspect, the first flow path is arranged so as to cool the inverter and the stator in series. Since each of the inverter and the stator can be cooled by using the entire first coolant, a cooling efficiency is improved. In addition, since there is no need to further branch the first flow path or further divide the first coolant, a structure related to the first flow path is simplified. 
     According to the third aspect, the inverter is located upstream of the stator in the first flow path. It is thus possible to more effectively cool the inverter whose maximum allowable temperature is relatively low. 
     According to the fourth aspect, the distribution ratio is changed according to the rotational speed of the rotor. When the rotational speed is low, heat generations in the inverter and the stator become large. On the other hand, when the rotational speed is high, a heat generation in the rotor becomes large. Changing the distribution ratio according to the rotational speed makes it possible to further efficiently cool the inverter, the stator, and the rotor. 
     According to the fifth aspect, it is possible to effectively cool the high-temperature inverter and stator in a low-speed region and to save the first coolant in a high-speed region. That is, it is possible to efficiently cool the inverter and the stator. Moreover, it is possible to effectively cool the high-temperature rotor in the high-speed region and to save the second coolant in the low-speed region. That is, it is possible to efficiently cool the rotor. 
     According to the sixth aspect, a magnitude relationship between the flow rate of the first coolant and the flow rate of the second coolant is reversed between the low-speed region and the high-speed region. It is thus possible to cool the inverter-stator pair and the rotor in a well-balanced manner. 
     According to the seventh and eighth aspects, the change in the distribution ratio depending on the rotational speed of the rotor is automatically achieved due to the structure of the second flow path arranged inside the rotor. Since control using a controller or the like is unnecessary, a structure of the cooling device is simplified and a manufacturing cost is reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram showing a configuration example of a vehicle according to a first embodiment of the present disclosure; 
         FIG. 2  is a schematic diagram showing a configuration example of a cooling device according to the first embodiment of the present disclosure; 
         FIG. 3  is a schematic diagram showing a configuration example of an inverter and a first flow path according to the first embodiment of the present disclosure; 
         FIG. 4  is a schematic diagram showing a configuration example of a motor, a first flow path, and a second flow path according to the first embodiment of the present disclosure; 
         FIG. 5  is a schematic diagram showing a configuration example of a distribution structure according to the first embodiment of the present disclosure; 
         FIG. 6  is a conceptual diagram showing an example of a relationship between a coolant flow rate and a rotational speed in the cooling device according to a second embodiment of the present disclosure; 
         FIG. 7  is a conceptual diagram showing another example of a relationship between a coolant flow rate and a rotational speed in the cooling device according to the second embodiment of the present disclosure; 
         FIG. 8  is a schematic diagram showing a configuration example of the distribution structure according to the second embodiment of the present disclosure; 
         FIG. 9  is a schematic diagram showing a configuration example of the distribution structure according to a third embodiment of the present disclosure; 
         FIG. 10  is a schematic diagram showing a configuration example of the motor, the first flow path, and the second flow path according to a fourth embodiment of the present disclosure; and 
         FIG. 11  is a schematic diagram showing a configuration example of the cooling device according to a fifth embodiment of the present disclosure. 
     
    
    
     EMBODIMENTS 
     Embodiments of the present disclosure will be described with reference to the attached drawings. 
     1. First Embodiment 
     1-1. Vehicle 
       FIG. 1  is a schematic diagram showing a configuration example of a vehicle  1  according to the present embodiment. The vehicle  1  is, for example, an electric vehicle or a hybrid vehicle. An inverter  100  and a motor  200  are mounted on the vehicle  1 . 
     The inverter  100  drives the motor  200 . More specifically, the inverter  100  is connected to a power source (not shown), and power is supplied from the power source to the inverter  100 . The inverter  100  drives the motor  200  by supplying a motor drive current to the motor  200 . 
     The motor  200  operates (rotates) by being driven by the inverter  100 . Examples of the motor  200  include a synchronous motor, an induction motor, a brushless DC motor, and the like. The motor  200  includes a stator  210  and a rotor  220 . The motor drive current supplied from the inverter  100  flows through the stator  210  (i.e., a stator coil), and thereby the rotor  220  rotates. 
     The motor  200  generates a force by rotating. Typically, the motor  200  generates a driving force for the vehicle  1 . In this case, the motor  200  generates a torque that rotates wheels  2  of the vehicle  1 . 
     The vehicle  1  is further provided with a cooling device  10  that cools the inverter  100  and the motor  200  (the stator  210  and the rotor  220 ). Hereinafter, the cooling device  10  according to the present embodiment will be described in more detail. 
     1-2. Cooling Device 
       FIG. 2  is a schematic diagram showing a configuration example of the cooling device  10  according to the present embodiment. The cooling device  10  includes a flow path FP through which coolant CL flows, and a pump  20  that feeds the coolant CL into the flow path FP. The coolant CL may be oil or may be water. The flow path FP is arranged so as to cool the inverter  100  and the motor  200  (i.e., the stator  210  and the rotor  220 ). 
     With regard to the arrangement of the flow path FP for cooling the inverter  100  and the motor  200 , the inventor of the present disclosure has focused on the following point. There is a difference or similarity in state between the inverter  100 , the stator  210 , and the rotor  220 . For example, the rotor  220  differs from the stator  210  and the inverter  100  in that it performs a rotational motion. On the other hand, the inverter  100  and the stator  210  (stator coil) have in common that a current is supplied thereto from a power source. Such the difference or similarity is considered to lead to a difference or similarity in heat generation characteristics. That is, it is considered that the heat generation characteristics of the inverter  100  and the stator  210  are relatively similar to each other and the heat generation characteristics of the rotor  220  are different from the heat generation characteristics of the inverter  100  and the stator  210 . 
     Therefore, according to the present embodiment, independent and separate flow paths are provided for “the inverter  100 -stator  210  pair” and “the rotor  220 ”, respectively. A “first flow path FP 1 ” is for cooling the inverter  100 -stator  210  pair. A “second flow path FP 2 ” is for cooling the rotor  220 . The first flow path FP 1  and the second flow path FP 2  are independent of each other. 
     More specifically, as shown in  FIG. 2 , the flow path FP includes a common flow path FPC, the first flow path FP 1 , the second flow path FP 2 , and a return flow path FPR. 
     The coolant CL is fed from the pump  20  to the common flow path FPC. In other words, the coolant CL outputted from the pump  20  first flows through the common flow path FPC. The common flow path FPC branches into the first flow path FP 1  and the second flow path FP 2  at a branch point BR. 
     The coolant CL flowing through the common flow path FPC is distributed to the first flow path FP 1  and the second flow path FP 2 . A first coolant CL 1  is a portion that is distributed to the first flow path FP 1  out of the coolant CL. A second coolant CL 2  is a portion that is distributed to the second flow path FP 2  out of the coolant CL. A structure that distributes the coolant CL flowing through the common flow path FPC to the first flow path FP 1  and the second flow path FP 2  is hereinafter referred to as a “distribution structure  30 .” There are various examples of the distribution structure  30 . Some examples of the distribution structure  30  will be described later. 
     The first flow path FP 1  branches from the common flow path FPC at the branch point BR. The first flow path FP 1  is arranged so as to cool the inverter  100  and the stator  210 . That is, the inverter  100 -stator  210  pair is cooled by the first coolant CL 1  distributed to the first flow path FP 1 . The inverter  100  and the stator  210  having similar heat generation characteristics can be collectively cooled by the first coolant CL 1 , which is less wasteful and more efficient. 
     In some embodiments, the inverter  100  and the stator  210  may be arranged in series along the first flow path FP 1 . In other words, the first flow path FP 1  may be arranged so as to cool the inverter  100  and the stator  210  in series (in order). In this case, each of the inverter  100  and the stator  210  can be cooled by using the entire first coolant CL 1 , and thus a cooling efficiency is improved. In addition, since there is no need to further branch the first flow path FP 1  or further divide the first coolant CL 1 , a structure related to the first flow path FP 1  is simplified. 
     In some embodiments, the inverter  100  may be located upstream of the stator  210  in the first flow path FP 1 . A maximum allowable temperature of the inverter  100  including power elements is lower than that of the stator  210 . Since the inverter  100  is located upstream of the stator  210 , it is possible to more effectively cool the inverter  100 . 
     In the example shown in  FIG. 2 , the stator  210  and the rotor  220  of the motor  200  are placed inside a motor case  201 . The inverter  100  is placed outside the motor case  201 . The first flow path FP 1  extends from the branch point BR to the inside of the motor case  201  via the inverter  100 . The first coolant CL 1  distributed to the first flow path FP 1  first cools the inverter  100  and then cools the stator  210  placed inside the motor case  201 . 
     The second flow path FP 2  branches from the common flow path FPC at the branch point BR. The second flow path FP 2  is independent of the first flow path FP 1  and is arranged so as to cool the rotor  220 . That is, the rotor  220  is cooled by the second coolant CL 2  distributed to the second flow path FP 2 . 
     The first coolant CL 1  after cooling the stator  210  and the second coolant CL 2  after cooling the rotor  220  gather at a bottom of the motor case  201 . A outlet  205  for discharging the coolant CL is provided at the bottom of the motor case  201 . The return flow path FPR connects the outlet  205  and the pump  20 . The coolant CL discharged from the outlet  205  returns to the pump  20  through the return flow path FPR. 
     The cooling device  10  may include a radiator  40  for cooling the coolant CL. The radiator  40  is provided in the common flow path FPC or the return flow path FPR. 
     1-3. Variable Distribution Ratio 
     According to the present embodiment, a “distribution ratio R” of the first coolant CL 1  distributed to the first flow path FP 1  and the second coolant CL 2  distributed to the second flow path FP 2  is variable. That is, the distribution structure  30  is capable of changing the distribution ratio R of the first coolant CL 1  and the second coolant CL 2 . 
     As a comparative example, a case where the distribution ratio R is constant is considered. As described above, the heat generation characteristics of the inverter  100  and the stator  210  are relatively similar to each other, and the heat generation characteristics of the rotor  220  are different from the heat generation characteristics of the inverter  100  and the stator  210 . Consider a situation where the inverter  100  and the stator  210  are at relatively low temperatures while the rotor  220  is at a relatively high temperature due to the difference in heat generation characteristics. In order to effectively cool the high-temperature rotor  220 , it is necessary to increase the second coolant CL 2 . When the distribution ratio R is constant, it is necessary to increase a total flow rate of the coolant CL in order to increase the second coolant CL 2 . As the total flow rate of the coolant CL is increased, the first coolant CL 1  also is increased. That is, when the second coolant CL 2  is increased, the first coolant CL 1  also is increased in conjunction with that. However, a large amount of the first coolant CL 1  is not required to cool the inverter  100  and the stator  210  of a relatively low temperature. It is inefficient to distribute excess first coolant CL 1  to the inverter  100  and the stator  210 . 
     Moreover, in order to increase the total flow rate of the coolant CL, the cooling device  10  is required to have a large structure. For example, a large pipe, a large pump  20 , a large radiator  40 , and the like are required. Such an increase in size of the cooling device  10  causes an increase in weight and cost. Further, in order to increase the total flow rate of the coolant CL, it is necessary to increase a workload of the pump  20 . This leads to a deterioration in fuel efficiency (electricity cost). 
     On the other hand, according to the present embodiment, the distribution ratio R of the first coolant CL 1  for cooling the inverter  100 -stator  210  pair and the second coolant CL 2  for cooling the rotor  220  is variable. Therefore, when it is desired to increase one of the first coolant CL 1  and the second coolant CL 2 , the other of the first coolant CL 1  and the second coolant CL 2  is prevented from unnecessarily increasing in conjunction with that. That is, it is possible to suppress a wasteful distribution of the coolant CL and to efficiently distribute the coolant CL to the first coolant CL 1  and the second coolant CL 2 . It is thus possible to efficiently cool the inverter  100 , the stator  210 , and the rotor  220 . 
     Moreover, according to the present embodiment, an unnecessary increase in the total flow rate of the coolant CL is suppressed. Therefore, miniaturization of the cooling device  10  is possible. The miniaturization of the cooling device  10  provides a reduction in weight and cost. In addition, the increase in workload of the pump  20  for supplying the coolant CL is suppressed which provides an improvement of fuel efficiency. 
     1-4. Configuration Example 
     1-4-1. Configuration Example of Inverter and First Flow Path 
       FIG. 3  is a schematic diagram showing a configuration example of the inverter  100  and the first flow path FP 1  according to the present embodiment. The inverter  100  includes a case  110  and an inverter module  120  installed in the case  110 . The case  110  is made of, for example, metal. The inverter module  120  includes elements necessary for the function of the inverter  100 , such as power elements. 
     The first flow path FP 1  is arranged to be in contact with the case  110 . More specifically, the first flow path FP 1  includes a contact flow path FP 1 C, an upstream flow path FP 11 , and a downstream flow path FP 12 . The contact flow path FP 1 C is in contact with the case  110  of the inverter  100 . The upstream flow path FP 11  connects the branch point BR and the contact flow path FP 1 C. The downstream flow path FP 12  is connected downstream of the contact flow path FP 1 C. 
     The first coolant CL 1  flows through the upstream flow path FP 11 , the contact flow path FP 1 C, and the downstream flow path FP 12  in this order. The inverter module  120  is cooled by the first coolant CL 1  flowing through the contact flow path FP 1 C. 
     1-4-2. Configuration Example of Motor, First Flow Path, and Second Flow Path 
       FIG. 4  is a schematic diagram showing a configuration example of the motor  200 , the first flow path FP 1 , and the second flow path FP 2  according to the present embodiment. The stator  210  and the rotor  220  of the motor  200  are placed inside the motor case  201 . The outlet  205  for discharging the coolant CL is provided at the bottom of the motor case  201 . 
     The stator  210  includes a stator coil  211  and a stator core  212 . The motor drive current is supplied to the stator coil  211  from the inverter  100 . 
     The downstream flow path FP 12  of the first flow path FP 1  is arranged so as to cool at least the stator coil  211 . More specifically, the downstream flow path FP 12  is arranged in the vicinity of the stator  210 . The downstream flow path FP 12  has openings at positions facing the stator coil  211 . At least a part of the first coolant CL 1  flowing through the downstream flow path FP 12  is discharged from the openings toward the stator coil  211 , thereby cooling the stator coil  211 . 
     Further, another opening may be provided at a position facing the stator core  212 . A part of the first coolant CL 1  is discharged from the opening toward the stator core  212 , thereby cooling the stator core  212 . Since the stator core  212  is cooled, the stator coil  211  is indirectly cooled. 
     The rotor  220  is surrounded by the stator  210 . The rotor  220  includes a rotor shaft  221  (rotating shaft), a rotor core  222  around the rotor shaft  221 , and a permanent magnet  223  embedded in the rotor core  222 . The rotor shaft  221  is rotatably supported by the motor case  201 . In the following description, a Z-direction is an axial direction parallel to the rotor shaft  221 , and an R-direction is a radial direction orthogonal to the Z-direction. 
     The second flow path FP 2  includes a connection flow path FP 20 , a rotor shaft flow path FP 21 , and a rotor core flow path FP 22 . The connection flow path FP 20  connects the branch point BR of the common flow path FPC and the second flow path FP 2  and the rotor shaft  221 . The rotor shaft flow path FP 21  is arranged (formed) inside the rotor shaft  221  and is parallel to the Z-direction. An upstream end of the rotor shaft flow path FP 21  is connected to the connection flow path FP 20 , and a downstream end thereof is connected to the rotor core flow path FP 22 . 
     The rotor core flow path FP 22  is arranged (formed) inside the rotor core  222 . More specifically, the rotor core flow path FP 22  connects the downstream end of the rotor shaft flow path FP 21  and an outside of the rotor core  222  through the inside of the rotor core  222 . In the example shown in  FIG. 4 , a rotor core flow path FP 22 - 1  extends in the R-direction from the downstream end of the rotor shaft flow path FP 21  toward the inside of the rotor core  222 . Further, a rotor core flow path FP 22 - 2  extends in the Z-direction from a downstream end of the rotor core flow path FP 22 - 1  toward the outside of the rotor core  222 . The rotor core flow path FP 22 - 2  is arranged in the vicinity of the permanent magnet  223  embedded in the rotor core  222 . 
     The second coolant CL 2  flows through the connection flow path FP 20 , the rotor shaft flow path FP 21 , and the rotor core flow path FP 22  in this order, and is eventually discharged to the motor case  201 . The rotor  220  is cooled by the second coolant CL 2  flowing through the rotor shaft flow path FP 21  and the rotor core flow path FP 22 . 
     1-4-3. Example of Distribution Structure 
       FIG. 5  is a schematic diagram showing a configuration example of the distribution structure  30  according to the present embodiment. The distribution structure  30  includes a distributor  31  and a controller  32 . 
     The distributor  31  is interposed between the common flow path FPC, the first flow path FP 1 , and the second flow path FP 2 . The distributor  31  distributes the coolant CL flowing through the common flow path FPC to the first flow path FP 1  and the second flow path FP 2 . Furthermore, the distributor  31  includes a solenoid valve  33 . An opening area for the first flow path FP 1  and an opening area for the second flow path FP 2  are changed by an operation of the solenoid valve  33 . In other words, the distribution ratio R of the first coolant CL 1  distributed to the first flow path FP 1  and the second coolant CL 2  distributed to the second flow path FP 2  is changed by the operation of the solenoid valve  33 . 
     The controller  32  controls the operation of the solenoid valve  33  of the distributor  31 . That is, the controller  32  changes the distribution ratio R of the first coolant CL 1  and the second coolant CL 2 . For example, the controller  32  calculates or acquires a target distribution ratio and controls the operation of the solenoid valve  33  of the distributor  31  such that the target distribution ratio is achieved. 
     2. Second Embodiment 
     In a second embodiment, “copper loss” and “iron loss” which are causes of heat generation are considered. The iron loss includes hysteresis loss and eddy current loss. 
     The inverter  100  includes the power elements and a large current flows therein. The motor drive current is supplied to the stator  210  (the stator coil  211 ). As to the heat generations in such the inverter  100  and the stator  210 , the copper loss is dominant. The copper loss increases in proportion to the square of current. Therefore, the heat generations in the inverter  100  and the stator  210  become particularly large in a “low-speed and large-torque region” where the motor drive current is large. 
     On the other hand, as to the heat generation in the rotor  220  including a magnetic material and performing the rotational motion, the iron loss is dominant. The iron loss increases as a rotational speed N of the rotor  220  increases. Therefore, the heat generation in the rotor  220  becomes particularly large in a “high-speed region.” 
     As described above, the heat generation characteristics of the inverter  100 , the stator  210 , and the rotor  220  depend on the rotational speed N of the rotor  220 . When the rotational speed N is low, the heat generations in the inverter  100  and the stator  210  become large. On the other hand, when the rotational speed N is high, the heat generation in the rotor  220  becomes large. In the second embodiment, the distribution ratio R is changed according to the rotational speed N in consideration of such the difference in the heat generation characteristics depending on the rotational speed N. 
       FIG. 6  shows an example of a relationship between a coolant flow rate and the rotational speed N. A horizontal axis represents the rotational speed N of the rotor  220 . A vertical axis represents a first coolant flow rate QF 1  and a second coolant flow rate QF 2 . The first coolant flow rate QF 1  is a flow rate of the first coolant CL 1  distributed to the first flow path FP 1 . The second coolant flow rate QF 2  is a flow rate of the second coolant CL 2  distributed to the second flow path FP 2 . The distribution ratio R corresponds to a ratio of the first coolant flow rate QF 1  and the second coolant flow rate QF 2 . 
     As shown in  FIG. 6 , the first coolant flow rate QF 1  when the rotational speed N is lower than a first rotational speed N 1  is greater than the first coolant flow rate QF 1  when the rotational speed N is equal to or higher than the first rotational speed N 1 . That is, the first coolant flow rate QF 1  is relatively large in the low-speed region, and the first coolant flow rate QF 1  is relatively small in the high-speed region. It is thus possible to effectively cool the high-temperature inverter  100 -stator  210  pair in the low-speed region and to save the first coolant CL 1  in the high-speed region. That is, it is possible to efficiently cool the inverter  100  and the stator  210 . 
     On the other hand, the second coolant flow rate QF 2  when the rotational speed N is equal to or higher than a second rotational speed N 2  is greater than the second coolant flow rate QF 2  when the rotational speed N is lower than the second rotational speed N 2 . That is, the second coolant flow rate QF 2  is relatively large in the high-speed region, and the second coolant flow rate QF 2  is relatively small in the low-speed region. It is thus possible to effectively cool the high-temperature rotor  220  in the high-speed region and to save the second coolant CL 2  in the low-speed region. That is, it is possible to efficiently cool the rotor  220 . 
     Typically, a magnitude relationship between the first coolant flow rate QF 1  and the second coolant flow rate QF 2  is reversed between the low-speed region and the high-speed region. For example, when the rotational speed N is a third rotational speed, the first coolant flow rate QF 1  is equal to the second coolant flow rate QF 2 . When the rotational speed N is lower than the third rotational speed, the first coolant flow rate QF 1  is greater than the second coolant flow rate QF 2 . On the other hand, when the rotational speed N is higher than the third rotational speed, the second coolant flow rate QF 2  is greater than the first coolant flow rate QF 1 . It is thus possible to cool the inverter  100 -stator  210  pair and the rotor  220  in a well-balanced manner. 
     In the example shown in  FIG. 6 , the first coolant flow rate QF 1  decreases as the rotational speed N increases, and the second coolant flow rate QF 2  increases as the rotational speed N increases. However, the first coolant flow rate QF 1  and the second coolant flow rate QF 2  need not necessarily change monotonically. For example, as shown in  FIG. 7 , the first coolant flow rate QF 1  and the second coolant flow rate QF 2  may change in a step-by-step manner. 
     The distribution structure  30  changes the distribution ratio R, that is, the first coolant flow rate QF 1  and the second coolant flow rate QF 2 , according to the rotational speed N of the rotor  220 .  FIG. 8  shows a configuration example of the distribution structure  30  according to the present embodiment. The controller  32  holds a map indicating the relationship as exemplified in  FIGS. 6 and 7 . A rotational speed sensor  34  detects the rotational speed N of the rotor  220 . The controller  32  receives information on the rotational speed N of the rotor  220  from the rotational speed sensor  34 . The controller  32  calculates a target distribution ratio based on the map and the rotational speed N, and controls the distributor  31  such that the target distribution ratio is achieved. 
     As described above, according to the second embodiment, the heat generation characteristics depending on the rotational speed N of the rotor  220  are taken into consideration. When the rotational speed N is low, the heat generations in the inverter  100  and the stator  210  become large. On the other hand, when the rotational speed N is high, the heat generation in the rotor  220  becomes large. Changing the distribution ratio R of the first coolant CL 1  and the second coolant CL 2  according to the rotational speed N makes it possible to further efficiently cool the inverter  100 , the stator  210 , and the rotor  220 . 
     3. Third Embodiment 
     In the third embodiment, another example of the distribution structure  30  will be described. Descriptions overlapping with the above-described embodiments will be omitted as appropriate. 
       FIG. 9  is a schematic diagram showing a configuration example of the distribution structure  30  according to the third embodiment.  FIG. 9  mainly shows a configuration of the rotor  220 . The configuration of the rotor  220  is the same as that described in  FIG. 4 . However, the distributor  31  as shown in  FIG. 5  is not provided at the branch point BR. 
     As described above, the rotor core flow path FP 22  extends from the downstream end of the rotor shaft flow path FP 21  toward the inside of the rotor core  222 . This means that the extending direction of at least a portion of the rotor core flow path FP 22  has an R-direction component. In the example shown in  FIG. 9 , the rotor core flow path FP 22 - 1  extends in the R-direction. When the rotor  220  rotates, a centrifugal force acts on the second coolant CL 2  present in the portion having the R-direction component. The centrifugal force promotes the discharge of the second coolant CL 2  from the rotor core flow path FP 22  to the outside of the rotor core  222 . As the discharge of the second coolant CL 2  is promoted, drawing of the second coolant CL 2  from the common flow path FPC into the second flow path FP 2  is promoted. That is to say, when the rotor  220  rotates, the drawing of the second coolant CL 2  into the second flow path FP 2  due to a negative pressure is promoted. 
     The centrifugal force and the negative pressure increase as the rotational speed N of the rotor  220  increases. Therefore, as the rotational speed N of the rotor  220  increases, the amount of the drawing of the second coolant CL 2  from the common flow path FPC into the second flow path FP 2  increases. That is, the second coolant flow rate QF 2  increases. When the amount of the drawing of the second coolant CL 2  from the common flow path FPC into the second flow path FP 2  increases, the first coolant CL 1  distributed from the common flow path FPC to the first flow path FP 1  decreases accordingly. That is, the first coolant flow rate QF 1  decreases. 
     As described above, as the rotational speed N of the rotor  220  increases, the second coolant flow rate QF 2  is automatically increased, and the first coolant flow rate QF 1  is automatically decreased. In other words, the relationship as exemplified in the above  FIG. 6  is automatically achieved. A desired relationship can be obtained by appropriately designing a length and a diameter of each portion (i.e., the connection flow path FP 20 , the rotor shaft flow path FP 21 , and the rotor core flow path FP 22 ) of the second flow path FP 2 . 
     The distribution structure  30  distributes the coolant CL flowing through the common flow path FPC to the first flow path FP 1  and the second flow path FP 2 , and changes the distribution ratio R of the first coolant CL 1  and the second coolant CL 2 . In the third embodiment, the branch point BR, the second flow path FP 2 , and the rotor  220  correspond to such the distribution structure  30 . 
     As described above, according to the third embodiment, the change in the distribution ratio R depending on the rotational speed N of the rotor  220  is automatically achieved due to the structure of the second flow path FP 2  arranged inside the rotor  220 . The distributor  31  and the controller  32  as shown in the above  FIG. 5  are unnecessary. Therefore, the structure of the cooling device  10  is simplified, and a manufacturing cost is also reduced. 
     4. Fourth Embodiment 
       FIG. 10  is a schematic diagram showing a configuration example of the motor  200 , the first flow path FP 1 , and the second flow path FP 2  according to a fourth embodiment. Descriptions overlapping with the above-described embodiments will be omitted as appropriate. 
     As shown in  FIG. 10 , the second flow path FP 2  further includes a rotor shaft flow path FP 23  branching from the rotor shaft flow path FP 21 . The rotor shaft flow path FP 23  extends in the R-direction from the rotor shaft flow path FP 21  toward the outside of the rotor shaft  221 . An external opening of the rotor shaft flow path FP 23  is directed to the stator coil  211 . 
     A second coolant CL 2 ′ being a part of the second coolant CL 2  flowing through the rotor shaft flow path FP 21  is discharged from the rotor shaft flow path FP 23  toward the stator coil  211 . The second coolant CL 2 ′ supplementarily cools the stator coil  211 . This further improves the cooling efficiency of the stator coil  211 . 
     5. Fifth Embodiment 
       FIG. 11  is a schematic diagram showing a configuration example of the cooling device  10  according to a fifth embodiment. Descriptions overlapping with the above-described embodiments will be omitted as appropriate. 
     A battery  300  of the vehicle  1  supplies power to the inverter  100 , for example. The flow path FP of the cooling device  10  further includes a third flow path FP 3  for cooling the battery  300 . The third flow path FP 3  branches from the common flow path FPC. A third coolant CL 3  out of the coolant CL flowing through the common flow path FPC is distributed to the third flow path FP 3 . The battery  300  is cooled by the third coolant CL 3 . 
     According to the fifth embodiment, it is possible to efficiently cool the inverter  100 , the motor  200 , and the battery  300 . 
     The third flow path FP 3  may branch from the first flow path FP 1  or the second flow path FP 2 . In other words, the first flow path FP 1  and the second flow path FP 2  may branch from the common flow path FPC at different branch points, respectively.