Patent Publication Number: US-2020292053-A1

Title: Vehicle lubrication structure and vehicle lubrication control method

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2019-048787 filed on Mar. 15, 2019 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a vehicle lubrication structure and a vehicle lubrication control method. 
     2. Description of Related Art 
     Japanese Unexamined Patent Application Publication No. 2008-279826 (JP 2008-279826 A) discloses a vehicle driving apparatus in which seizure to be caused by deficiency of oil supply can be prevented and a decrease in fuel efficiency can be suppressed by reducing a stirring resistance of oil in a driving force transmission apparatus due to excessive supply of oil. 
     SUMMARY 
     In the vehicle driving apparatus disclosed in JP 2008-279826 A, the oil level in a case is reduced by supplying and storing, in a catch tank, oil stored at the bottom of the case. Therefore, if the amount of oil stored in the catch tank increases, oil suppliable to the driving force transmission apparatus or a rotating electrical machine may be insufficient. 
     The present disclosure provides a vehicle lubrication structure and a vehicle lubrication control method in which deficiency of oil to be supplied to a driving force transmission apparatus and a rotating electrical machine can be suppressed while reducing a stirring resistance of oil in the driving force transmission apparatus. 
     A vehicle lubrication structure according to a first aspect of the present disclosure includes a rotating electrical machine, a driving force transmission apparatus, a first reservoir, a second reservoir, a first oil path, a second oil path, and an electric oil pump. The first reservoir is configured to store oil. The second reservoir is configured to store the oil, and has a capacity smaller than a capacity of the first reservoir. The first oil path connects the first reservoir to the second reservoir. The second oil path connects the second reservoir to the driving force transmission apparatus and the rotating electrical machine. The second oil path includes branch oil paths for supplying the oil to the driving force transmission apparatus and the rotating electrical machine, respectively. The electric oil pump is configured to supply the oil stored in the first reservoir to the driving force transmission apparatus and the rotating electrical machine. The electric oil pump is provided in the first oil path or the second oil path. 
     In the vehicle lubrication structure according to the first aspects of the present disclosure, the oil stored in the first reservoir can be supplied to and stored in the second reservoir by operating the electric oil pump. Further, the amount of the oil to be supplied from the second reservoir to the driving force transmission apparatus and the rotating electrical machine can be controlled by controlling the amount of the oil to be supplied from the first reservoir to the second reservoir. Thus, the oil level in the first reservoir can be reduced, and the stirring resistance in the driving force transmission apparatus can be reduced. If oil supply is necessary, deficiency of the oil to be supplied to the driving force transmission apparatus and the rotating electrical machine can be suppressed while suppressing an increase in the oil level in the first reservoir due to return oil, which returns to the first reservoir after being supplied to the driving force transmission apparatus and the rotating electrical machine. Thus, the vehicle lubrication structure and the vehicle lubrication control method according to the first and second aspects of the present disclosure attain such effects that the deficiency of the oil to be supplied to the driving force transmission apparatus and the rotating electrical machine can be suppressed while reducing the stirring resistance in the driving force transmission apparatus. 
     In the vehicle lubrication structure according to the first aspect of the present disclosure, the second reservoir may be provided above a static oil level of the oil stored in the first reservoir. 
     In the vehicle lubrication structure according to the first aspect of the present disclosure, an increase in the oil level in the first reservoir can be suppressed and an increase in the stirring resistance can be suppressed because the amount of the oil stored in the second reservoir increases. 
     The vehicle lubrication structure according to the first aspect of the present disclosure may further include a check valve configured to prevent backflow of the oil from the second reservoir to the first reservoir. 
     In the vehicle lubrication structure according to the first aspect of the present disclosure, it is possible to suppress an increase in the oil level in the first reservoir due to the backflow of the oil from the second reservoir arranged above the static oil level of the oil stored in the first reservoir. Further, it is possible to reduce the occurrence of a case where lubrication is hindered by the backflow of the oil from the second reservoir to the first reservoir. 
     The vehicle lubrication structure according to the first aspect of the present disclosure may further include a case that houses the first reservoir. The second reservoir may be arranged outside the case. 
     In the vehicle lubrication structure according to the first aspect of the present disclosure, the second reservoir can be provided irrespective of the static oil level of the oil stored in the first reservoir. 
     The vehicle lubrication structure according to the first aspect of the present disclosure may further include an oil cooler configured to cool the oil. The second reservoir may be constructed integrally with the oil cooler. 
     In the vehicle lubrication structure according to the first aspect of the present disclosure, there is no need to construct the second reservoir as a separate member. Thus, the structure can be simplified. 
     In a vehicle lubrication control method for a vehicle according to a second aspect of the present disclosure, the vehicle includes a rotating electrical machine, a driving force transmission apparatus, a first reservoir, a second reservoir, a first oil path, a second oil path, an electric oil pump, and a controller. The first reservoir is configured to store oil. The second reservoir is configured to store the oil, and has a capacity smaller than a capacity of the first reservoir. The first oil path connects the first reservoir to the second reservoir. The second oil path connects the second reservoir to the driving force transmission apparatus and the rotating electrical machine. The second oil path includes branch oil paths for supplying the oil to the driving force transmission apparatus and the rotating electrical machine, respectively. The electric oil pump is provided in the first oil path or the second oil path. The electric oil pump is configured to supply the oil stored in the first reservoir to the driving force transmission apparatus and the rotating electrical machine. The controller is configured to control the electric oil pump. The vehicle lubrication control method includes receiving, by the controller, a signal indicating a request to start a vehicle system, and operating the electric oil pump for a constant time after receiving, by the controller, the signal indicating the request to start the vehicle system. 
     In the vehicle lubrication control method according to the second aspect of the present disclosure, when the vehicle starts to travel in a state in which the vehicle is completely stopped, the vehicle can start to travel after the second reservoir is filled with the oil by operating the electric oil pump for the constant time. Thus, it is possible to reduce a loss of time to lubricate the driving force transmission apparatus and the rotating electrical machine when the vehicle starts to travel. 
     The vehicle lubrication control method according to the second aspect of the present disclosure may further include operating the electric oil pump by the controller for the constant time when an operation stop time of the electric oil pump is equal to or longer than a predetermined time. 
     In the vehicle lubrication control method according to the second aspect of the present disclosure, when the vehicle starts to travel in a state in which the vehicle speed is zero and when the operation stop time of the electric oil pump is equal to or longer than the predetermined time, the vehicle can start to travel after the second reservoir is filled with the oil by operating the electric oil pump for the constant time. Thus, it is possible to reduce a loss of time to lubricate the driving force transmission apparatus and the rotating electrical machine when the vehicle starts to travel in the state in which the vehicle speed is zero. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a diagram illustrating the schematic configuration of an electric vehicle according to an embodiment; 
         FIG. 2  is a diagram illustrating an example of a vehicle lubrication structure according to the embodiment; 
         FIG. 3  is a sectional view of an oil cooler provided in the electric vehicle according to the embodiment; 
         FIG. 4  is a sectional view of an oil cooler of a comparative example; 
         FIG. 5  is a diagram illustrating a case where the oil cooler is provided such that at least a part of the oil cooler is positioned below a static oil level in a first reservoir; 
         FIG. 6  is a diagram illustrating a case where the oil cooler is provided so as to be positioned above the static oil level in the first reservoir; 
         FIG. 7  is a diagram illustrating a vehicle lubrication structure in a case where a check valve is provided to prevent backflow of oil from a second reservoir to the first reservoir; 
         FIG. 8  is a flowchart illustrating an example of control over an electric oil pump to be performed when the vehicle starts to travel in a state in which the vehicle is completely stopped; 
         FIG. 9  is a flowchart illustrating an example of control over the electric oil pump to be performed when the vehicle starts to travel in a state in which the vehicle speed is zero; 
         FIG. 10  is a diagram illustrating a vehicle lubrication structure in a case where an oil reservoir is provided on an upstream side of the oil cooler; 
         FIG. 11  is a diagram illustrating a vehicle lubrication structure in a case where the oil reservoir is provided on a downstream side of the oil cooler; 
         FIG. 12  is a diagram illustrating a vehicle lubrication structure in a case where the electric oil pump is provided on the downstream side of the oil cooler; 
         FIG. 13  is a diagram illustrating a vehicle lubrication structure in a case where electric oil pumps are provided in branch oil paths for supplying oil to a speed reducing mechanism and a differential, respectively; 
         FIG. 14  is a sectional view of an oil cooler provided with an oil reservoir below a heat exchanger; 
         FIG. 15  is a sectional view of an oil cooler provided with an oil reservoir above a heat exchanger; 
         FIG. 16  is a diagram illustrating a case where an oil path is provided in the vicinity of a motor; and 
         FIG. 17  is a diagram illustrating an example of a lubrication structure for a hybrid vehicle. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A vehicle lubrication structure and a vehicle lubrication control method according to an embodiment of the present disclosure are described below. This embodiment is not intended to limit the applicable embodiment. For example, an electric vehicle is not limited to an electric vehicle including only a rotating electrical machine such as a motor as a traveling drive source. The electric vehicle includes a hybrid vehicle including an engine such as an internal combustion engine and a rotating electrical machine such as a motor as traveling drive sources. 
       FIG. 1  is a diagram illustrating the overall configuration of an electric vehicle  1  according to the embodiment. The electric vehicle  1  includes an electronic controller  2 , an electric storage device  3 , an inverter  4 , a rotating electrical machine  10 , a speed reducing mechanism  21 , a differential  22 , a pair of drive shafts  23 , a pair of driving wheels  24 , an electric oil pump  30 , a transaxle case  40 , a start switch  51 , an accelerator pedal  52 , a brake pedal  53 , and a vehicle speed sensor  54 . In the electric vehicle  1  according to the embodiment, the rotating electrical machine  10 , the speed reducing mechanism  21 , the differential  22 , and the electric oil pump  30  are arranged in the transaxle case  40  that is a common housing. 
     The electronic controller  2  determines a target drive torque of the rotating electrical machine  10  based on, for example, conditions of the accelerator pedal  52  and the brake pedal  53  operated by a driver and a vehicle speed acquired by the vehicle speed sensor  54 . The electronic controller  2  commands the inverter  4  based on the determined target drive torque. The commanded inverter  4  converts direct-current power of the electric storage device  3  into alternating-current power based on the target drive torque, and transmits the alternating-current power to the rotating electrical machine  10 . Examples of the electric storage device  3  include a secondary battery such as a nickel-metal hydride battery or a lithium ion battery, and a capacitor. An output torque of the rotating electrical machine  10  is transmitted to the pair of driving wheels  24  via the speed reducing mechanism  21 , the differential  22 , and the pair of drive shafts  23  to achieve the target drive torque. The speed reducing mechanism  21  and the differential  22  are constituted by a plurality of gears to constitute a driving force transmission apparatus. In the electric vehicle  1  according to the embodiment, the traveling drive source is the rotating electrical machine  10  only, and therefore the output torque of the rotating electrical machine  10  corresponds to a drive torque of the vehicle. 
     The start switch  51  is an input device to be used by the driver to perform a “READY ON” operation or a “READY OFF” operation. By operating the start switch  51 , a signal indicating that the start switch  51  is operated is transmitted to the electronic controller  2 . The “READY ON” operation is an operation for bringing the electric vehicle  1  into a “READY ON” state (travelable state) by starting a vehicle system (device for causing the electric vehicle  1  to travel). The “READY OFF” operation is an operation for bringing the electric vehicle  1  into a “READY OFF” state (untravelable state) by stopping the vehicle system. When the signal indicating that the start switch  51  is operated is received in the “READY OFF” state, the electronic controller  2  brings the electric vehicle  1  into the “READY ON” state. When the signal indicating that the start switch  51  is operated is received in the “READY ON” state, the electronic controller  2  brings the electric vehicle  1  into the “READY OFF” state. 
       FIG. 2  is a diagram illustrating an example of a lubrication structure for the electric vehicle  1  according to the embodiment. In the lubrication structure for the electric vehicle  1  according to the embodiment, an oil pan  41 , a strainer  42 , the rotating electrical machine  10 , the speed reducing mechanism  21 , the differential  22 , and the electric oil pump  30  are provided inside the transaxle case  40 . Further, an oil cooler  60  is provided outside the transaxle case  40  to cool oil. 
     The oil pan  41  together with the bottom of the transaxle case  40  constitutes a first reservoir  101  configured to store oil. Oil supply from the oil pan  41  to the oil cooler  60  via the strainer  42  is performed through a first oil path constituted by a pipe  81 . The electric oil pump  30  is provided midway along the pipe  81  that constitutes the first oil path. In the electric vehicle  1  according to the embodiment, the oil cooler  60  is arranged in an oil path which supplies oil to the rotating electrical machine  10 . Oil supply from the oil cooler  60  to the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  is performed through a second oil path constituted by a plurality of pipes such as a pipe  82  to a pipe  88  connecting the oil cooler  60  to the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22 . 
     The second oil path is constituted by the pipe  82  coupled to the oil cooler  60 , the pipes  83  and  86  branching from the pipe  82 , the pipes  84  and  85  branching from the pipe  83 , and the pipes  87  and  88  branching from the pipe  86 . The pipe  84  constitutes a branch oil path for supplying oil to the speed reducing mechanism  21 . The pipe  85  constitutes a branch oil path for supplying oil to the differential  22 . The pipes  87  and  88  constitute a branch oil path for supplying oil to the rotating electrical machine  10 . 
     By operating the electric oil pump  30 , the oil stored in the first reservoir  101  is forcibly supplied to the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22 . The amount of oil to be supplied to the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  is adjustable by changing power of the electric oil pump  30 . 
       FIG. 3  is a sectional view of the oil cooler  60  provided in the electric vehicle  1  according to the embodiment. As illustrated in  FIG. 3 , the oil cooler  60  provided in the electric vehicle  1  according to the embodiment includes a heat exchanger  601  in which a plurality of oil channels  610  and a plurality of coolant channels  620  are alternately stacked in a height direction. In the heat exchanger  601 , oil flowing through the oil channel  610  exchanges heat with a coolant flowing through the coolant channel  620 , thereby cooling the oil. 
       FIG. 4  is a sectional view of an oil cooler  60 A of a comparative example. As illustrated in  FIG. 4 , the oil cooler  60 A of the comparative example includes a heat exchanger  601 A in which a plurality of oil channels  610 A and a plurality of coolant channels  620 A are alternately stacked in a height direction. In the oil cooler  60 A of the comparative example, a plurality of fins  611 A are provided in the oil channels  610 A, and a plurality of embossments  621 A are provided in the coolant channels  620 A. 
     The height, width, and length of the oil channel  610  of the oil cooler  60  provided in the electric vehicle  1  according to the embodiment are larger than the height, width, and length of the oil channel  610 A of the oil cooler  60 A of the comparative example. That is, the capacity of the oil channel  610  is larger than the capacity of the oil channel  610 A. No embossment is provided in the coolant channel  620 , and therefore the capacity of the coolant channel  620  is larger, by an amount corresponding to embossments, than the coolant channel  620 A provided with the embossments  621 A. 
     Thus, in the oil cooler  60  provided in the electric vehicle  1  according to the embodiment, the heat exchange performance is equal to that of the oil cooler  60 A of the comparative example, and a pressure loss in the oil channel  610  is greatly smaller than that of the oil cooler  60 A. A large amount of oil can be stored in the oil cooler  60 , and therefore the oil cooler  60  of the electric vehicle  1  according to the embodiment functions as a second reservoir  102  configured to store oil separately from the first reservoir  101 . By constructing the second reservoir  102  integrally with the oil cooler  60 , there is no need to construct the second reservoir  102  as a separate member. Thus, the structure can be simplified. 
     The amount of oil that can be stored in the oil cooler  60  provided in the electric vehicle  1  according to the embodiment in  FIG. 3  is 1000 [ml] to 2000 [ml]. The amount of oil that can be stored in the oil cooler  60 A of the comparative example in  FIG. 4  is 300 [ml] to 600 [ml]. 
     In the lubrication structure for the electric vehicle  1  according to the embodiment, the oil stored in the first reservoir  101  can be supplied to and stored in the second reservoir  102  by operating the electric oil pump  30 . Further, the amount of oil to be supplied from the second reservoir  102  to the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  can be controlled by controlling the amount of oil to be supplied from the first reservoir  101  to the second reservoir  102 . Thus, the oil level in the first reservoir  101  can be reduced, and the stirring resistance in each of the speed reducing mechanism  21  and the differential  22  can be reduced. if oil supply is necessary, deficiency of oil to be supplied to the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  can be suppressed while suppressing an increase in the oil level in the first reservoir  101  due to return oil. The return oil is oil that returns to the first reservoir  101  after being supplied to the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22 . Thus, in the lubrication structure for the electric vehicle  1  according to the embodiment, the deficiency of oil to be supplied to the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  can be suppressed while reducing the stirring resistance in each of the speed reducing mechanism  21  and the differential  22 . 
     In the electric vehicle  1  according to the embodiment, as illustrated in  FIG. 5 , the oil cooler  60  is provided such that at least a part of the oil cooler  60  is positioned below a static oil level LV in the first reservoir  101  constituted by the oil pan  41  (not illustrated). The static oil level LV refers to an oil level in a state in which the oil cooler  60  is not filled with oil. Therefore, the oil level of the oil stored in the oil cooler  60  can be made substantially equal to the static oil level LV even if the operation of the electric oil pump  30  is stopped due to, for example, a stop of the electric vehicle  1 . Thus, it is possible to prevent the occurrence of a case where the oil in the oil cooler  60  runs short due to backflow of the oil from the oil cooler  60  to the oil pan  41 . When oil is supplied from the oil pan  41  to the oil cooler  60  by operating the electric oil pump  30  through the start of traveling of the electric vehicle  1 , for example, the oil cooler  60  can quickly be filled with oil because oil is prestored in the oil cooler  60 . Thus, it is possible to reduce a loss of time to lubricate the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22 . 
     In the electric vehicle  1  according to the embodiment, as illustrated in  FIG. 6 , the oil cooler  60  may be provided such that the oil cooler  60  is positioned above the static oil level LV of the oil stored in the oil pan  41  (not illustrated). Therefore, an increase in the oil level of the oil stored in the oil pan  41  can be suppressed by increasing the amount of oil stored in the oil cooler  60  increases. Thus, it is possible to suppress an increase in the stirring resistance when the oil stored in the oil pan  41  is stirred by the differential  22  or the like. 
     If the oil cooler  60  is provided so as to be positioned above the static oil level LV in the oil pan  41 , it is preferable as illustrated in  FIG. 7  that a check valve  70  configured to prevent backflow of oil from the oil cooler  60  to the oil pan  41  be provided midway along the pipe  81  that constitutes the first oil path. Since the check valve  70  prevents the backflow of oil from the oil cooler  60  to the oil pan  41 , it is possible to suppress an increase in the oil level of the oil stored in the oil pan  41  due to the backflow of oil from the oil cooler  60 . Thus, it is possible to suppress the increase in the stirring resistance when the oil stored in the oil pan  41  is stirred by the differential  22  or the like. Further, it is possible to reduce the occurrence of a case where lubrication of the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  is hindered by the backflow of oil from the oil cooler  60  to the oil pan  41 . 
       FIG. 8  is a flowchart illustrating an example of control over the electric oil pump  30  to be performed when the vehicle starts to travel in a state in which the vehicle is completely stopped. 
     First, the electronic controller  2  brings the electric vehicle  1  into the “READY ON” state when a signal indicating that the start switch  51  is operated by the driver (signal indicating a request to start the vehicle system) is received in the “READY OFF” state (Step S 1 ). Next, the electronic controller  2  starts to operate the electric oil pump  30  (turns ON the operation of the electric oil pump  30 ) (Step S 2 ), and operates the electric oil pump  30  for several seconds as a constant time (Step S 3 ). Then, the electronic controller  2  starts traveling of the electric vehicle  1  in response to an operation of the accelerator pedal  52  by the driver or the like (Step S 4 ). 
     When the vehicle starts to travel in the state in which the vehicle is completely stopped, the electric vehicle  1  can start to travel after the oil cooler  60  is filled with oil by operating the electric oil pump  30  for several seconds as the constant time. Thus, it is possible to reduce a loss of time to lubricate the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  when the vehicle starts to travel. 
       FIG. 9  is a flowchart illustrating an example of control over the electric oil pump  30  to be performed when the vehicle starts to travel in a state in which the vehicle speed is zero. 
     First, the electronic controller  2  determines that the electric vehicle  1  is stopped when a signal indicating that the vehicle speed is zero is received from the vehicle speed sensor  54  (Step  11 ). Next, the electronic controller  2  stops the operation of the electric oil pump  30  (turns OFF the operation of the electric oil pump  30 ) (Step S 12 ). Next, the electronic controller  2  determines whether an OFF time T, which is an operation stop time of the electric oil pump  30 , is shorter than a predetermined time T 1  (Step S 13 ). When determination is made that the OFF time T is shorter than the predetermined time T 1  (Yes in Step S 13 ), the electronic controller  2  keeps the operation of the electric oil pump in the OFF state (Step S 14 ), and determines whether the vehicle starts to travel (Step S 15 ). 
     When determination is made that the vehicle starts to travel in response to an operation in which the driver stops depressing the brake pedal  53  or depresses the accelerator pedal  52  (Yes in Step S 15 ), the electronic controller  2  terminates the control over the electric oil pump  30 , which is performed when the vehicle starts to travel in the state in which the vehicle speed is zero. When determination is made that the vehicle does not start to travel in response to an operation in which the driver keeps depressing the brake pedal  53  (No in Step S 15 ), the electronic controller  2  returns to the processing of Step S 13 . 
     When determination is made in the processing of Step S 13  that the OFF time T is equal to or longer than the predetermined time T 1  (No in Step S 13 ), the electronic controller  2  starts to operate the electric oil pump  30  (turns ON the operation of the electric oil pump  30 ) (Step S 16 ), and operates the electric oil pump  30  for several seconds as the constant time (Step S 17 ). Next, the electronic controller  2  stops the operation of the electric oil pump  30  (turns OFF the operation of the electric oil pump  30 ), and resets the OFF time T (Step S 18 ). 
     Next, the electronic controller  2  determines whether the vehicle starts to travel (Step S 15 ). When determination is made that the vehicle starts to travel in response to an operation in which the driver stops depressing the brake pedal  53  or depresses the accelerator pedal  52  (Yes in Step S 15 ), the electronic controller  2  terminates the control over the electric oil pump  30 , which is performed when the vehicle starts to travel in the state in which the vehicle speed is zero. When determination is made that the vehicle does not start to travel in response to an operation in which the driver keeps depressing the brake pedal  53  (No in Step S 15 ), the electronic controller  2  returns to the processing of Step S 13 . 
     When the vehicle starts to travel in the state in which the vehicle speed is zero and when the OFF time T of the electric oil pump  30  is equal to or longer than the predetermined time T 1 , the electric vehicle  1  can start to travel after the oil cooler  60  is filled with oil by operating the electric oil pump  30  for several seconds as the constant time. Thus, it is possible to reduce a loss of time to lubricate the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  when the vehicle starts to travel in the state in which the vehicle speed is zero. 
       FIG. 10  is a diagram illustrating a lubrication structure for the electric vehicle  1  in a case where an oil reservoir  90  is provided on an upstream side of the oil cooler  60 .  FIG. 11  is a diagram illustrating a vehicle lubrication structure in a case where the oil reservoir  90  is provided on a downstream side of the oil cooler  60 . In the electric vehicle  1  according to the embodiment, as illustrated in  FIG. 10 , the oil reservoir  90  that constitutes the second reservoir  102  may be provided as a separate member from the oil cooler  60  on the upstream side of the oil cooler  60  and midway along the pipe  81  that constitutes the first oil path. As illustrated in  FIG. 11 , the oil reservoir  90  that constitutes the second reservoir  102  may be provided as a separate member from the oil cooler  60  on the downstream side of the oil cooler  60  and midway along the pipe  82  that constitutes the second oil path. By providing the oil reservoir  90  that constitutes the second reservoir  102  outside the oil cooler  60  as a separate member from the oil cooler  60 , the degree of freedom increases in terms of the capacity of the second reservoir  102 . More oil is stored in the oil reservoir  90  that constitutes the second reservoir  102  than the case where oil is stored by using only the heat exchanger  601  of the oil cooler  60  as the second reservoir  102 . Thus, the static oil level LV of the oil stored in the oil pan  41  can be reduced. Accordingly, the stirring resistance of oil due to the differential  22  or the like can be reduced, and the deficiency of oil to be supplied to the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  can be suppressed. 
     In the electric vehicle  1  according to the embodiment, one or more electric oil pumps  30  may be provided in the second oil path on a downstream side of the second reservoir  102  instead of the first oil path connecting the first reservoir  101  to the second reservoir  102 . 
       FIG. 12  is a diagram illustrating a lubrication structure for the electric vehicle  1  in a case where the electric oil pump  30  is provided on the downstream side of the oil cooler  60 . In the electric vehicle  1  according to the embodiment, as illustrated in  FIG. 12 , the electric oil pump  30  may be provided on the downstream side of the oil cooler  60  and midway along the pipe  82  that constitutes the second oil path. 
       FIG. 13  is a diagram illustrating a lubrication structure for the electric vehicle  1  in a case where electric oil pumps  30 A and  30 B are provided in the branch oil paths for supplying oil to the speed reducing mechanism  21  and the differential  22 , respectively. In the electric vehicle  1  according to the embodiment, as illustrated in  FIG. 13 , the electric oil pumps  30 A and  30 B may be provided on the downstream side of the oil cooler  60  and midway along the pipes  84  and  85  that constitute the second oil path and also constitute the branch oil paths for supplying oil to the speed reducing mechanism  21  and the differential  22 , respectively. By providing the electric oil pumps  30 A and  30 B midway along the pipes  84  and  85  for supplying oil to the speed reducing mechanism  21  and the differential  22 , respectively, power of the electric oil pump  30 A and power of the electric oil pump  30 B are changed such that the amounts of oil to be supplied to the speed reducing mechanism  21  and the differential  22  can be adjusted. Thus, appropriate amounts of oil can be supplied to the speed reducing mechanism  21  and the differential  22 , and a drag loss of oil in the speed reducing mechanism  21  and the differential  22  can further be reduced. 
       FIG. 14  is a sectional view of an oil cooler  60 B provided with an oil reservoir  602 B below a heat exchanger  601 B. In the electric vehicle  1  according to the embodiment, the oil cooler  60 B including the heat exchanger  601 B and the oil reservoir  602 B as illustrated in  FIG. 14  may be used as the second reservoir  102  in place of the oil cooler  60  having the internal structure illustrated in  FIG. 3 . 
     The heat exchanger  601 B is configured such that a plurality of oil channels  610 B and a plurality of coolant channels  620 B are alternately stacked in a height direction. The oil reservoir  602 B having a reservoir space  630 B configure to store oil is provided below the heat exchanger  601 B. The reservoir space  630 B communicates with a lowermost oil channel  610 B of the heat exchanger  601 B. 
     As indicated by an arrow A 1  in  FIG. 14 , oil sent from the oil pan  41  to the oil cooler  60 B by the electric oil pump  30  is supplied into the reservoir space  630 B from the bottom of the oil reservoir  602 B. After the reservoir space  630 B is filled with the oil, the oil is supplied from the reservoir space  630 B to the oil channel  610 B of the heat exchanger  601 B. Through the plurality of oil channels  610 B, the oil is discharged from the top of the heat exchanger  601 B as indicated by an arrow A 2  in  FIG. 14 . 
     By providing the oil reservoir  602 B having the dedicated reservoir space  630 B configured to store oil in the oil cooler  60 B as the oil cooler  60 B illustrated in  FIG. 14 , more oil can be stored in the oil cooler  60 B than the case where oil is stored only in the oil channels  610  of the heat exchanger  601  of the oil cooler  60 . Thus, as compared to the use of the oil cooler  60 , the static oil level LV of the oil stored in the oil pan  41  can further be reduced with the same amount of oil as that in the case where the oil cooler  60  is used. Accordingly, the stirring resistance of oil due to the differential  22  or the like can be reduced, and the deficiency of oil to be supplied to the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  can be suppressed. 
       FIG. 15  is a sectional view of an oil cooler  60 C provided with an oil reservoir  602 C above a heat exchanger  601 C. In the electric vehicle  1  according to the embodiment, the oil cooler  60 C including the heat exchanger  601 C and the oil reservoir  602 C as illustrated in  FIG. 15  may be used as the second reservoir  102  in place of the oil cooler  60  having the internal structure illustrated in  FIG. 3 . 
     The heat exchanger  601 C is configured such that a plurality of oil channels  610 C and a plurality of coolant channels  620 C are alternately stacked in a height direction. The oil reservoir  602 C having a reservoir space  630 C configured to store oil is provided above the heat exchanger  601 C. The reservoir space  630 C communicates with an uppermost oil channel  610 C of the heat exchanger  601 C. 
     As indicated by an arrow A 3  in  FIG. 15 , oil sent from the oil pan  41  to the oil cooler  60 C by the electric oil pump  30  is supplied to the oil channel  610 C from the bottom of the heat exchanger  601 C. Through the plurality of oil channels  610 C, the oil is supplied to the reservoir space  630 C of the oil reservoir  602 C, and is stored in the reservoir space  630 C. After the reservoir space  630 C is filled with the oil, the oil is discharged from the top of the oil reservoir  602 C as indicated by an arrow A 4  in  FIG. 15 . 
     By providing the oil reservoir  602 C having the dedicated reservoir space  630 C configured to store oil in the oil cooler  60 C as the oil cooler  60 C illustrated in  FIG. 15 , more oil can be stored in the oil cooler  60 C than the case where oil is stored only in the oil channels  610  of the heat exchanger  601  of the oil cooler  60 . Thus, as compared to the use of the oil cooler  60 , the static oil level LV of the oil stored in the oil pan  41  can further be reduced with the same amount of oil as that in the case where the oil cooler  60  is used. Accordingly, the stirring resistance of oil due to the differential  22  or the like can be reduced, and the deficiency of oil to be supplied to the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  can be suppressed. 
     Since the oil reservoir  602 C is provided above the heat exchanger  601 C, the oil stored in the oil reservoir  602 C is more unlikely to flow out of the oil cooler  60 C through the plurality of oil channels  610 C of the heat exchanger  601 C as compared to a case where the oil reservoir  602 C is provided below the heat exchanger  601 C. Therefore, the amount of oil in the oil reservoir  602 C is unlikely to decrease in a state in which the electric oil pump  30  is not operated. Thus, it is possible to reduce a loss of time to lubricate the rotating electrical machine  10 , the speed reducing mechanism  21 , and the differential  22  when the electric oil pump  30  is operated, for example, at the start of traveling of the vehicle. 
       FIG. 16  is a diagram illustrating a case where the oil path is provided in the vicinity of the rotating electrical machine  10 . Since the temperature of oil passing through the oil cooler  60  decreases, the temperature of oil supplied to the speed reducing mechanism  21  and the differential  22  decreases as well. As the temperature of oil decreases, the viscosity of oil increases. There is a possibility that the drag loss of oil in the speed reducing mechanism  21  and the differential  22  is exacerbated. 
     As illustrated in  FIG. 16 , the pipes  82 ,  83 ,  84 , and  85  that constitute the second oil path for supplying oil from the oil cooler  60  to the speed reducing mechanism  21  and the differential  22  are arranged in the vicinity of the rotating electrical machine  10 . Oil flowing through the pipes  82 ,  83 ,  84 , and  85  arranged in the vicinity of the rotating electrical machine  10  is warmed by heat generated by driving the rotating electrical machine  10 . Therefore, the viscosity of the oil flowing through the pipes  82 ,  83 ,  84 , and  85  is lower than the viscosity of oil cooled by the oil cooler  60 . Thus, it is possible to suppress the exacerbation of the drag loss of oil in the speed reducing mechanism  21  and the differential  22 . The pipes  82 ,  83 ,  84 , and  85  that constitute the second oil path for supplying oil from the oil cooler  60  to the speed reducing mechanism  21  and the differential  22  may be arranged at positions where the pipes  82 ,  83 ,  84 , and  85  are brought into contact with oil flowed out from the rotating electrical machine  10 . Since the oil supplied to the rotating electrical machine  10  and warmed by heat of the rotating electrical machine  10  is brought into contact with the pipes  82 ,  83 ,  84 , and  85 , the oil flowing through the pipes  82 ,  83 ,  84 , and  85  can be warmed. Thus, effects similar to those described above can be attained. 
     In this embodiment, description is given of the case where the present disclosure is applied to the lubrication structure for the electric vehicle  1  in which the traveling drive source is only the rotating electrical machine  10 . The present disclosure may also be applied to, for example, a lubrication structure for a hybrid vehicle including an engine and a rotating electrical machine as traveling drive sources. 
       FIG. 17  is a diagram illustrating an example of a lubrication structure for a hybrid vehicle  1 A. In the lubrication structure for the hybrid vehicle  1 A illustrated in  FIG. 17 , the oil pan  41 , the strainer  42 , rotating electrical machines  10 A and  10 B, the speed reducing mechanism  21 , the differential  22 , the electric oil pump  30 , and a planetary gear mechanism  25  are provided inside the transaxle case  40 , and the oil cooler  60  and an engine that is an internal combustion engine (not illustrated) are provided outside the transaxle case  40 . The oil pan  41  and the strainer  42  constitute the first reservoir  101 . The speed reducing mechanism  21  and the differential  22  constitute the driving force transmission apparatus. In the hybrid vehicle  1 A illustrated in  FIG. 17 , the engine and the rotating electrical machine  10 B are used as traveling drive sources. 
     Oil supply from the oil pan  41  to the oil cooler  60  via the strainer  42  is performed through a first oil path constituted by pipes  81  and  811 . The electric oil pump  30  is provided midway along the pipe  81  that constitutes the first oil path. Oil supply from the oil cooler  60  to the rotating electrical machines  10 A and  10 B, the speed reducing mechanism  21 , and the differential  22  is performed through a second oil path constituted by a plurality of pipes such as the pipe  82  to the pipe  88 . Oil supply from the oil pan  41  to the planetary gear mechanism  25  via the strainer  42  is performed through pipes  81  and  812 . 
     The pipes  811  and  812  branch from the pipe  81  on a downstream side of the electric oil pump  30  in the pipe  81  to constitute branch oil paths for supplying oil to the oil cooler  60  and the planetary gear mechanism  25 , respectively. The planetary gear mechanism  25  may be arranged on a downstream side or an upstream side of the oil cooler  60 . 
     The second oil path is constituted by the pipe  82  coupled to the oil cooler  60 , the pipes  83  and  86  branching from the pipe  82 , the pipes  84  and  85  branching from the pipe  83 , pipes  861  and  862  branching from the pipe  86 , pipes  871  and  881  branching from the pipe  861 , and pipes  872  and  882  branching from the pipe  862 . The pipe  84  constitutes a branch oil path for supplying oil to the speed reducing mechanism  21 . The pipe  85  constitutes a branch oil path for supplying oil to the differential  22 . The pipes  871  and  881  constitute a branch oil path for supplying oil to the rotating electrical machine  10 A. The pipe  872  and  882  constitute a branch oil path for supplying oil to the rotating electrical machine  10 B. 
     In the lubrication structure for the hybrid vehicle  1 A illustrated in  FIG. 17 , oil stored in the first reservoir  101  is supplied to the rotating electrical machines  10 A and  10 B, the speed reducing mechanism  21 , the differential  22 , and the planetary gear mechanism  25  by operating the electric oil pump  30 . 
     Also in the lubrication structure for the hybrid vehicle  1 A illustrated in  FIG. 17 , deficiency of oil to be supplied to the rotating electrical machines  10 A and  10 B, the speed reducing mechanism  21 , the differential  22 , and the planetary gear mechanism  25  can be suppressed while reducing the stirring resistance in each of the speed reducing mechanism  21  and the differential  22  by applying various types of configuration and control similar to those of the lubrication structure for the electric vehicle  1  described above.