Patent Publication Number: US-2023155445-A1

Title: Drive unit for series hybrid vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national stage application of International Application No. PCT/IB2020/000504, filed on May 22, 2020. 
    
    
     BACKGROUND 
     Technical Field 
     The present invention relates to a drive unit for a series hybrid vehicle. 
     Background Information 
     WO2015/098328A1 discloses a water-cooled electric motor in which a helical cooling passage is formed inside a housing in which a stator is fixed, and a coolant inlet provided at one end of the cooling passage and a coolant outlet provided at the other end open to the outer periphery of the housing. 
     SUMMARY 
     In a series hybrid vehicle equipped with two electric motors, one for power generation and the other for driving, the two electric motors are arranged in close proximity with the rotational axes parallel to each other in order to make a drive unit including the two electric motors more compact. If a cooling passage, which has the coolant inlet and the coolant outlet as in the above-described document, is applied to the two electric motors of a series hybrid vehicle, the cooling passage of one and the cooling passage of the other would be connected in series. That is, the coolant outlet of one electric motor is connected to the coolant inlet of the other electric motor. However, if the two electric motors are arranged with the rotational axes parallel, as described above, the coolant outlet of the one electric motor and the coolant inlet of the other electric motor are separated in the axial direction, resulting in a longer connecting passage to connect them and, hence, a larger drive unit. The longer cooling liquid passage also results in greater pressure loss. 
     Thus, an object of the present invention is to provide a drive unit that is compact and also able to suppress pressure loss in the cooling passage. 
     According to one aspect of the present invention, a drive unit for a series hybrid vehicle is provided that comprises a first electric motor for driving and a second electric motor for power generation. In this drive unit, a first cylindrical inner housing provided on the outer periphery of the stator of the first electric motor and a second cylindrical inner housing provided on the outer periphery of the stator of the second electric motor are each provided with a helical cooling passage on the respective outer peripheries, formed so as to surround each stator in helical fashion. The first electric motor and the second electric motor are housed in an outer housing such that the rotor axes are parallel, the helical cooling passage of the first electric motor and the helical cooling passage of the second electric motor are connected in series via a connecting passage, and the coolant outlet of the helical cooling passage on the upstream side to which one end of the connecting passage is connected and the coolant inlet of the helical cooling passage on the downstream side to which the other end of the connecting passage is connected are arranged at the end portions on the same side in the direction of the rotor axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the attached drawings which form a part of this original disclosure. 
         FIG.  1    is an external view of a drive unit according to an embodiment. 
         FIG.  2    is an external view of a drive unit according to a comparative example. 
         FIG.  3    is an exploded view of the drive unit according to the embodiment. 
         FIG.  4    is a view of the drive unit as seen from the rotor axis direction. 
         FIG.  5    is an external view of an inner housing. 
         FIG.  6    is a top view of an example of the arrangement of two inner housings. 
         FIG.  7    is a view of  FIG.  6    as seen from the direction of the rotor axis. 
         FIG.  8    is a schematic diagram of the drive unit as seen from the direction of the rotor axis. 
         FIG.  9    is an enlarged view in the vicinity of the connecting portion of an outer housing. 
         FIG.  10    is a cross-sectional view of the connecting portion. 
         FIG.  11    is a schematic view of the outer housing from the direction of the rotor axis. 
         FIG.  12    is a schematic view of the outer housing from below. 
         FIG.  13    is a first diagram explaining the cooling order of the embodiment. 
         FIG.  14    is a second diagram explaining the cooling order of the embodiment. 
         FIG.  15    is a third diagram explaining the cooling order of the embodiment. 
         FIG.  16    is a fourth diagram explaining the cooling order of the embodiment. 
         FIG.  17    is a diagram showing an arrangement of fastening parts when there is an even number of fastening parts. 
         FIG.  18    is a diagram showing an arrangement of fastening parts when there is an odd number of fastening parts. 
         FIG.  19 A  is a diagram of a first example of phase difference when there is an even number of fastening parts. 
         FIG.  19 B  is a diagram showing a second example of phase difference when there is an even number of fastening parts. 
         FIG.  19 C  is a diagram showing a third example of phase difference when there is an even number of fastening parts. 
         FIG.  19 D  is a diagram showing a fourth example of phase difference when there is an even number of fastening parts. 
         FIG.  19 E  is a diagram showing a fifth example of phase difference when there is an even number of fastening parts. 
         FIG.  19 F  is a diagram showing a sixth example of phase difference when there is an even number of fastening parts. 
         FIG.  20 A  is a diagram showing a first example of phase difference when there is an odd number of fastening parts. 
         FIG.  20 B  is a diagram showing a second example of phase difference when there is an odd number of fastening parts. 
         FIG.  20 C  is a diagram showing a third example of phase difference when there is an odd number of fastening parts. 
         FIG.  20 D  is a diagram showing a fourth example of phase difference when there is an odd number of fastening parts. 
         FIG.  20 E  is a diagram showing a fifth example of phase difference when there is an odd number of fastening parts. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to the drawings. 
     Outline of Drive Unit 
       FIG.  1    is an external view of a drive unit  100  according to an embodiment. The drive unit  100  is used to drive a series hybrid vehicle and includes a drive motor  15 , a generator motor  17 , an inverter  13 , a speed reduction mechanism  18 , and a speed increase mechanism  19 , which will be described further below. Further, the drive motor  15  and the generator motor  17  are water-cooled, and the drive unit  100  is equipped with a water-cooled cooling system. The cooling system consists of a radiator  1 , a water pump  2 , external cooling passages  3 - 6 , and internal cooling passages. The internal cooling passages consist of an inverter cooling passage  42  formed integrally with the inverter  13 , a drive motor cooling passage (not shown) that cools the drive motor  15 , and a generator motor cooling passage (not shown) that cools the generator motor  17 , which are interconnected in the housing of the drive unit  100 . These internal cooling passages will be described in detail below. 
     Coolant cooled by the radiator  1  flows into the inverter cooling passage  42  via the first external cooling passage  3 , the water pump  2 , and the second external cooling passage  4 , passes through the drive motor cooling passage and the generator motor cooling passage, and returns to the radiator  1  via the third external cooling passage  6 . In this manner, in the drive unit  100  of this embodiment, the inverter  13 , the drive motor  15 , and the generator motor  17  are cooled using the internal cooling passages, so that the external cooling passages only require two paths, the path from the radiator  1  to the drive unit  100  (first external cooling passage  3  and second external cooling passage  4 ), and the path from the drive unit  100  to the radiator  1  (the third external cooling passage  6 ). 
       FIG.  2    shows a drive unit  101  as a comparative example. The drive unit  101  of the comparative example is the same as the drive unit  100  in that the inverter  13 , the drive motor  15 , and the generator motor  17  are integrated, but the cooling passages for cooling these elements are connected via external cooling passages. That is, in addition to the first external cooling passage  3 , the second external cooling passage  4 , and the third external cooling passage  6  of  FIG.  1   , an external cooling passage  7  that connects a cooling passage for the inverter and a cooling passage for the drive motor, as well as an external cooling passage  8  that connects the cooling passage for the drive motor and a cooling passage for the generator motor are required. 
     As described above, the drive unit  100  and the cooling system of this embodiment have fewer external cooling passages than the drive unit  101  and the cooling system of the comparative example. That is, the drive unit  100  and the cooling system of this embodiment have a more compact configuration than the configuration of the comparative example and have greater flexibility of design of the layout when mounted in a vehicle. 
       FIG.  3    is an exploded view of the drive unit  100  according to this embodiment. 
     The housing of the drive unit  100  comprises an outer housing  10 , a gear cover  11  that is attached to one end portion of the outer housing  10 , and a rear cover  12  that is attached to the other end portion of the outer housing  10 . 
     The outer housing  10  has the form of two parallel cylindrical sections. The drive motor  15  and a first inner housing  14  in which the drive motor is accommodated are housed in one cylindrical portion, and the generator motor  17  and a second inner housing  16  in which the generator motor is accommodated are housed in the other cylindrical portion. The drive motor  15  consists of a stator  15 B that is fixed inside the inner housing  14  and a rotor  15 A that is fixed to the rear cover  12 . Similarly, the generator motor  17  also consists of a stator  17 B that is fixed inside the inner housing  16  and a rotor  17 A that is fixed to the rear cover  12 . 
     Further, the inverter  13  is mounted on the upper portion of the outer housing  10 . The upper portion here is the part above the plane that includes the axis of rotation of the drive motor  15  and the axis of rotation of the generator motor  17 . Although the drive unit  100  may be mounted in the vehicle in a state in which the plane that includes the axes of rotation of the two motors  15 ,  17  is inclined with respect to the horizontal direction, as shown in  FIG.  4   , in this embodiment, the part above the plane in the perpendicular direction is referred to as the upper side, and the part below the plane is referred to as the lower side. 
     The gear cover  11  houses the speed decrease mechanism  18  connected to the drive motor  15 , the speed increase mechanism  19  connected to the generator motor  17 , and a mechanical pump  20 . 
     A sensor  21  that detects the rotational speed of the drive motor  15 , a sensor  22  that detects the rotational speed of the generator motor  17 , and a sensor cover  23  that covers these sensors are attached to the rear cover  12 . 
     Further, a shielding plate  24 , described further below, is attached to the outer housing  10 . 
     Inner Housing 
     The inner housings  14 ,  16  will now be described. The first inner housing  14  and the second inner housing  16  have the same structure and are thus referred to as inner housing IHSG when there is no need to distinguish between them. 
       FIG.  5    is an external view of the inner housing IHSG. 
     The stators of the motors  15 ,  17  are fixed to inner circumference  30  of the inner housing IHSG. A helical groove  32  is formed from one end to the other of outer circumferential surface  31  of the inner housing IHSG. When the inner housing IHSG is housed in the outer housing  10 , the upper opening of the groove  32  is closed by the inner circumferential surface of the outer housing  10 , thereby forming a helical cooling passage (hereinafter referred to as the helical cooling passage  32 ). However, the upper openings at both ends of the helical cooling passage  32  are not closed, even when housed in the outer housing  10 , and function as an inlet for introducing coolant into, or an outlet for discharging coolant from, the helical cooling passage  32 . In this embodiment, the end portion on the opposite side of a flange  33  of the helical cooling passage  32  is referred to as a first opening  35 , and the end portion on the flange side is referred to as a second opening  36 . The reason for providing the helical cooling passage  32  from one end of the inner housing IHSG to the other is to cover the cooling passage  32  from one axial end to the other of the outer periphery of each of the motors  15 ,  17  in contact with the inner circumference  30  of the inner housing IHSG, in order to further enhance the cooling effect. 
     The helical cooling passage  32  is formed such that the first opening  35  and the second opening  36  are positioned to form a prescribed angle with respect to the central axis when seen from the direction of the rotor axis, as shown in  FIG.  7   , described further below. As described above, the helical cooling passage  32  is provided from one end of the inner housing IHSG to the other from the standpoint of the cooling effect, so that if the position of the first opening  35  is set, the position of the second opening  36  will also be set. That is, it is not possible to set the position of the first opening  35  independently of the position of the second opening  36 . 
     Further, one end of the inner housing IHSG has a flange  33  with a plurality of fastening parts  34  for securing the inner housing to the rear cover  12  using bolts or the like. The rear cover  12  is fixed to the outer housing  10 , resulting in the inner housing IHSG being fixed to the outer housing  10  via the rear cover  12 . The inner housing IHSG may be directly fixed to the outer housing  10 . 
     The state in which the first inner housing  14  and the second inner housing  16  are housed in the outer housing  10  will now be described.  FIG.  6    is a top view of the first inner housing  14  and the second inner housing  16  in the housed state.  FIG.  7    is a view of the first inner housing  14  and the second inner housing  16  of  FIG.  6    as seen from the flange  33  side. 
     The first inner housing  14  and the second inner housing  16  are aligned so that their respective central axes are parallel and their respective flanges  33  are adjacent. Further, the first inner housing  14  and the second inner housing  16  are housed in the outer housing  10  so that their respective helical cooling passages  32  are in different phases. Here, phase means the mounting angle with respect to the outer housing  10 . That is, for example, as shown in  FIG.  7   , the straight line connecting the first opening  35  and the second opening  36  of the first inner housing  14  and the straight line connecting the first opening  35  and the second opening  36  of the second inner housing  16  are at different angles to the vertical direction of the outer housing  10  (the direction of the arrow in the figure). 
     In this embodiment, as shown in  FIG.  6   , the inner housings IHSG are housed in the outer housing  10  with a phase in which the first openings  35  of the adjacent inner housings IHSG are close to each other, and the second openings  36  of the adjacent inner housings IHSG are far from each other. This makes the distance L 1  from the first opening  35  of the first inner housing  14  to the first opening  35  of the second inner housing  16  shorter than the distance L 2  from the second opening  36  of the first inner housing  14  to the second opening  36  of the second inner housing  16 . 
     Cooling Passages 
     The cooling passages in the drive unit  100  will be described with reference to  FIGS.  8  to  12   . 
       FIG.  8    is a schematic diagram of the drive unit  100  as seen from the same direction as in  FIG.  7   . 
     The inverter  13  has a first power module  40  and a second power module  41  that constitute an inverter circuit and the inverter cooling passage  42  that cools the power modules. The inverter cooling passage  42  is configured such that coolant introduced from the water pump  2  cools the first power module  40  and then cools the second power module  41 . 
     A liquid seal  47  for ensuring airtightness is interposed between the inverter  13  and the outer housing  10 . An O-ring  48  for ensuring watertightness, which will be described further below, is disposed at a connecting portion between the inverter cooling passage  42  and an outer housing introduction passage  43 , also described further below. 
     The inverter cooling passage  42  after passing through the second power module  41  is connected to the outer housing introduction passage  43  provided in the outer housing  10 . The outer housing introduction passage  43  is connected to the second opening  36  of the first inner housing  14 . That is, the second opening  36  of the first inner housing  14  functions as a coolant inlet. On the other hand, the first opening  35  of the first inner housing  14  functions as a coolant outlet. 
     The first opening  35  of the first inner housing  14  is connected to the first vertical passage  45 A of a connecting channel or connecting passage  45 , which includes the first vertical passage  45 A, a horizontal passage  45 B, a second vertical passage  45 C, and a cover  46 . The connecting passage  45  will be described further below. 
     The second vertical passage  45 C of the connecting passage  45  is connected to the first opening  35  of the second inner housing  16 . That is, the first opening  35  of the second inner housing  16  functions as a coolant inlet. On the other hand, the second opening  36  of the second inner housing  16  functions as a coolant outlet. An outer housing discharge passage  44  is connected to the second opening  36  of the second inner housing  16 . 
     A connecting portion  49  between the inverter cooling passage  42  and the outer housing introduction passage  43  will now be described with reference to  FIGS.  9  and  10   . 
       FIG.  9    is an enlarged view in the vicinity of the connecting portion  49  of the outer housing  10 .  FIG.  10    shows a cross section of the connecting portion  49 . 
     An inverter circuit placement area  52  is surrounded by a liquid seal placement surface  51 . The outer housing introduction passage  43  is located on the outside of the inverter circuit placement area  52 . 
     A trap groove  50  is provided between the liquid seal placement surface  51  and the connecting portion  49 . As shown in  FIG.  10   , a groove may be formed in the inverter at a location opposite the trap groove  50 . By providing the trap groove  50 , even if the liquid seal  47  that is crushed as a result of fastening the inverter  13  to the outer housing  10  protrudes from the liquid seal placement surface  51 , the protruding liquid seal  47  is accommodated in the trap groove  50 . Thus, the watertightness realized by the  0 -ring  48  of the connecting portion  49  can be prevented from becoming impaired due to the protruding liquid seal  47 . 
     The connecting passage  45  will now be described with reference to  FIGS.  11  and  12   . 
       FIG.  11    schematically shows a cross section of the outer housing  10 , in which is housed the first inner housing  14 , the drive motor  15 , the second inner housing  16 , and the generator motor  17 , as seen from the direction of the rotor axis of the motors  15 ,  17 .  FIG.  12    shows the outer housing  10  as seen from below. 
     As described above, the outer housing  10  has the form of connected cylinders that house the drive motor  15  and the generator motor  17 . A plurality of ribs  53  are formed in the valley sandwiched between the two cylindrical portions at prescribed intervals in the axial direction, as shown in  FIG.  12   . As shown in  FIG.  11   , the ribs  53  may be provided not only on the lower surface of the outer housing  10 , but also on the upper surface. 
     One of the plurality of ribs  53  is provided such that the position thereof in the direction of the rotor axis is aligned with the first opening  35  of the first inner housing  14  and the first opening  35  of the second inner housing  16 . The connecting passage  45 , described above, is formed on this rib  53 . 
     The first vertical passage  45 A penetrates from a lower end surface of the rib  53  to the interior of the outer housing  10 . The end portion of the first vertical passage  45 A on the inner side of the outer housing  10  opens opposite to the first opening  35  of the first inner housing  14 . 
     The second vertical passage  45 C penetrates from the lower end surface of the rib  53  to the interior of the outer housing  10 . The end portion of the second vertical passage  45 C on the inner side of the outer housing  10  opens opposite to the first opening  35  of the second inner housing  16 . 
     The horizontal passage  45 B is a groove provided in the lower end surface of the rib  53 , connecting the opening of the first vertical passage  45 A and the opening of the second vertical passage  45 C. When this groove is closed by the cover  46  from below, the first vertical passage  45 A, the horizontal passage  45 B, and the second vertical passage  45 C form the connecting passage  45  that connects the first opening  35  of the first inner housing  14  and the first opening  35  of the second inner housing  16 . 
     Coolant Flow 
     The flow of the coolant through the drive unit  100  according to this embodiment will be described with reference to  FIGS.  13  to  16   . 
       FIG.  13    is a top view of the drive unit  100 .  FIG.  14    is a view of the drive unit  100  from the side on which the drive motor  15  is housed, that is, the drive unit  100  is viewed from above the plane of the paper of  FIG.  13   .  FIG.  15    is an enlarged view in the vicinity of the connecting passage  45  as seen from the rear cover  12  side.  FIG.  16    is a view of the drive unit  100  as seen from the generator motor  17  side. 
     The coolant cooled by the radiator  1  flows into the inverter cooling passage  42 , as shown in  FIG.  13   . 
     The coolant that has cooled the first power module  40  and the second power module  41  while passing through the inverter cooling passage  42  flows into the helical cooling passage  32  of the first inner housing  14  via the connecting portion  49  and the outer housing introduction passage  43 , as shown in  FIG.  14   , and cools the drive motor  15 . 
     The coolant that has cooled the drive motor  15  flows into the helical cooling passage  32  of the second inner housing  16  via the connecting passage  45 , as shown in  FIG.  15   , and cools the generator motor  17 , as shown in  FIG.  16   . 
     As described above, the coolant cools the inverter  13 , the drive motor  15 , and the generator motor  17 , in that order. That is, in this embodiment, when viewed in the order of the coolant flow, the drive motor  15  is the upstream side motor and the generator motor  17  is the downstream side motor. 
     Regarding Phase 
     The phase setting method will be described with reference to  FIGS.  17  to  20   . 
       FIG.  17    shows the case of an equally spaced arrangement of six fastening parts  34  in the circumferential direction, in the same manner as shown in  FIG.  8   , etc. 
     To make the drive unit  100  compact, the distance L 3  between the axes of the first inner housing  14  and the second inner housing  16  must be reduced. In other words, the outer peripheries of the first inner housing  14  and the second inner housing  16  must be brought close together. To do so, as shown in  FIG.  17   , two of the fastening parts  34  on the second inner housing  16  side, from among the six fastening parts  34  of the second inner housing  16 , and two of the fastening parts  34  on the first inner housing  14  side, from among the six fastening parts  34  of the first inner housing  14 , must be respectively in phases opposite each other. The phase difference patterns that satisfy this condition are shown in  FIGS.  19 A to  19 F . 
       FIG.  19 A to  19 F  are diagrams in which the first inner housing  14  and the second inner housing  16  are concentrically superposed, and the phase difference is represented by reference lines D 1 , D 2  that connect the centers and the respective reference fastening parts  34 .  FIG.  19 A  shows the state of  FIG.  17   , that is, the case in which the phase difference θ is zero. Here, the phase difference θ is a multiple of the value obtained by dividing 360 degrees by the number of fastening parts  34  (six), i.e., a multiple of 60 degrees. In this manner, the arrangement of the fastening parts  34  will be the same as that shown in  FIG.  17    for any phase difference θ. 
       FIGS.  19 B to  19 F  show cases in which the phase difference θ is 60 degrees, 120 degrees, 180 degrees, 240 degrees, 300 degrees, and 360 degrees, respectively. That is, when there are six fastening parts  34 , there are six possible patterns of the phase difference θ, 60 degrees×0, 60 degrees×1, 60 degrees×2, . . . 60 degrees×6. If there are an even number of fastening parts  34 , the same concept as above can be applied. Specifically, where a is the number of fastening parts  34  and 360/a=b, the possible phase differences θ are 0×b, 1&gt;b, 2×b, . . . , a×b. 
     If there are an odd number of the fastening parts  34 , on the other hand, the outer peripheries of the first inner housing  14  and the second inner housing  16  must still be brought close together in order to make the drive unit  100  have a compact configuration, in the same manner as when there are an even number of the fastening parts  34 . For example, if there are five fastening parts  34 , the arrangement would be as shown in  FIG.  18   . In  FIG.  18   , there is a phase difference between the first inner housing  14  and the second inner housing  16 . That is, the reference line D 3  of the first inner housing  14  and the reference line D 4  of the second inner housing  16  are not parallel, and the phase difference θ is 360 degrees÷5÷2=36 degrees. The possible phase differences θ when the number of the fastening parts  34  is five are as shown in  FIGS.  20 A to  20 E .  FIGS.  20 A to  20 E  show the phase differences θ, in the same manner as in  FIGS.  19 A to  19 F , and  FIG.  20 A  shows the state of  FIG.  18   . The phase differences θ shown in  FIGS.  20 A to  20 E  are 36 degrees, 108 degrees, 180 degrees, 252 degrees, and 324 degrees, respectively. That is, the phase differences θ for an odd number of fastening parts  34  where the number of the fastening parts  34  is c and 360/c=d are 0×d+d/2, 1×d+d/2, 2×d+d/2, . . . c×d+d/2. 
     One phase difference θ out of the possible phase differences θ described above will be adopted in accordance with the drive unit  100  to be used. 
     Effects 
     The effects of the configuration of this embodiment will now be described. 
     The drive unit  100  according to this embodiment is a drive unit of a series hybrid vehicle and comprises the drive motor  15  (first electric motor for driving) and the generator motor  17  (second electric motor). The first cylindrical inner housing  14  provided on the outer periphery of the stator of the drive motor  15  and the second cylindrical inner housing  16  provided on the outer periphery of the stator of the generator motor are each provided with the helical cooling passage  32  on the respective outer periphery, formed so as to surround each stator in helical fashion. The drive motor  15  and the generator motor  17  are housed in the outer housing  10  such that the rotor axes are parallel. The helical cooling passage  32  of the drive motor  15  and the helical cooling passage  32  of the generator motor  17  are connected in series via the connecting passage  45 , and the first opening  35  (coolant outlet) of the helical cooling passage  32  on the upstream side to which one end of the connecting passage  45  is connected and the first opening  35  (coolant inlet) of the helical cooling passage  32  on the downstream side to which the other end of the connecting passage  45  is connected are arranged at the end portions on the same side in the direction of the rotor axis. 
     That is, in the helical cooling passage  32  on the upstream side, the first opening  35  becomes the coolant outlet, and in the cooling passage  32  on the downstream side, the first opening  35  becomes the coolant inlet. As a result, in any of the helical cooling passages  32 , the length of the channel of the connecting passage  45  can be suppressed, compared with the case in which the first opening  35  is set as the coolant outlet and the second opening  36  is set as the coolant inlet. As a result, the drive unit  100  can be made compact. 
     In this embodiment, the first inner housing  14  and the second inner housing  16  are housed in the outer housing  10  so that the respective helical cooling passages  32  have different phases. In other words, the same parts can be used for the inner housing  14  that houses the drive motor  15  and the inner housing  16  that houses the generator motor  17 . As a result, the parts count is reduced compared with the case in which two types of inner housings IHSGs are used, so that the manufacturing cost of the drive unit  100  can be suppressed. Further, although a case in which the diameter of the drive motor  15  and the diameter of the generator motor  17  are the same was described in the above embodiment, no limitation is imposed thereby; for example, if the motors to be used are changed and the diameter of the drive motor  15  and the diameter of the generator motor  17  are different, two types of inner housings IHSG could be used. However, even in this case, if the pitch of the helix of the helical cooling passage  32  on the upstream side matches the pitch of the helix of the helical cooling passage  32  on the downstream side, the flow path need not be redesigned. Here, the pitch of the helix is the distance between the valleys of the inner housing IHSG in the axial direction. 
     In this embodiment, the distance between the first opening  35  (coolant outlet) of the helical cooling passage  32  on the upstream side and the first opening  35  (coolant inlet) of the helical cooling passage  32  on the downstream side is shorter than the distance between the second opening  36  (coolant outlet) of the helical cooling passage  32  on the downstream side and the second opening  36  (coolant inlet) of the helical cooling passage  32  on the upstream side. 
     As a result, the length of the channel of the connecting passage  45  can be further suppressed. 
     In this embodiment, the inverter  13  is disposed on the upper portion of the outer housing  10 , the first opening  35  (coolant outlet) of the helical cooling passage  32  on the upstream side is disposed below the rotor axis of the drive motor  15  (the electric motor on the upstream side), and the first opening  35  (coolant inlet) of the helical cooling passage  32  on the downstream side is disposed below the rotor axis of the generator motor  17  (the electric motor on the downstream side). That is, the inverter  13  is disposed in a position higher than the connecting portion between the connecting passage  45  and the two helical cooling passages  32 . Thus, even in the event of a leak due to a problem in the connecting portion, leakage into the inverter circuit can be prevented. 
     In this embodiment, the inverter  13  is disposed on the upper portion of the outer housing  10 , and, as shown in  FIGS.  9  and  10   , the outlet of the inverter cooling passage  42  is provided on the outside of the airtight seal of the inverter  13 . The outlet of the inverter cooling passage  42  and the coolant inlet of the helical cooling passage  32  on the upstream side are connected via the outer housing introduction passage  43 . Thus, even in the event of a leak due to a problem in the connecting portion between the inverter cooling passage  42  and the outer housing introduction passage  43 , leakage into the inverter circuit can be prevented. 
     In this embodiment, the first opening  35  (the coolant outlet) of the helical cooling passage  32  on the upstream side is disposed on the side away from the generator motor  17  (the electric motor on the downstream side) with respect to the rotor axis of the drive motor  15  (the electric motor on the upstream side) as seen from the axial direction of the rotor axis. In other words, the coolant inlet of the helical cooling passage  32  on the upstream side is disposed on the side close to the outer edge of the outer housing  10  on the first inner housing  14  side. The coolant outlet of the helical cooling passage  32  on the upstream side is thus positioned near the helical cooling passage  32  on the downstream side, as shown in  FIG.  8   , and it is possible to suppress the length of the channel of the connecting passage  45 . 
     In this embodiment, the outer housing  10  has a form in which a first cylindrical portion  10 A housing the drive motor  15  (the first electric motor) and a second cylindrical portion  10 B housing the generator motor  17  (the second electric motor) are adjacent, and has at least one rib  53  that connects the first cylindrical portion  10 A and the second cylindrical portion  10 B in the lower side valley between the first cylindrical portion  10 A and the second cylindrical portion  10 B. One of the ribs  53  has the connecting passage  45  (the channel) composed of the first vertical passage  45 A (the first through-hole) that runs from the lower end surface of the rib  53  to the interior of the first cylindrical portion  10 A, the second vertical passage  45 C (the second through-hole) that runs from the lower end surface of the rib  53  to the interior of the second cylindrical portion  10 B, the horizontal passage (the connection groove)  45 B that is provided on the lower end surface of the rib  53  and that connects the first vertical passage  45 A and the second vertical passage  45 C, and the cover  46  (the lid member) that closes the horizontal passage  45 B. 
     This allows the helical cooling passage  32  on the upstream side to be connected to the helical cooling passage  32  on the downstream side with a simple configuration while ensuring the rigidity of the outer housing  10 . 
     In this embodiment, the first inner housing  14  and the second inner housing  16  are fixed to the outer housing  10  via the plurality of fastening parts  34  provided on the respective outer peripheral portions at equal intervals in the circumferential direction. If there are an even number of fastening parts  34 , the phase difference between the first inner housing  14  and the second inner housing  16  is a multiple of the angle obtained by dividing 360 degrees by the number of the fastening parts  34  of each inner housing IHSG, and if there are an odd number of fastening parts  34 , the phase difference is a multiple of the angle obtained by dividing 360 degrees by the number of the fastening parts  34  of each inner housing IHSG plus half of said angle. 
     More specifically, the angle for which the length of the channel of the connecting passage  45  is shorter is selected from the angles described above, in accordance with the positions of the first opening  35  and the second opening  36 . 
     In this embodiment, the cover  46  is a plate-shaped member that only has the function of closing the horizontal passage  45 B, but in the case that the drive motor  15 , etc., are oil/water-cooled types, which use both oil and a coolant, the cover  46  may have the function of an oil cooler. For example, an oil passage may be formed inside the cover  46 , and the configuration is such that heat is exchanged between the oil and the coolant that flows in the horizontal passage  45 B. 
     An embodiment of the present invention was described above, but the above-described embodiment illustrates only some of the application examples of the present invention, and is not intended to limit the technical scope of the present invention to the specific configurations of the above-described embodiment.