Patent Publication Number: US-2023146341-A1

Title: Lubrication structure for vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-184404 filed on Nov. 11, 2021, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a lubrication structure for a vehicle, and in particular to a lubrication structure for supplying lubricating oil to a rotary machine and a bearing member through separate pipes. 
     2. Description of Related Art 
     A lubrication structure for a vehicle is known, which includes a first lubrication pipe through which lubricating oil is supplied to a rotary machine disposed in a case, a second lubrication pipe through which lubricating oil is supplied to a bearing member disposed in the case, and an oil pump that supplies lubricating oil to the first lubrication pipe and the second lubrication pipe. For example, Japanese Unexamined Patent Application Publication No. 2019-162927 (JP 2019-162927 A) proposes a lubrication structure related to (a) a hybrid electric vehicle that includes an engine [engine 10], a power transfer device that transfers a drive force transferred from the engine to drive wheels via an output portion [differential 24 etc.], and a travel rotary machine [second electric motor MG2] coupled to the output portion, the lubrication structure including (b) a case [case 60] that houses the power transfer device and the travel rotary machine therein, (c) an I/P pump [input shaft MOP 51] mechanically rotationally driven by the engine to discharge lubricating oil, (d) an O/P pump [output shaft MOP 52] coupled to the output portion and mechanically rotationally driven to discharge lubricating oil, (e) an I/P oil path [first oil path 71] connected to the discharge side of the I/P pump to supply lubricating oil to the travel rotary machine, and (f) an O/P oil path [second oil path 72] connected to the discharge side of the O/P pump to supply lubricating oil to the power transfer device [speed reduction unit 56 etc.]. The I/P oil path is constituted using a first lubrication pipe as necessary. The O/P oil path is constituted using a second lubrication pipe as necessary. Bearing members at various portions are supplied with lubricating oil mainly from the O/P oil path. Meanwhile, Japanese Unexamined Patent Application Publication No. 2014-119085 (JP 2014-119085 A) describes a lubrication structure that supplies lubricating oil splashed up by a final gear to portions to be lubricated such as a planetary gear device via an oil guide member and an oil gutter. 
     The term “lubrication” as used herein is used not only when it is intended to reduce friction or wear but also when lubricating oil is supplied to a rotary machine etc. to cool the rotary machine etc. 
     SUMMARY 
     Even with such a lubrication structure for a vehicle, however, the amount of lubricating oil to be supplied to bearing members may be insufficient to cause a seizure when the viscosity of the lubricating oil is high in environments at extremely low temperatures. In particular with the lubrication structure according to JP 2014-119085 A in a form of splash-up lubrication, and also with the lubrication structure according to JP 2019-162927 A in a form of forced lubrication in which lubricating oil is supplied using an oil pump, the amount of oil to be supplied to bearing members etc. may be insufficient at extremely low temperatures, since the lubrication structures are designed such that an excessive amount of lubricating oil is not supplied from the viewpoint of the power transfer efficiency. 
     The present disclosure allows lubricating oil to be stably supplied to a bearing member even in environments at extremely low temperatures with a simple configuration when lubricating oil is supplied to a rotary machine and the bearing member from separate pipes. 
     An aspect of the present disclosure provides a lubrication structure for a vehicle including: a first lubrication pipe through which lubricating oil is supplied to a rotary machine disposed in a case; a second lubrication pipe through which the lubricating oil is supplied to a bearing member disposed in the case; and an oil pump that supplies the lubricating oil to the first lubrication pipe and the second lubrication pipe. The lubrication structure includes (a) a first oil hole provided in the case to supply the lubricating oil to the rotary machine, the first lubrication pipe being connected to the first oil hole, and (b) a second oil hole provided in the case to supply the lubricating oil to the bearing member, the lubricating oil flowing into the second oil hole from the second lubrication pipe, and (c) a connection portion between the first lubrication pipe and the first oil hole is located at a position above an opening portion of the second oil hole such that at least a part of the lubricating oil that has flowed out from the connection portion flows into the second oil hole. 
     In such a lubrication structure for a vehicle, the connection portion between the first lubrication pipe through which lubricating oil is supplied to the rotary machine and the first oil hole is located at a position above the opening portion of the second oil hole into which lubricating oil flows from the second lubrication pipe through which lubricating oil is supplied to the bearing member such that at least a part of the lubricating oil that has flowed out from the connection portion flows into the second oil hole. Therefore, it is possible to suppress a shortage in the amount of lubricating oil to be supplied to the bearing member at extremely low temperatures at which the viscosity of the lubricating oil is high. It is only necessary to allow lubricating oil to flow out from the connection portion between the first lubrication pipe and the first oil hole, and to provide the opening portion of the first oil hole at a position above the opening portion of the second oil hole. Such a structure can be implemented easily without requiring a significant design change, and can be constituted inexpensively compared to a case in which the oil pump that supplies lubricating oil to the second lubrication pipe is increased in size such that a sufficient amount of lubricating oil is supplied to the bearing member even at extremely low temperatures. 
     In the lubrication structure according to the above aspect, the first lubrication pipe may be loosely fitted in the first oil hole with a predetermined gap without interposing a seal member such as an O-ring at the connection portion such that the lubricating oil leaks out and flows downward from the connection portion even at an extremely low temperature at which a viscosity of the lubricating oil is high. 
     It is only necessary to loosely fit the first lubrication pipe in the first oil hole with a predetermined gap without interposing a seal member such as an O-ring such that the lubricating oil leaks out and flows downward from the connection portion between the first lubrication pipe and the first oil hole. Such a structure can be implemented easily and inexpensively. 
     In the lubrication structure according to the above aspect, a V-shaped or U-shaped oil receiver that opens upward and becomes wider upward may be provided at the opening portion of the second oil hole, and the connection portion may be positioned such that at least a part of the connection portion overlaps the oil receiver in a vertical direction. 
     The V-shaped or U-shaped oil receiver is provided at the opening portion of the second oil hole, and the connection portion is positioned such that at least a part of the connection portion overlaps the oil receiver in the vertical direction. Therefore, at least a part of the lubricating oil that has flowed downward from the connection portion is received by the oil receiver and allowed to reliably flow into the second oil hole, which appropriately suppresses a shortage in the amount of lubricating oil to be supplied to the bearing member. 
     In the lubrication structure according to the above aspect, (a) the vehicle may be a hybrid electric vehicle that includes an engine, a power transfer device that transfers a drive force transferred from the engine to drive wheels via an output portion, and a travel rotary machine coupled to the output portion; (b) the power transfer device and the travel rotary machine may be housed in the case, the travel rotary machine may be the rotary machine, the bearing member may be provided to support a predetermined rotary element of any of the power transfer device and the rotary machine, and (c) the one or more oil pumps may include an I/P (an abbreviation of “IN/PUT”) pump mechanically rotationally driven by the engine to discharge the lubricating oil and an O/P (an abbreviation of “OUT/PUT”) pump coupled to the output portion and mechanically rotationally driven to discharge the lubricating oil; and (d) the lubricating oil may be supplied from the I/P pump to the first lubrication pipe and used to cool a stator of the travel rotary machine, and the lubricating oil may be supplied from the O/P pump to the second lubrication pipe and used to lubricate the bearing member. 
     When the lubrication structure is for a hybrid electric vehicle, and includes an I/P pump mechanically rotationally driven by the engine and an O/P pump coupled to the output portion and mechanically rotationally driven, the lubricating oil is supplied from the I/P pump to the first lubrication pipe, and the lubricating oil is supplied from the O/P pump to the second lubrication pipe. In this case, a part of the lubricating oil discharged from the I/P pump is caused to flow into the second oil hole and to be supplied to the bearing member, which makes it possible to suppress a shortage in the amount of lubricating oil to be supplied to the bearing member at extremely low temperatures without increasing the O/P pump in size. Additionally, the amount of lubricating oil to be supplied from the second lubrication pipe to the bearing member is decreased with the discharge amount of the O/P pump reduced at low vehicle speeds. However, a part of the lubricating oil supplied from the I/P pump to the first lubrication pipe flows out from the connection portion with the first oil hole and flows into the second oil hole, which also suppresses a shortage in the amount of lubricating oil to be supplied to the bearing member at low vehicle speeds. 
     In the lubrication structure according to the above aspect, a discharge capacity of the I/P pump may be larger than a discharge capacity of the O/P pump. The discharge capacity is the amount of lubricating oil to be discharged per rotation. 
     When the discharge capacity of the I/P pump is larger than the discharge capacity of the O/P pump, the I/P pump with a larger discharge capacity is less affected by the viscosity of the lubricating oil. Therefore, a sufficient amount of lubricating oil can be supplied to the travel rotary machine to appropriately cool the travel rotary machine even at extremely low temperatures at which the viscosity of the lubricating oil is high. In addition, a part of the lubricating oil is caused to flow into the second oil hole to be supplied to the bearing member, which appropriately provides the effect of suppressing a shortage in the amount of lubricating oil to be supplied to the bearing member without increasing the O/P pump in size. 
     In the lubrication structure according to the above aspect, the opening portion of the second oil hole may be located off a position directly below the connection portion, and an oil guide in an inclined gutter shape may be provided directly below the connection portion to guide at least a part of the lubricating oil that has flowed out from the connection portion into the second oil hole. 
    
    
     
       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 signs denote like elements, and wherein: 
         FIG.  1    is a schematic diagram illustrating a hybrid electric vehicle with a lubrication structure to which the present disclosure is applied, and is a development view in which a plurality of axes of a power transfer device is illustrated to be positioned in a common plane; 
         FIG.  2    is a block diagram illustrating a vehicle lubrication system provided in the hybrid electric vehicle in  FIG.  1    as the lubrication structure; 
         FIG.  3    is a perspective view of the power transfer device specifically illustrating the vehicle lubrication system in  FIG.  2   , in which a transaxle case is omitted; 
         FIG.  4    is a front view illustrating a state in which an I/P oil pipe and an O/P oil pipe that constitute oil paths of the vehicle lubrication system in  FIG.  2    are attached to a partition wall of the transaxle case; 
         FIG.  5    is a perspective view in which a part of the transaxle case in  FIG.  4   , that is, the upper left portion of  FIG.  4    in which the I/P oil pipe is connected to a communication oil hole, is illustrated as enlarged; 
         FIG.  6    is a sectional view of the power transfer device for a portion corresponding to the VI-VI sectional plane in  FIG.  5   , illustrating the structure of bearings for a rotor shaft and a gear shaft disposed on a third axis S 3  and the connection structure of the I/P oil pipe connected at a position above the third axis S 3 ; 
         FIG.  7    is a perspective view corresponding to  FIG.  5   , illustrating another embodiment of the present disclosure; and 
         FIG.  8    is a block diagram of a vehicle lubrication system corresponding to  FIG.  2   , illustrating still another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The present disclosure is applicable to a variety of vehicles that include a first lubrication pipe through which lubricating oil is supplied to a rotary machine, a second lubrication pipe through which lubricating oil is supplied to a bearing member, and an oil pump. The rotary machine is a motor generator that has the function of an electric motor or an electric generator, or both functions. That is, the present disclosure is applicable to lubrication structures for a variety of vehicles such as an engine driven vehicle that includes an engine (internal combustion engine) as a drive force source, a hybrid electric vehicle of a parallel kind or a series kind that includes an engine and a rotary machine, and a battery electric vehicle that travels by driving an electric motor using power from a power source such as a battery. While the first lubrication pipe through which lubricating oil is supplied to the rotary machine is configured to, for example, cool the rotary machine by supplying lubricating oil to a stator of the rotary machine, the first lubrication pipe may be a pipe for supplying lubricating oil to a rotor shaft of the rotary machine or a bearing member for the rotor shaft. The second lubrication pipe allows lubricating oil to be supplied to a portion that is different from the first lubrication pipe. When the first lubrication pipe allows lubricating oil to be supplied to the bearing member for the rotor shaft, the second lubrication pipe is configured to allow lubricating oil to be supplied to a bearing member for a rotary element that is different from the rotor shaft. The bearing member may be a sliding bearing, a thrust bearing, etc., besides a rolling bearing that supports rotation about an axial center such as a ball bearing and a roller bearing. 
     The oil pump is provided separately for each of the first lubrication pipe and the second lubrication pipe, for example. However, the oil pump may be provided in a manner that lubricating oil discharged from a single, common oil pump is divided to be supplied to the first lubrication pipe and the second lubrication pipe. The oil pump may be a mechanical oil pump mechanically rotationally driven by the engine, a predetermined rotary member in a power transfer path, etc., or may be an electric oil pump rotationally driven by a dedicated electric motor. When a plurality of oil pumps is provided as the oil pump, the respective discharge capacities of such oil pumps may be different from or equal to each other. 
     To allow lubricating oil to flow out from a connection portion between the first lubrication pipe and the first oil hole, it is only necessary to loosely fit the first lubrication pipe in an opening portion of the first oil hole without interposing a seal member such as an O-ring with a gap (play) provided between the first lubrication pipe and the first oil hole, for example. However, a cutout, a groove, a through hole, etc. may be provided at or in the vicinity of the connection portion in order to allow lubricating oil to flow out at a predetermined flow rate. The connection between the first lubrication pipe and the first oil hole is suitably made through fitting, for example, but may also be made through screwing, butt joining, etc. A V-shaped or U-shaped oil receiver that opens upward and becomes wider upward, for example, is provided at an opening portion of a second oil hole. The connection portion between the first lubrication pipe and the first oil hole is positioned such that at least a part of the connection portion overlaps the oil receiver in the vertical direction. However, the opening portion of the second oil hole may be provided at a position displaced in a horizontal direction from a position vertically below the connection portion between the first lubrication pipe and the first oil hole, and an oil guide in a gutter shape may be provided on a wall surface of a case etc. to receive lubricating oil that has flowed out and flowed downward from the connection portion and guide the lubricating oil to the opening portion of the second oil hole. 
     Embodiments of the present disclosure will be described in detail below with reference to the drawings. The drawings for the following embodiments are simplified or deformed as appropriate for illustration, and the dimensional ratios, shapes, etc. of the various portions are not necessarily accurate. 
       FIG.  1    is a schematic diagram illustrating a power transfer device  12  of a hybrid electric vehicle  10  (hereinafter simply referred to as a “vehicle  10 ”) that includes a vehicle lubrication system  120  (see  FIG.  2   ) as a lubrication structure according to an embodiment of the present disclosure, and is a development view in which a plurality of axes that constitutes the power transfer device  12  is illustrated to be positioned in a common plane. The power transfer device  12  is a transaxle of a transversely mounted kind for front-engine front-wheel-drive (FF) vehicles etc. in which a plurality of axes is disposed along the vehicle width direction, and includes a first axis S 1  to a fourth axis S 4  that are substantially parallel to the vehicle width direction, that is, substantially horizontal. An input shaft  22  coupled to an engine  16  via a damper device  18  is provided on the first axis S 1 . A single-pinion planetary gear device  24  and a first rotary machine MG 1  are disposed coaxially with the first axis S 1 . The planetary gear device  24  and the first rotary machine MG 1  function as an electric differential unit  26 . The input shaft  22  is coupled to a carrier  24   c  of the planetary gear device  24  which is a differential mechanism. A rotor shaft  28  of the first rotary machine MG 1  is coupled to a sun gear  24   s.  An engine output gear Ge is provided on a ring gear  24   r.  The sun gear  24   s  and the ring gear  24   r  are meshed with a plurality of pinions  24   p  rotatably disposed on the carrier  24   c.    
     The first rotary machine MG 1  is a motor generator that is selectively used as one of an electric motor and an electric generator, and corresponds to a rotary machine for differential control. By continuously controlling the rotational speed of the sun gear  24   s  in regeneration control etc. in which the first rotary machine MG 1  functions as an electric generator, rotation of the engine  16  is output from the engine output gear Ge with the rotational speed of the engine  16  continuously varied. That is, the electric differential unit  26  can be considered as an electric continuously variable transmission that can continuously vary a gear ratio γ (=engine rotational speed Ne/output rotational speed Nout). The engine rotational speed Ne is the rotational speed of the engine  16 . The output rotational speed Nout is the rotational speed of the engine output gear Ge. Consequently, the electric differential unit  26  can cause the engine  16  to operate at a certain optimal fuel efficiency operating point, that is, an engine rotational speed Ne and engine torque Te, at which the fuel efficiency of the engine  16  is at its best, for example, irrespective of variations in the output rotational speed Nout corresponding to a vehicle speed V. When torque of the first rotary machine MG 1  is brought to zero and the sun gear  24   s  is caused to run idle, the output from the engine  16  is blocked, and rotation of the engine  16  in an accompanying manner during motor travel, coasting, etc is restrained. The engine  16  is an internal combustion engine such as a gasoline engine or a diesel engine that generates power by combusting fuel, and is used as a drive force source for travel. The input shaft  22  is inserted through the center of the shaft of the first rotary machine MG 1  to be coupled to an I/P pump  56 . The I/P pump  56  is mechanically rotationally driven by the engine  16 . The I/P pump  56  is a mechanical oil pump mechanically rotationally driven by the engine  16 . 
     A counter shaft  36  on which a large speed reduction gear Gr 1  and a small speed reduction gear Gr 2  are provided is rotatably disposed on the second axis S 2 . The large speed reduction gear Gr 1  is meshed with the engine output gear Ge. The large speed reduction gear Gr 1  is also meshed with a motor output gear Gm disposed on the third axis S 3 . The motor output gear Gm is provided on a gear shaft  42 . The gear shaft  42  is coupled to a rotor shaft  44  of the second rotary machine MG 2  that is disposed coaxially with the third axis S 3  via a spline fitting portion  46  so as to be able to transfer power to rotor shaft  44 . The second rotary machine MG 2  is a motor generator that is selectively used as one of an electric motor and an electric generator, and is used as a drive force source for traveling when the second rotary machine MG 2  is subjected to power running control so as to function as an electric motor. The second rotary machine MG 2  corresponds to a travel rotary machine. The vehicle  10  is a hybrid electric vehicle of a multi-axis parallel kind in which the second rotary machine MG 2  is disposed on the third axis S 3  that is different from the first axis S 1  on which the engine  16  and the electric differential unit  26  are disposed. 
     The small speed reduction gear Gr 2  is meshed with a differential ring gear Gd of a differential device  48  disposed on the fourth axis S 4 . A drive force from the engine  16  and the second rotary machine MG 2  is distributed to right and left drive shafts  52  via the differential device  48  to be transferred to right and left drive wheels  54 . As illustrated in  FIG.  4   , the fourth axis S 4  is located at the lowest position in the vehicle, among the first axis S 1  to the fourth axis S 4 , the second axis S 2  and the third axis S 3  are located above the fourth axis S 4 , and the first axis S 1  is located obliquely above the fourth axis S 4  on the front side in the vehicle. The third axis S 3  on which the second rotary machine MG 2  and the gear shaft  42  are disposed is located at the highest position in the vehicle, among the first axis S 1  to the fourth axis S 4 . 
     The differential ring gear Gd is also meshed with a pump drive gear Gp. The O/P pump  58  is mechanically rotationally driven in conjunction with the differential ring gear Gd, or in other words in conjunction with the drive wheels  54 . That is, the O/P pump  58  is a mechanical oil pump meshed with the differential ring gear Gd which is an output portion and rotationally driven, to discharge lubricating oil in a discharge amount corresponding to the vehicle speed V, and discharges a larger amount of lubricating oil as the vehicle speed V is raised. The O/P pump  58  may be rotationally driven with the pump drive gear Gp meshed with a different output portion such as the large speed reduction gear Gr 1  or the small speed reduction gear Gr 2  that is rotated in conjunction with the differential ring gear Gd. 
     The power transfer device  12  includes a transaxle case  60  (hereinafter simply referred to as a “case  60 ”) integrally fixed to the engine  16  and supported by a vehicle body via a bracket etc. The case  60  is constituted from three case members, namely a front case member  62 , an intermediate case member  64 , and a rear cover  66  that are integrally joined to each other by a large number of fastening bolts with butting portions such as flanges provided at axial end portions of such members butted against each other. The front case member  62  has an opening portion that opens toward the engine  16  and that is integrally fixed to the engine  16 . A first housing space  72  is formed between the engine  16  and the front case member  62  to house the damper device  18 . The intermediate case member  64  integrally includes an outer tube  74  in a tubular shape and a partition wall  76  provided to extend generally orthogonally to the first axis S 1  to the fourth axis S 4  so as to extend toward the inner peripheral side from the outer tube  74 . A second housing space  78  is formed between the front case member  62  and the partition wall  76  to house the power transfer device  12  such as the electric differential unit  26 , the counter shaft  36 , the gear shaft  42 , and the differential device  48 . The front case member  62  and the partition wall  76  include a support portion that rotatably supports the engine output gear Ge, the counter shaft  36 , the gear shaft  42 , the differential device  48 , etc. via bearing members such as bearings. A third housing space  80  is formed between the rear cover  66  and the partition wall  76  to house the first rotary machine MG 1  and the second rotary machine MG 2 . The rear cover  66  and the partition wall  76  include a support portion that rotatably supports the rotor shafts  28  and  44  via bearing members such as bearings. The first housing space  72 , the second housing space  78 , and the third housing space  80  can also be expressed as a damper chamber, a gear chamber, and a motor chamber, respectively. 
     The vehicle  10  that includes the power transfer device  12  enables a battery electric vehicle (BEV) travel mode in which the vehicle  10  travels using only the second rotary machine MG 2  as a drive force source with the engine  16  stationary, and a hybrid electric vehicle (HEV) travel mode in which the vehicle  10  travels using at least the engine  16  as a drive force source. In the HEV travel mode, the vehicle can travel using both the engine  16  and the second rotary machine MG 2  as drive force sources by controlling the second rotary machine MG 2  so as to perform power running as necessary. 
       FIG.  2    is a block diagram of the vehicle lubrication system  120  of the vehicle  10 .  FIG.  3    is a perspective view of the power transfer device  12  specifically illustrating the vehicle lubrication system  120 , in which the case  60  is omitted.  FIG.  4    is a front view illustrating a state in which an I/P oil pipe  160  and an O/P oil pipe  166  that constitute oil paths of the vehicle lubrication system  120  are attached to the case  60 , illustrating the partition wall  76  of the intermediate case member  64  as seen from the second housing space  78  side. The vehicle lubrication system  120  includes the I/P pump  56  and the O/P pump  58  as suction devices, and lubricates the rotary machines MG 1  and MG 2  and various portions of the power transfer device  12  in a distributed manner via an I/P oil path  122  indicated by the solid line and an O/P oil path  126  indicated by the long dashed short dashed line in  FIG.  2   . The I/P pump  56  and the O/P pump  58  suck lubricating oil  152  from an oil storage portion  150  (see  FIG.  4   ) provided at the bottom portion of the case  60  via strainers  130  and  132 , respectively, and output the lubricating oil  152  to the I/P oil path  122  and the O/P oil path  126 , respectively. While separate strainers  130  and  132  are provided in the present embodiment, the I/P pump  56  and the O/P pump  58  may be configured to suck the lubricating oil  152  through a common strainer. 
     The O/P pump  58  is coupled to the differential device  48  to be mechanically rotationally driven, and therefore can be rotationally driven to suck the lubricating oil  152  in an amount that matches the vehicle speed V and supply the lubricating oil  152  to the various portions even in the BEV travel mode in which rotation of the engine  16  is stopped. The engine  16  that rotationally drives the I/P pump  56  can drive the I/P pump  56  even when the vehicle is stationary, and therefore the I/P pump  56  can suction the lubricating oil  152  in an amount that does not depend on the vehicle speed V, including when the vehicle is stationary, and supply the lubricating oil  152  to portions to be lubricated. In the BEV travel mode, however, operation of the I/P pump  56  is also stopped as rotation of the engine  16  is stopped. While the lubricating oil  152  discharged from the I/P pump  56  is mainly used to cool the rotary machines MG 1  and MG 2 , the lubricating oil  152  discharged from the O/P pump  58  is used to lubricate gear meshing portions and bearing members at various portions of the power transfer device  12 . In the present embodiment, a large pump with a larger discharge capacity than that of the O/P pump  58  is used as the I/P pump  56  such that a stable performance to cool the rotary machines MG 1  and MG 2  can be obtained. 
     The I/P oil path  122  is connected to the discharge side of the I/P pump  56  to supply the lubricating oil  152  to the rotary machines MG 1  and MG 2 . In  FIG.  2    and  FIG.  8    that illustrates another embodiment, the downward arrows pointing to the rotary machines MG 1  and MG 2  mean that the lubricating oil  152  flows downward from above the rotary machines MG 1  and MG 2  to cool the stators etc. Meanwhile, the upward arrows pointing to the rotary machines MG 1  and MG 2  mean that the lubricating oil  152  is supplied from the center side of the rotary machines MG 1  and MG 2  to cool and lubricate the rotors, the bearings, etc. The lubricating oil  152  is discharged from oil holes provided at the centers of the shaft of the input shaft  22 , the rotor shafts  28  and  44 , etc. A relief valve (escape valve)  134  is coupled to the I/P oil path  122  at a relief position  122   r  that is an intermediate position before reaching the rotary machines MG 1  and MG 2 , which suppresses the hydraulic pressure in the I/P oil path  122  becoming excessively high. An oil cooler  138  is provided on the rotary machines MG 1  and MG 2  side with respect to the relief position  122   r  at which the relief valve  134  is coupled. The lubricating oil  152  cooled by the oil cooler  138  is supplied to the rotary machines MG 1  and MG 2 . The oil cooler  138  is a water-cooled cooler that cools the lubricating oil  152  through water cooling in the present embodiment, and is disposed outside the case  60  to cool the lubricating oil  152  through heat exchange with a refrigerant in a refrigerant circulation circuit (not illustrated). The refrigerant circulation circuit circulates a refrigerant such as a coolant, and includes a radiator that cools the refrigerant using outside air, a refrigerant pump, etc. 
     The I/P oil path  122  supplies the lubricating oil  152  to predetermined portions to be lubricated through an oil hole provided in a side wall etc. of the case  60 , a pipe that is separate from the case  60 , etc. In the present embodiment, an I/P oil pipe  160  disposed in the second housing space  78  and an MG 1  oil pipe  162  and an MG 2  oil pipe  164  disposed in the third housing space  80  are provided as the pipe that is separate from the case  60 . The oil pipes  160 ,  162 , and  164  are each a resin pipe. The I/P oil pipe  160  is disposed along the partition wall  76  of the intermediate case member  64 , and fixed to the partition wall  76  at a plurality of locations. The I/P oil pipe  160  includes three connection parts  160   a  to  160   c.  The lubricating oil  152  is supplied from the oil cooler  138  to the I/P oil pipe  160  via the connection part  160   a.  The connection parts  160   b  and  160   c  are coupled to communication oil holes  76   a  and  76   b  (see  FIG.  2   ), respectively, provided in the partition wall  76 . The lubricating oil  152  is supplied to the MG 1  oil pipe  162  and the MG 2  oil pipe  164  in the third housing space  80  via the communication oil holes  76   a  and  76   b , respectively. The MG 1  oil pipe  162  and the MG 2  oil pipe  164  are each a straight pipe disposed above the first rotary machine MG 1  and the second rotary machine MG 2 , respectively, generally in parallel with the axes S 1  and S 3  thereof. The lubricating oil  152  is supplied to the MG 1  oil pipe  162  and the MG 2  oil pipe  164  with first end portions thereof in the longitudinal direction connected to the communication oil holes  76   a  and  76   b , respectively, in the partition wall  76 . The MG 1  oil pipe  162  and the MG 2  oil pipe  164  are provided with discharge holes directed downward at a plurality of locations separated from each other in the longitudinal direction. The lubricating oil  152  supplied from the I/P oil pipe  160  is discharged downward from the discharge holes to be sprayed to cool the outer peripheral surfaces of the stators of the first rotary machine MG 1  and the second rotary machine MG 2 . 
     The I/P oil path  122  includes a branch oil path  124  branched at a branch point  122   p  between the relief position  122   r  and the I/P pump  56 . The lubricating oil  152  is supplied to the first rotary machine MG 1  and the planetary gear device  24  as the electric differential unit  26  via the branch oil path  124 . The branch oil path  124  is provided with an orifice  140  that restricts the supply amount of the lubricating oil  152  that flows into the branch oil path  124  at the branch point  122   p,  which appropriately secures the amount of lubricating oil to be supplied to the oil cooler  138 . The branch oil path  124  supplies the lubricating oil  152  via oil holes provided in the rotor shaft  28  of the first rotary machine MG 1 , the input shaft  22 , etc., for example, to cool and lubricate the rotor and the bearings of the first rotary machine MG 1  and lubricate gear meshing portions, bearings, etc. of the planetary gear device  24 . 
     The O/P oil path  126  is connected to the discharge side of the O/P pump  58 , and supplies the lubricating oil  152  to a speed reduction unit  128  in which the large speed reduction gear Gr 1 , the small speed reduction gear Gr 2 , the motor output gear Gm etc. are provided, the differential device  48 , etc. The O/P oil path  126  supplies the lubricating oil  152  via a pipe provided separately from the case  60 , an oil hole provided in the case  60 , etc., for example. In the present embodiment, the O/P oil path  126  is mainly constituted of the O/P oil pipe  166  that is provided separately from the case  60  and made of a resin. The O/P oil pipe  166  is disposed in the second housing space  78 , and fixed to the partition wall  76  at a plurality of locations. The lower end portion of the O/P oil pipe  166  is connected to the O/P pump  58  such that the lubricating oil  152  is supplied from the O/P pump  58  to the O/P oil pipe  166 . The upper end portion of the O/P oil pipe  166  reaches a position above the large speed reduction gear Gr 1 , the small speed reduction gear Gr 2 , and the motor output gear Gm. A plurality of projecting nozzle portions  166   a  is provided at the position above the large speed reduction gear Gr 1 , the small speed reduction gear Gr 2 , and the motor output gear Gm to project in a direction parallel to the second axis S 2  and the third axis S 3 . The lubricating oil  152  is discharged from the projecting nozzle portions  166   a  downward or in a horizontal direction such that the lubricating oil  152  is sprayed toward the large speed reduction gear Gr 1 , the small speed reduction gear Gr 2 , the motor output gear Gm, etc. to lubricate gear meshing portions, bearings, etc. thereof. 
     A crank portion  166   b  cranked in parallel with the fourth axis S 4  is provided at an intermediate portion of the O/P oil pipe  166 . The crank portion  166   b  is positioned above the differential device  48  and the differential ring gear Gd. The crank portion  166   b  is provided with a discharge hole to discharge the lubricating oil  152 . The lubricating oil  152  lubricates the differential ring gear Gd, the differential device  48 , bearings, etc. A part of the differential device  48  is immersed in the oil storage portion  150  at the lower part of the case  60  to be lubricated in an oil bath manner, and the lubricating oil  152  is splashed up along with rotation of the differential device  48  such that the lubricating oil  152  is sprayed to lubricate the various portions of the power transfer device  12 . 
       FIG.  5    is a perspective view in which a part of the case  60  in  FIG.  4   , that is, the upper left portion of the partition wall  76  in  FIG.  4   , is illustrated as enlarged, illustrating the vicinity of the connection part  160   c  of the I/P oil pipe  160  being connected to the communication oil hole  76   b  in the partition wall  76 .  FIG.  6    is a sectional view of the power transfer device  12  for a portion corresponding to the VI-VI sectional plane in  FIG.  5   , illustrating the structure of bearings for the rotor shaft  44  and the gear shaft  42  disposed on the third axis S 3  and the connection structure of the I/P oil pipe  160  connected at a position above the third axis S 3 . An end portion of the gear shaft  42  on the second rotary machine MG 2  side is rendered smaller in diameter than the rotor shaft  44 , and fitted into the cylinder of the rotor shaft  44  and coupled so as to be able to transfer power via a spline fitting portion  46 . The rotor shaft  44  is supported by the case  60  so as to be rotatable about the third axis S 3  via a pair of first bearings  92   a  and  92   b  (see  FIG.  1   ). The first bearings  92   a  and  92   b  are disposed on both sides of the rotor of the second rotary machine MG 2  in the axial direction of the rotor shaft  44 . The gear shaft  42  is supported by the case  60  so as to be rotatable about the third axis S 3  via a pair of second bearings  96   a  and  96   b.  The second bearings  96   a  and  96   b  are disposed on both sides of the motor output gear Gm in the axial direction of the gear shaft  42 . The first bearing  92   a  and the second bearing  96   a  are each a ball bearing, and are held as disposed inside a first bearing holding portion  98  and a second bearing holding portion  100 , respectively, in a cylindrical shape and provided as a support portion in the partition wall  76  of the intermediate case member  64 . 
     In order to lubricate the first bearing  92   a  and the second bearing  96   a,  the second bearing holding portion  100  is provided with an oil introduction hole  102  that allows the lubricating oil  152  supplied from the O/P oil pipe  166  to be introduced into the second bearing holding portion  100 . The oil introduction hole  102  is provided above the third axis S 3  so as to penetrate the second bearing holding portion  100  in a cylindrical shape from the outer peripheral side toward the inner peripheral side, and inclined toward the first bearing holding portion  98  with respect to a direction that is orthogonal to the third axis S 3  as the oil introduction hole  102  extends inward, that is, downward, from an outside opening portion on the outer peripheral surface side to open in a portion between the first bearing  92   a  and the second bearing  96   a.  The outside opening portion of the oil introduction hole  102  opens obliquely upward. An oil receiver  104  with a U-shaped or V-shaped section that becomes wider toward the upper side is provided around the opening portion. The lubricating oil  152  discharged downward from the projecting nozzle portions  166   a  of the O/P oil pipe  166  is received by the oil receiver  104 , introduced into the oil introduction hole  102 , and supplied to the portion between the first bearing  92   a  and the second bearing  96   a . That is, one of the plurality of projecting nozzle portions  166   a  provided on the O/P oil pipe  166  is provided directly above the oil receiver  104  as illustrated in  FIG.  6   , and the lubricating oil  152  discharged from the projecting nozzle portion  166   a  flows into the oil introduction hole  102  via the oil receiver  104 . While the oil receiver  104  is open on the distal end side (right side in  FIG.  6   ), a side wall etc. that restricts an outflow of the lubricating oil  152  may be provided as necessary. While the oil receiver  104  is provided integrally with the partition wall  76 , the oil receiver  104  may be constituted separately from the intermediate case member  64  to be retrofitted. 
     On the other hand, the communication oil hole  76   b  to which the connection part  160   c  of the I/P oil pipe  160  is connected is provided at a position directly above the oil receiver  104  in the vertical direction. The communication oil hole  76   b  couples the I/P oil pipe  160  disposed in the second housing space  78  and the MG 2  oil pipe  164  disposed in the third housing space  80  to each other, and is provided in parallel with the third axis S 3 . Countersunk holes  106  and  108  are provided at opening portions on both sides of the communication oil hole  76   b.  The connection part  160   c  of the I/P oil pipe  160  and the MG 2  oil pipe  164  are fitted with the countersunk holes  106  and  108 , respectively. The MG 2  oil pipe  164  is caused to abut against the bottom portion (stepped portion) of the countersunk hole  108  oil-tightly, for example, such that oil does not leak between the communication oil hole  76   b  and the MG 2  oil pipe  164 . A seal member such as an O-ring may be used as necessary. On the other hand, the connection part  160   c  is loosely fitted in the countersunk hole  106  with a predetermined gap at the connection portion  170  such that a predetermined amount of the lubricating oil  152  leaks out and flows downward from the connection portion  170  with the communication oil hole  76   b  even at extremely low temperatures (e.g. −20° C. or lower) at which the viscosity of the lubricating oil  152  is high. Specifically, the connection part  160   c  is fitted without using a seal member such as an O-ring such that a predetermined gap is provided between the bottom portion (stepped portion) of the countersunk hole  106  and the connection part  160   c  and predetermined play is provided between the inner peripheral surface of the countersunk hole  106  and the connection part  160   c.  At least a part of the lubricating oil  152  that has flowed out from the connection portion  170  flows downward along the partition wall  76 , and is received by the oil receiver  104  and flows into the oil introduction hole  102  to be used to lubricate the first bearing  92   a  and the second bearing  96   a.  The oil receiver  104  functions as an oil guide that receives the lubricating oil  152  that has flowed out from the connection portion  170  and guides the lubricating oil  152  into the oil introduction hole  102 . It is also possible to provide the connection part  160   c  at the connection portion  170  with a discharge hole etc., as necessary, such that a predetermined amount of the lubricating oil  152  flows out to be supplied to the oil introduction hole  102  even at extremely low temperatures. 
     In the embodiment, the I/P oil pipe  160  corresponds to the first lubrication pipe, the communication oil hole  76   b  corresponds to the first oil hole, and the second rotary machine MG 2  to be cooled by lubricating oil discharged from the MG 2  oil pipe  164  corresponds to the rotary machine to which the lubricating oil  152  is supplied from the first lubrication pipe by way of the first oil hole. The O/P oil pipe  166  corresponds to the second lubrication pipe, the oil introduction hole  102  corresponds to the second oil hole, and the first bearing  92   a  and the second bearing  96   a  correspond to the bearing member to be lubricated by the lubricating oil  152  supplied from the second lubrication pipe. The case  60  that has the second housing space  78  in which the I/P oil pipe  160  and the O/P oil pipe  166  are disposed corresponds to the case in which the first lubrication pipe and the second lubrication pipe are provided. That is, the bearings  92   a  and  96   a  disposed on the third axis S 3  that is positioned at the highest position in the vehicle among the first axis S 1  to the fourth axis S 4  are not easily sufficiently lubricated by the lubricating oil  152  splashed up by rotation of the differential device  48 , and are located far from the O/P pump  58 . Therefore, the amount of the lubricating oil  152  supplied from the O/P oil pipe  166  alone may be insufficient when the viscosity of the lubricating oil  152  is high at low temperatures and thus the bearings  92   a  and  96   a  may be seized. Therefore, the lubricating oil  152  is made to be supplied also from the I/P oil pipe  160 . 
     In the lubrication structure for the vehicle  10 , that is, the vehicle lubrication system  120 , according to the present embodiment, the connection portion  170  between the I/P oil pipe  160  through which the lubricating oil  152  is supplied to the second rotary machine MG 2  and the communication oil hole  76   b  is located at a position above the opening portion of the oil introduction hole  102  provided in the second bearing holding portion  100  in order to supply the lubricating oil  152  discharged from the O/P oil pipe  166  to the first bearing  92   a  and the second bearing  96   a  such that at least a part of the lubricating oil  152  that has flowed out from the connection portion  170  flows into the oil introduction hole  102 . Therefore, it is possible to suppress a shortage in the amount of the lubricating oil  152  to be supplied to the first bearing  92   a  and the second bearing  96   a  at extremely low temperatures at which the viscosity of the lubricating oil  152  is high. 
     It is only necessary to allow lubricating oil to flow out from the connection portion  170  between the I/P oil pipe  160  and the communication oil hole  76   b,  and to provide the communication oil hole  76   b  at a position above the opening portion of the oil introduction hole  102 . Such a structure can be implemented easily without requiring a significant design change, and can be constituted inexpensively compared to when the O/P pump  58  is increased in size such that a sufficient amount of the lubricating oil  152  is supplied from the O/P oil pipe  166  to the first bearing  92   a  and the second bearing  96   a  even at extremely low temperatures. 
     It is only necessary to loosely fit the connection part  160   c  in the countersunk hole  106  of the communication oil hole  76   b  with a predetermined gap without interposing a seal member such as an O-ring such that the lubricating oil  152  leaks out and flows downward from the connection portion  170  between the connection part  160   c  of the I/P oil pipe  160  and the communication oil hole  76   b.  Such a structure can be implemented easily and inexpensively. 
     The oil receiver  104  is provided at the opening portion of the oil introduction hole  102 , and the connection portion  170  is located at a position directly above the oil receiver  104  in the vertical direction. Therefore, at least a part of the lubricating oil  152  that has flowed downward from the connection portion  170  is received by the oil receiver  104  and allowed to reliably flow into the oil introduction hole  102 , which appropriately suppresses a shortage in the amount of the lubricating oil  152  to be supplied to the first bearing  92   a  and the second bearing  96   a.    
     The lubrication structure includes the I/P pump  56  mechanically rotationally driven by the engine  16  and the O/P pump  58  coupled to the differential device  48  which is an output portion and to be mechanically rotationally driven, the lubricating oil  152  is supplied from the I/P pump  56  to the I/P oil pipe  160 , and the lubricating oil  152  is supplied from the O/P pump  58  to the O/P oil pipe  166 . Therefore, the amount of lubricating oil to be supplied from the O/P oil pipe  166  to the first bearing  92   a  and the second bearing  96   a  is decreased with the discharge amount of the O/P pump  58  reduced at low vehicle speeds. However, a part of the lubricating oil  152  supplied from the I/P pump  56  to the I/P oil pipe  160  flows out from the connection portion  170  with the communication oil hole  76   b  and flows into the oil introduction hole  102 , which suppresses a shortage in the amount of the lubricating oil  152  to be supplied to the first bearing  92   a  and the second bearing  96   a  at low vehicle speeds. 
     The discharge capacity of the I/P pump  56  is larger than the discharge capacity of the O/P pump  58 , and the I/P pump  56  with a larger discharge capacity is less affected by the viscosity of the lubricating oil  152 . Therefore, a sufficient amount of the lubricating oil  152  can be supplied to the second rotary machine MG 2  to appropriately cool the second rotary machine MG 2  even at extremely low temperatures at which the viscosity of the lubricating oil  152  is high. In addition, a part of the lubricating oil  152  is caused to flow into the oil introduction hole  102  to be supplied to the first bearing  92   a  and the second bearing  96   a,  which appropriately provides the effect of suppressing a shortage in the amount of the lubricating oil  152  to be supplied to the first bearing  92   a  and the second bearing  96   a  without increasing the O/P pump  58  in size. 
     Next, another embodiment of the present disclosure will be described. Portions according to the following embodiment that are substantially the same as those according to the above embodiment are given like signs to omit detailed description. 
       FIG.  7    is a perspective view corresponding to  FIG.  5   , illustrating the upper left portion of the partition wall  76  at which the communication oil hole  76   b  to which the connection part  160   c  of the I/P oil pipe  160  is connected and the oil introduction hole  102  for supplying the lubricating oil  152  to the first bearing  92   a  and the second bearing  96   a  are provided. In the embodiment, the position of the outside opening portion of the oil introduction hole  102  is different from that in the above embodiment. The outside opening portion is located off a position directly below the communication oil hole  76   b  to which the connection part  160   c  is connected, and an oil guide  172  in an inclined gutter shape is provided directly below the communication oil hole  76   b  to guide the lubricating oil  152  that has flowed downward from the connection portion  170  between the communication oil hole  76   b  and the connection part  160   c  to the oil introduction hole  102 . In this case, it is desirable that the projecting nozzle portions  166   a  of the O/P oil pipe  166  should be located directly above the oil introduction hole  102 . However, the projecting nozzle portions  166   a  may be located at any position above the oil guide  172  as long as the lubricating oil  152  that has flowed downward is received by the oil guide  172 . A plurality of oil introduction holes  102  may be provided. Also with the present embodiment, substantially the same effect and function as those according to the above embodiment can be obtained. 
       FIG.  8    is a block diagram corresponding to  FIG.  2   , illustrating a vehicle lubrication system  200  that includes an second O/P oil path  202  that couples the O/P pump  58  and the I/P oil path  122  to each other as indicated by the dashed line such that a part of the lubricating oil  152  discharged from the O/P pump  58  is supplied to the I/P oil path  122 . While the second O/P oil path  202  is constituted of a pipe such as a resin pipe, for example, the second O/P oil path  202  may be constituted of an oil hole provided in a side wall etc. of the case  60 . The second O/P oil path  202  is provided separately from the O/P oil path  126 , and the O/P oil path  126  is provided with an orifice  142  that restricts the amount of lubricating oil that flows into the O/P oil path  126 , which appropriately secures the amount of lubricating oil to be supplied from the second O/P oil path  202  to the I/P oil path  122 . 
     The second O/P oil path  202  is coupled to a merge point  122   j  provided between the branch point  122   p  and the relief position  122   r  of the I/P oil path  122 . A check valve  204  is provided before the merge point  122   j  to allow a flow of the lubricating oil  152  toward the merge point  122   j  but block a flow in the opposite direction. A check valve  206  is also provided before the merge point  122   j  of the I/P oil path  122  to allow a flow of the lubricating oil  152  toward the merge point  122   j  but block a flow in the opposite direction. Consequently, the lubricating oil  152  on the high pressure side in the I/P oil path  122  and the second O/P oil path  202  is supplied from the merge point  122   j  to the rotary machines MG 1  and MG 2  by way of the oil cooler  138 . That is, when operation of the I/P pump  56  is stopped as rotation of the engine  16  is stopped in the BEV travel mode, a part of the lubricating oil  152  discharged from the O/P pump  58  is supplied from the second O/P oil path  202  to the rotary machines MG 1  an MG 2  by way of the I/P oil path  122 . Therefore, the second rotary machine MG 2  that is used as a drive force source is cooled appropriately. In other words, it is possible to improve fuel efficiency by extending the travel time in the BEV travel mode in which rotation of the engine  16  is stopped, which is suitably applied to a hybrid electric vehicle of a plug-in kind that can be charged externally. The check valves  204  and  206  can be incorporated in a common valve body  208  together with the relief valve  134 , for example. 
     In the present embodiment, the O/P oil path  126  is provided with the orifice  142 . Therefore, there is a growing fear of a shortage in the amount of lubricating oil to be supplied from the O/P oil path  126  to the first bearing  92   a  and the second bearing  96   a  at extremely low temperatures at which the viscosity of the lubricating oil  152  is high. In contrast, the lubricating oil  152  flows out from the connection portion  170  between the I/P oil pipe  160  of the I/P oil path  122  through which the lubricating oil  152  is supplied to the second rotary machine MG 2  and the communication oil hole  76   b,  and flows into the oil introduction hole  102  to be supplied to the first bearing  92   a  and the second bearing  96   a . Therefore, a remarkable effect of suppressing a shortage in the amount of the lubricating oil  152  to be supplied to the first bearing  92   a  and the second bearing  96   a  can be obtained without increasing the O/P pump  58  in size. 
     While embodiments of the present disclosure have been described in detail above, these are merely exemplary, and the present disclosure can be implemented in aspects with a variety of modifications and improvements applied based on the knowledge of a person skilled in the art.