Patent Publication Number: US-2016230850-A1

Title: Power transmitting apparatus for hybrid vehicle

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a power transmitting apparatus on which a hybrid vehicle including two or more sources of driving force having different dynamic power generation principles is installed. 
     2. Description of Related Art 
     A hybrid vehicle includes two or more driving sources having difference dynamic power generation principles, as sources of driving force for traveling the vehicle. The driving sources include, for example, an engine that generates dynamic power by converting thermal energy to kinetic energy, and a rotary machine (e. g., electric motor) having an energy regeneration capability. For example, an internal combustion engine, such as a gasoline engine or a diesel engine, and a rotary machine, such as an electric motor that functions as a generator, or a hydraulic motor that functions as an accumulator, may be installed on the hybrid vehicle. By utilizing respective characteristics possessed by the engine and the rotary machine, it is possible to improve the energy efficiency and reduce exhaust gas or emissions. One example of hybrid drive system for use in this type of hybrid vehicle is described in Japanese Patent Application Publication No. 2008-120234 (JP 2008-120234 A). 
     The hybrid drive system described in JP 2008-120234 A includes an engine, a first motor having a function of generating electric power using dynamic power of the engine, and a second motor that generates dynamic power to an output member using the electric power generated by the first motor. The first motor and the second motor are disposed on the same axis, and a power split mechanism that distributes the dynamic power generated by the engine to the first motor and the output member is disposed between the first motor and the second motor. Furthermore, in the hybrid drive system described in JP 2008-120234 A, a transmission gear device that changes the rotational speed of the engine and transmits torque to the power split mechanism is disposed between the first motor and the second motor. 
     In Japanese Patent Application Publication No. 2008-265598 (JP 2008-265598 A), a hybrid vehicle including an engine, a first motor, a second motor, and a power split mechanism constituted by a planetary gear unit having three rotation elements is described. The hybrid vehicle described in JP 2008-265598 A further includes a clutch that fixes an output shaft of the engine so as to make the output shaft unable to rotate. The first motor is connected to the output shaft of the engine via the power split mechanism, and the second motor is connected to drive wheels. Operations of the engine, first motor, second motor, and the clutch are respectively controlled according to the required driving force of the vehicle. When the clutch is engaged, and the output shaft of the engine is fixed, the hybrid vehicle is able to travel in a motor traveling mode in which both the first motor and the second motor are driven, in a condition where the power split mechanism functions as a speed reducing mechanism or a speed increasing mechanism. 
     Also, a hybrid vehicle similar in construction to the hybrid vehicle described in JP 2008-265598 A as described above is described in Japanese Patent Application Publication No. 2008-265600 (JP 2008-265600 A). In the hybrid vehicle described in JP 2008-265600 A, when a condition or conditions under which the clutch is engaged to fix the crankshaft of the engine so as to make it unable to rotate is/are satisfied, the operation of the engine is stopped, and rotations of two motors are respectively controlled, using a map that specifies torque split with which the two motors are most efficiently driven, based on the accelerator operation amount, vehicle speed, and the speed ratio of the transmission gear device. 
     SUMMARY OF THE INVENTION 
     By adding a transmission gear mechanism (e.g., a transmission gear device) for changing the rotational speed of the engine to the arrangement of a known power transmitting apparatus for a hybrid vehicle including the engine, electric motor, and the power split mechanism, as in the hybrid drive system described in JP 2008-120234 A, it is possible to operate the engine at a rotational speed that is more advantageous to the fuel efficiency, according to the required driving force and traveling conditions. Consequently, the energy efficiency of the hybrid vehicle can be improved. 
     The transmission gear mechanism as described above includes a gear train, and friction devices (friction engagement devices), such as a clutch and a brake, for shift control. The friction devices, such as a clutch and a brake, are generally arranged to be controlled by use of hydraulic pressure. Namely, each of the friction devices included in the transmission gear mechanism as described above includes a plurality of friction members, and a hydraulic actuator for operating the friction members, and the friction members are arranged to engage with each other when a given hydraulic pressure is supplied to the hydraulic actuator. In the known arrangement, the hydraulic pressure is generally supplied to the hydraulic actuator, via an oil passage formed in the interior of a rotary shaft of the power transmitting apparatus. 
     When the hydraulic pressure is supplied to the hydraulic actuator via the oil passage formed within the rotary shaft as described above, a seal ring for preventing hydraulic leak is used at a connecting portion between the oil passage formed in the rotary shaft and an oil passage that communicate with the hydraulic actuator. The seal ring is provided between the outer periphery of the rotary shaft, and the inner periphery of a member that rotates relative to the rotary shaft. Accordingly, if the number of locations where the seal ring is used is increased, a dragging loss increases at sliding portions of the seal rings, and the energy efficiency of the system may be reduced. 
     The present invention provides a power transmitting apparatus for a hybrid vehicle which exhibits a high energy efficiency, even if the system is provided by adding a transmission gear mechanism for changing the rotational speed of an engine to the known system. 
     One aspect of the invention relates to a power transmitting apparatus for a hybrid vehicle including an engine as drive source, and a hydraulic actuator. The power transmitting apparatus includes at least one rotary machine, a power split mechanism, a housing, a transmission gear mechanism, a front cover, and a rotary machine cover. The above-indicated at least one rotary machine is a drive source of the hybrid vehicle. The power split mechanism is a differential mechanism having a first rotation element, a second rotation element to which the rotary machine is coupled, and a third rotation element to which a drive shaft is coupled. The power split mechanism is configured to split or combine dynamic power among the sources of driving force and the drive shaft and transmit the split or combined dynamic power to the sources of driving force or the drive shaft. The power split mechanism and the at least one rotary machine are disposed in the housing. The transmission gear mechanism has a friction device that is engaged or disengaged by the hydraulic actuator. The transmission gear mechanism is configured to change a rotational speed of the engine through engagement and disengagement of the friction device, and transmit torque of the engine to the first rotation element. The front cover covers one side of the transmission gear mechanism closer to the engine. The rotary machine cover covers the other side of the transmission gear mechanism closer to the power split mechanism. The transmission gear mechanism is disposed inside the front cover. The transmission gear mechanism is covered with the front cover and the rotary machine cover. The transmission gear mechanism, the front cover, and the rotary machine cover is a transmission gear unit. The transmission gear unit is provided to an end portion of the housing closer to the transmission gear mechanism. The oil passage for shift control is provided in the front cover or the rotary machine cover. The hydraulic pressure is supplied to the hydraulic actuator through the oil passage for the shift control. 
     In the power transmitting apparatus as described above, the friction device may include a clutch and a brake. The transmission gear mechanism may include a single planetary gear unit. The clutch may be configured to selectively connect a sun gear of the single planetary gear unit to a carrier of the single planetary gear unit. The brake may be configured to selectively fix the sun gear so as to make the sun gear unable to rotate. The oil passage for the shift control may include at least one of a communication hole and a tubular member. The communication hole may be provided in an interior of the front cover. The tubular member may be shaped along a shape of the front cover. 
     In the power transmitting apparatus as described above, the friction device may include a clutch and a brake. The transmission gear mechanism may include a double planetary gear unit. The clutch may be configured to selectively connect a sun gear of the double planetary gear unit to a carrier of the double planetary gear unit. The brake may be configured to selectively fix the sun gear so as to make the sun gear unable to rotate. The oil passage for the shift control may include at least one of a communication hole and a tubular member. The communication hole may be provided in an interior of the rotary machine cover. The tubular member may be shaped along a shape of the rotary machine cover. 
     In the power transmitting apparatus as described above, the transmission gear unit may be provided to the housing such that the oil passage for the shift control is connected to a supply oil passage. The supply oil passage may be provided in the housing. A hydraulic pressure may be supplied from a hydraulic source to the supply oil passage. 
     In the power transmitting apparatus according to the above aspect of the invention, the transmission gear mechanism for changing the rotational speed of the engine by hydraulically controlling the friction device with the hydraulic actuator is provided between the engine and the power split mechanism. The transmission gear mechanism is housed in the front cover and the rotary machine cover, to provide an integral transmission gear unit, against the housing as a principal part of the power transmitting apparatus in which the power split mechanism, rotary machine, etc. are disposed. Accordingly, the speed changing mechanism including the friction device and the hydraulic actuator can be handled as a sub-assembly. 
     In the power transmitting apparatus according to the above aspect of the invention, the oil passage for shift control, through which hydraulic pressure is supplied to the hydraulic actuator for hydraulic control of the speed changing mechanism, is provided in the front cover or rotary machine cover in which the speed changing mechanism is housed. For example, the oil passage for shift control is provided by a communication hole formed by drilling or boring in the interior of the front cover or rotary machine cover. 
     In another example, the oil passage for shift control is provided by a tubular member, such as a metal pipe, formed by bending along the shape of the front cover or rotary machine cover. The oil passages as described above are arranged to communicate with a supply oil passage formed in the housing, no matter how each oil passage is formed, in a condition where the transmission gear unit including the transmission gear mechanism is mounted to the housing. The supply oil passage of the housing is an oil passage through which hydraulic pressure for hydraulically controlling the friction device is supplied from the hydraulic source. Therefore, the hydraulic pressure for shift control is supplied to the hydraulic actuator of the friction device, via the supply oil passage of the housing, and the oil passage for shift control formed in the front cover or the rotary machine cover. 
     Accordingly, in the power transmitting apparatus according to the above aspect of the invention, the oil passage for shift control, through which the hydraulic pressure is supplied to the hydraulic actuator of the speed changing mechanism for hydraulic control of the speed changing mechanism, is formed in the front cover or rotary machine cover in which the transmission gear mechanism is housed. Namely, the oil passage for shift control is not formed in the interior of rotary shafts of the power transmitting apparatus, but formed in the front cover or the rotary machine cover. In the related art, the power transmitting apparatus for vehicle of this type is generally configured such that oil passages formed in the interior of the rotary shafts are used for supplying hydraulic oil for control of friction devices (friction mechanism), etc., and lubricating oil for lubrication or cooling of respective parts of the system. On the other hand, in the power transmitting apparatus according to the invention, the oil passage for shift control, through which the hydraulic pressure for shift control is supplied, is not formed within the rotary shaft of the power transmitting apparatus, but formed in the front cover or the rotary machine cover. Therefore, the oil passages formed within the rotary shafts as in the related art can be exclusively used for lubricating oil having a lower pressure than the control hydraulic pressure. As a result, the arrangement of oil passages formed within the rotary shafts can be simplified. While seal rings for preventing or curbing hydraulic leak need to be used when the oil passages are formed within the rotary shafts, the number of the seal rings used for the rotary shafts can be reduced, since the oil passage for shift control is formed in the front cover or the rotary machine cover. Therefore, the dragging loss that would appear at sliding portions of the seal rings during rotation of the rotary shaft can be reduced. Consequently, the energy efficiency of the power transmitting apparatus can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a skeleton diagram useful for explaining a drive train of a hybrid vehicle to which this invention is applied, showing an example of drive train suitable for installation on an FR-type vehicle, wherein a transmission gear mechanism is constituted by a single pinion type planetary gear unit; 
         FIG. 2  is a skeleton diagram useful for explaining a driven train of a hybrid vehicle to which this invention is applied, showing an example of drive train suitable for installation on an FF-type vehicle, wherein a transmission gear mechanism is constituted by a single pinion type planetary gear unit; 
         FIG. 3  is a table indicating operating states of a clutch, a brake, and first and second motor-generators, in each driving state of the drive train shown in  FIG. 1  or  FIG. 2 ; 
         FIG. 4  is a nomographic chart in connection with a power split mechanism and a transmission gear mechanism in the drive train shown in  FIG. 1  or  FIG. 2 , showing a condition where the vehicle travels only with the output of the second motor-generator; 
         FIG. 5  is a nomographic chart in connection with the power split mechanism and the transmission gear mechanism in the drive train shown in  FIG 1  or  FIG. 2 , showing a condition where the vehicle travels with the outputs of both of the first motor-generator and the second motor-generator; 
         FIG. 6  is a nomographic chart in connection with the power split mechanism and the transmission gear mechanism in the drive train shown in  FIG 1  or  FIG. 2 , showing a condition where the speed changing mechanism is set in an O/D speed position (High); 
         FIG. 7  is a nomographic chart in connection with the power split mechanism and the transmission gear mechanism in the drive train shown in  FIG. 1  or  FIG. 2 , showing a condition where the transmission gear mechanism is set in a direct-coupling speed position (Low); 
         FIG. 8  is a block diagram useful for explaining a control system of the hybrid vehicle to which this invention is applied; 
         FIG. 9  is a map (graph) used in control of the operation of the hybrid vehicle to which this invention is applied, and shift control of the transmission gear mechanism, showing an engine traveling range and a motor traveling range; 
         FIG. 10  is a skeleton diagram useful for explaining a drive train of a hybrid vehicle to which this invention is applied, showing an example of drive train suitable for installation on an FR-type vehicle, wherein a transmission gear mechanism is constituted by a double pinion type planetary gear unit; 
         FIG. 11  is a skeleton diagram useful for explaining a drive train of a hybrid vehicle to which this invention is applied, showing an example of drive train suitable for installation on an FF-type vehicle, wherein a transmission gear mechanism is constituted by a double pinion type planetary gear unit; 
         FIG. 12  is a cross-sectional view useful for specifically explaining the construction of a power transmitting apparatus for a hybrid vehicle according to this invention, showing an example in which a transmission gear mechanism is constituted by a single pinion type planetary gear unit; and 
         FIG. 13  is a cross-sectional view useful for specifically explaining the construction of a power transmitting apparatus for a hybrid vehicle according to this invention, showing an example in which a transmission gear mechanism is constituted by a double pinion type planetary gear unit. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Next, this invention will be specifically described with reference to the drawings. The power transmitting apparatus according to the invention is installed on a vehicle including an engine that generates dynamic power by converting thermal energy to kinetic energy, and a rotary machine capable of energy regeneration, as sources of driving force, namely, a hybrid vehicle including two or more sources of driving force having different dynamic power generation principles. 
     A gasoline engine is most commonly used as the engine included in the hybrid vehicle. Other than the gasoline engine, an internal combustion engine, such as a diesel engine or an LPG engine, which uses a fuel other than gasoline, may be used as the engine included in the invention. On the other hand, a motor having a power generating capability (i.e., a motor-generator) is most commonly used as the rotary machine. Other than the motor-generator, a pressure motor having the function of accumulating pressure, such as hydraulic pressure or pneumatic pressure, a flywheel capable of storing and releasing rotational energy, or the like, may be used as the rotary machine included in the invention. 
     The hybrid vehicle to which this invention is applied is configured to operate in a traveling mode selected from “engine traveling mode” in which the vehicle travels with dynamic power generated by the engine, “HV (hybrid) traveling mode”, and a traveling mode in which the vehicle travels with dynamic power generated by the rotary machine. In the case where a motor is used as the rotary machine, in particular, the traveling mode of the hybrid vehicle may be selected from “engine traveling mode”, and “motor traveling mode” in which the vehicle travels with the motor driven by electric power stored in a battery. 
       FIG. 1  shows one example of power train of the hybrid vehicle to which this invention is applied. The example shown in  FIG. 1  is a so-called two-motor-type hybrid vehicle Ve using an engine (ENG)  1 , and two rotary machines in the form of a first motor-generator (MG 1 )  2  and a second motor-generator (MG 2 )  3 , as sources of driving force. The hybrid vehicle Ve has a power split mechanism  4  that divides or splits dynamic power generated by the engine  1 , and transmits the dynamic power to one side closer to the first motor-generator  2  and the other side close to drive shafts  5 . The hybrid vehicle Ve is also operable such that electric power generated by the first motor-generator  2  is supplied to the second motor-generator (MG 2 )  3 , and dynamic power generated by the second motor-generator  3  by use of the electric power can be added to power received by the drive shafts  5 . 
     The power split mechanism  4  is constituted by a differential mechanism having three rotation elements. More specifically, the power split mechanism  4  is constituted by a planetary gear unit having a sun gear  6  as a first rotation element, a carrier  8  as a second rotation element, and a ring gear  7  as a third rotation element. In the example shown in  FIG. 1 , a single-pinion-type planetary gear unit is used. 
     The planetary gear unit that constitutes the power split mechanism  4  is disposed on the same axis as the engine  1 . The first motor-generator  2  is coupled to the sun gear  6  of the planetary gear unit. Namely, a rotor  2 a of the first motor-generator  2  is coupled with the sun gear  6 . The ring gear  7  is disposed concentrically with respect to the sun gear  6 . A pinion gear that meshes with the sun gear  6  and the ring gear  7  is held by the carrier  8  such that the pinion gear can rotate about its own axis and rotate about the axis of the power split mechanism  4 . An output shaft la of the engine  1  is coupled to the carrier  8 , via a transmission gear mechanism  17  (which will be described later). A propeller shaft  9  has one end portion that is coupled to the ring gear  7 . The other end portion of the propeller shaft  9  is connected to the drive shafts  5  and drive wheels  11 , via a differential gear  10 . 
     The power train of the hybrid vehicle as shown in  FIG. 1  is configured to add torque produced by the second motor-generator  3 , to torque transmitted from the power split mechanism  4  to the propeller shaft  9  and the drive wheels  11 . More specifically, the second motor-generator  3  is disposed on the same rotational axis as the engine  1 , and the second motor-generator  3  is connected to the propeller shaft  9  via a gear train  12 . 
     In the example shown in  FIG. 1 , a single pinion type planetary gear unit is used as the gear train  12 . A sun gear  13  of the planetary gear unit that constitutes the gear train  12  is coupled to a rotor  3   a  of the second motor-generator  3 . A carrier  14  of the gear train  12  is coupled to the propeller shaft  9 . A ring gear  15  of the gear train  12  is fixed to a stationary member  16 , such as a casing, such that the ring gear  15  cannot rotate. Namely, in the gear train  12 , the ring gear  15  is a fixed element. The carrier  14  that serves as an output element when the sun gear  13  is an input element is adapted to rotate at a lower speed than the sun gear  13 , in the same direction as the sun gear  13 . Accordingly, the gear train  12  functions as a speed reducing mechanism when it generates torque applied to the sun gear  13 , from the carrier  14 . Namely, the gear train  12  is arranged to amplify torque applied from the second motor-generator  3  to the sun gear  13 , and transmit the resulting torque to the propeller shaft  9 . 
     The first motor-generator  2  and the second motor-generator  3  are respectively connected to a battery, via controllers, such as inverters (not shown). In operation, electric current passed through each of the first motor-generator  2  and the second motor-generator  3  is controlled so that each motor-generator  2 ,  3  functions as a motor or a generator. On the other hand, the engine  1  is controlled through control of its throttle opening and ignition timing. Also, automatic stop of combustion operation of the engine  1 , and start and re-start of the engine  1 , are controlled. 
     In the hybrid vehicle Ve to which the invention is applied, the transmission gear mechanism  17  is provided between the engine  1 , and the power split mechanism  4  and first motor-generator  2 . The transmission gear mechanism  17  is arranged to be switched to one of a direct-coupling speed position, and a speed-increase speed position or overdrive (O/D) speed position. In the example shown in  FIG. 1 , the transmission gear mechanism  17  is constituted by a single pinion type planetary gear unit  17   a  having a carrier  18 , a ring gear  19 , and a sun gear  20 . The carrier  18  is coupled to the output shaft la of the engine  1 . The ring gear  19  is coupled to the carrier  8  of the power split mechanism  4  as described above so as to rotate as a unit with the carrier  8 . A clutch C 1  for selectively coupling the sun gear  20  with the carrier  18  is provided between the sun gear  20  and the carrier  18 . A brake B 1  is provided for selectively fixing the sun gear  20  in a non-rotatable state. The clutch C 1  and the brake B 1  may be constituted by friction devices that are hydraulically engaged and released, for example. 
     In the transmission gear mechanism  17 , when the clutch C 1  is engaged, the sun gear  20  and the carrier  18  of the planetary gear unit  17   a  are coupled to each other. As a result, the whole planetary gear unit  17   a  rotates as a unit, and is thus placed in a so-called directly connected state in which no speed increasing effect nor speed reducing effect is produced. When the brake B 1  as well as the clutch C 1  is engaged, the whole planetary gear unit  17   a  is fixed as a unit, and rotation of the carrier  8  of the power split mechanism  4  and rotation of the engine  1  are stopped. On the other hand, when only the brake B 1  is engaged, the sun gear  20  of the transmission gear mechanism  17  becomes a fixed element, and the carrier  18  becomes an input element. Therefore, the ring gear  19  that becomes an output element when the carrier  18  is the input element rotates at a higher speed than the carrier  18 , in the same direction as the carrier  18 . Accordingly, the transmission gear mechanism  17  functions as a speed increasing mechanism. Namely, the transmission gear mechanism  17  is placed in the O/D speed position. 
     In the example of the hybrid vehicle Ve shown in  FIG. 1 , drive torque generated from one or more sources of driving force is transmitted to the drive shafts  5  and the drive wheels  11  via the propeller shaft  9 . Namely, the drive train of the hybrid vehicle Ve is suitable for installation on a so-called FR-type vehicle in which the sources of driving force are located in a front part of the vehicle, and the driving force is generated at the rear wheels. Meanwhile, this invention may also be applied to a so-called FF-type vehicle in which the sources of driving force are located in a front part of the vehicle, and the driving force is generated at the front wheels. An example of the drive train suitable for installation on the FF-type vehicle is illustrated in  FIG. 2 . 
     As in the above-described example shown in  FIG. 1 , the hybrid vehicle Ve shown in  FIG. 2  includes the engine  1 , and the first motor-generator  2  and second motor-generator  3 , as sources of driving force. The hybrid vehicle Ve also includes the transmission gear mechanism  17 , power split mechanism  4 , and the gear train  12 . The transmission gear mechanism  17  is constituted by the single pinion type planetary gear unit  17   a , clutch C 1 , and the brake B 1 , as in the example shown in  FIG. 1 . The output shaft  1   a  of the engine  1  is coupled to the carrier  18  of the planetary gear unit  17   a . The carrier  8  of the power split mechanism  4  is coupled to the ring gear  19 . In the example shown in  FIG. 2 , a drive gear  25  is coupled to the ring gear  7  of the power split mechanism  4 . Also, the gear train  12  consists of the above-mentioned drive gear  25 , counter shaft  26 , counter driven gear  27 , reduction gear  28 , and a differential drive gear  29 . 
     More specifically, the counter shaft  26  is disposed in parallel with the rotational axis of the engine  1 , power split mechanism  4 , etc. The counter driven gear  27  that engages with the drive gear  25  is mounted so as to rotate as a unit with the counter shaft  26 . Furthermore, the power train of  FIG. 2  is configured such that torque produced by the second motor-generator  3  can be added to torque transmitted from the power split mechanism  4  to the drive shafts  5 . Namely, the second motor-generator  3  is disposed in parallel with the counter shaft  26 , and the reduction gear  28  coupled to the rotor  3   a  is in meshing engagement with the counter driven gear  27 . The reduction gear  28  has a smaller diameter than the counter driven gear  27 . Accordingly, the gear train  12  functions as a speed reducing mechanism when it transmits torque applied to the reduction gear  28  to the counter shaft  26  via the counter driven gear  27 . Namely, the gear train  12  is arranged to amplify the torque produced by the second motor-generator  3  and transmit the resulting torque to the counter shaft  26 . 
     The differential drive gear  29  is mounted on the counter shaft  26  so as to rotate together with the counter shaft  26 . Also, in the example shown in  FIG. 2 , a ring gear  30  is formed in an outer peripheral portion of the differential gear  10 . The differential drive gear  29  is in meshing engagement with the ring gear  30  formed in the differential gear  10 . Accordingly, torque applied to the power split mechanism  4  and generated from the ring gear  7 , and torque generated from the second motor-generator  3 , are transmitted to the drive shafts  5  and the drive wheels  11 , via the gear train  12  and the differential gear  10 . In  FIG. 2 , the position of the differential gear  10  is shifted to the right in  FIG. 2 , for the sake of convenience in drawing of  FIG. 2 . 
     The table of  FIG. 3  shows engaged/released states of the clutch C 1  and the brake B 1 , and the operating states of the first motor-generator  2  and the second motor-generator  3 , when the hybrid vehicle Ve as shown in  FIG. 1  or  FIG. 2  is traveling forward and backward in each of the above-indicated traveling modes. Each operating state of the hybrid vehicle Ve will be briefly explained. In  FIG. 3 , “EV” denotes “motor traveling mode”. In “single motor traveling mode”, both of the clutch C 1  and the brake B 1  are released. Then, the second motor-generator  3  is operated as a motor (M), and the first motor-generator  2  functions as a generator (G). In this case, the first motor-generator  2  may run idle. This operating state is illustrated in the nomographic chart of  FIG. 4 . To produce an engine brake effect in the “single motor traveling mode”, one of the clutch C 1  and the brake B 1  is engaged, so that the rotational speed of the ring gear  7  in the power split mechanism  4  is reduced. 
     In “double motor traveling mode” as another type of the motor traveling mode as described above, both of the first motor-generator  2  and the second motor-generator  3  function as motors. In this mode, the clutch C 1  and the brake B 1  are both engaged, and the carrier  8  of the power split mechanism  4  is fixed in a non-rotatable state, so that torque produced by the first motor-generator  2  is transmitted to the drive shafts  5 . The gear ratios between rotation elements of the power split mechanism  4  are set so that the power split mechanism  4  functions as a speed reducer in this condition. Accordingly, in this case, the torque produced by the first motor-generator  2  is amplified, and transmitted from the ring gear  7  of the power split mechanism  4  to the propeller shaft  9 . This operating state is illustrated in the nomographic chart of  FIG. 5 . 
     In the table of  FIG. 3 , “HV” denotes “hybrid traveling mode” in which the engine  1  is driven. Where the vehicle Ve is traveling at a light load and a middle to high speed, the transmission gear mechanism  17  is set in the O/D state (High). Namely, the clutch C 1  is released, and the brake B 1  is engaged. This operating state is illustrated in the nomographic chart of  FIG. 6 . In this state, the engine speed is controlled by the first motor-generator  2  to a rotational speed that provides high fuel efficiency, as described above. In this case, electric power generated by the first motor-generator  2  that functions as a generator is supplied to the second motor-generator  3 . As a result, the second motor-generator  3  operates as a motor, and generates driving torque. When large driving force is required, such as when the vehicle travels at a low speed and the accelerator operation amount is increased, the transmission gear mechanism  17  is controlled to the directly connected state (Low). Namely, the clutch C 1  is engaged, and the brake B 1  is released. As a result, the whole transmission gear mechanism  17  rotates as a unit. This operating state is illustrated in the nomographic chart of  FIG. 7 . In this case, too, the first motor-generator  2  is operated as a generator, and the second motor-generator  3  is operated as a motor, as in the case of the O/D state (High). 
     An electronic control unit (ECU)  21  is provided for controlling operation of the engine  1 , operation of the first motor-generator  2  and the second motor-generator  3 , and controlling engagement and release of the clutch C 1  and the brake B 1 . A control system of the ECU  21  is illustrated in the block diagram of  FIG. 8 . 
     The ECU  21  includes a hybrid control unit (HV-ECU)  22  for performing overall control for traveling the hybrid vehicle, a motor-generator control unit (MG-ECU)  23  for controlling the first motor-generator  2  and the second motor-generator  3 , and an engine control unit (E/G-ECU)  24  for controlling the engine  1 , for example. Each of these control units  22 ,  23 ,  24  is mainly comprised of a microcomputer, and is configured to perform computations using input data and pre-stored data, and output the results of computations as control command signals. 
     Examples of input data received by the ECU  21  will be listed below. For example, the HV-ECU  22  receives the vehicle speed, the accelerator operation amount, the rotational speed of the first motor-generator  2 , the rotational speed of the second motor-generator  3 , the rotational speed of the ring gear  7  (output shaft speed), the rotational speed of the engine  1 , the SOC of the battery, and so forth. Examples of output data generated from the ECU  21  will be listed below. For example, the HV-ECU  22  outputs a torque command value for the first motor-generator  2 , a torque command value for the second motor-generator  3 , a torque command value for the engine  1 , a hydraulic command value PC 1  for the clutch C 1 , a hydraulic command value PB 1  for the brake B 1 , and so forth. 
     The MG-ECU  23  receives the torque command value for the first motor-generator  2  and the torque command value for the second motor-generator  3 , as control data. Then, the MG-ECU  23  is configured to output current command signals to the first motor-generator  2  and the second motor-generator  3 . Also, the E/G-ECU  24  receives the engine torque command signal as control data. Then, the E/G-ECU  24  is configured to perform computations based on the engine torque command signal, and output a throttle opening signal to an electronic throttle valve (not shown), an ignition signal for controlling the ignition timing, and so forth. 
     The engine  1 , the first motor-generator  2 , and the second motor-generator  3 , which provide the sources of driving force of the hybrid vehicle Ve as described above, have different dynamic power performances and driving characteristics. For example, the engine  1  is able to operate in a wide operating range from a low-torque, low-speed range to a high-torque, high-speed range. Also, the energy efficiency of the engine  1  is good in an operating range in which the torque and the rotational speed are relatively high. On the other hand, the first motor-generator  2  is characterized by producing large torque at a low rotational speed, so as to perform control for adjusting the rotational speed of the engine  1 , the crank angle at the time of stopping the engine  1 , etc., and generate driving force The second motor-generator  3  can operate at a higher rotational speed that the first motor-generator  2 , so as to generate torque to the drive shafts  5 , and has a characteristic that the maximum torque is smaller than that of the first motor-generator  2 . 
     The hybrid vehicle Ve, which includes the engine  1 , the first motor-generator  2  and the second motor-generator  3 , as sources of driving force, is controlled so as to provide high energy efficiency and high fuel efficiency, by effectively utilizing these sources of driving force. Namely, one of the “engine traveling mode” in which the vehicle travels with output of the engine  1 , and the “motor traveling mode” in which the vehicle travels with output of at least one of the first motor-generator  2  and the second motor-generator  3 , is selected and established according to the traveling conditions of the hybrid vehicle Ve. 
     The map of  FIG. 9  shows operating ranges in which the respective traveling modes as described above are set. In  FIG. 9  indicating the operating ranges of the vehicle Ve, the horizontal axis indicates the vehicle speed, and the vertical axis indicates the required driving force. A range denoted by symbol  1  is an engine traveling range in which the “engine traveling mode” is executed, and a range denoted by symbol II is a motor traveling range in which the “motor traveling mode” is executed. In the engine traveling range I, a line of threshold values T is set which partitions this range I into a range in which the transmission gear mechanism  17  is controlled to the directly connected state (Low), and a range in which the transmission gear mechanism  17  is controlled to the O/D state (High). Thus, the traveling mode and the speed position of the transmission gear mechanism  17  are selected and set according to the required driving force required of the hybrid vehicle Ve. For example, if an operating point determined by the vehicle speed and the required driving force moves from the range of the directly connected state (Low) to the range of the O/D state (High), as indicated by arrow “a” in  FIG. 9 , the transmission gear mechanism  17  is shifted from the directly connected state (Low) to the O/D state (High). The ECU  21  as described above is configured to carry out control for switching the traveling mode and switching the speed position in the transmission gear mechanism  17 , according to change of the operating range or operating point as described above. 
     In the examples of hybrid vehicles Ve shown in  FIG. 1  and  FIG. 2  as described above, the transmission gear mechanism  17  is constructed using the single planetary gear unit  17   a . According to this invention, the transmission gear mechanism  17  may also be constructed using a double planetary gear unit.  FIG. 10  shows an example in which the transmission gear mechanism  17  uses such a double planetary gear unit, and the drive train is suitable for installation on an FR-type vehicle. 
     The hybrid vehicle Ve shown in  FIG. 10  is different from the above-described hybrid vehicle Ve shown in  FIG. 1  only in the arrangement of the transmission gear mechanism  17 , and the coupling relationship between the transmission gear mechanism  17 , and the engine  1  and the first motor-generator  2 . More specifically, in the example as shown in  FIG. 10 , the transmission gear mechanism  17  is constituted by a double pinion type planetary gear unit  17   b  having a ring gear  31 , a carrier  32 , and a sun gear  33 . The ring gear  31  is coupled to the output shaft  1   a  of the engine  1 . The carrier  32  is coupled to the carrier  8  of the power split mechanism  4  so as to rotate as a unit with the carrier  8 . The carrier  32  in the example shown in  FIG. 10  holds two pinion gears such that the gears can rotate about themselves and rotate about the axis of the transmission gear mechanism  17 . One of the two pinion gears meshes with the sun gear  33 , and the other pinion gear meshes with the ring gear  31 , while the two pinion gears mesh with each other. The clutch C 1  for selectively coupling the sun gear  33  with the carrier  32  is provided between the sun gear  33  and the carrier  32 . Also, the brake B 1  is provided for selectively fixing the sun gear  33  in a non-rotatable condition. 
     In the transmission gear mechanism  17  in the example shown in  FIG. 10 , too, when the clutch C 1  is engaged, the sun gear  33  and carrier  32  of the planetary gear unit  17   b  are coupled to each other, as in the above-described example shown in  FIG. 1 . As a result, the whole planetary gear unit  17   b  rotates as a unit, and the transmission gear mechanism  17  is placed in a so-called directly connected state in which the mechanism  17  produces no speed-increasing effect nor speed-reducing effect. If the brake B 1  is engaged in addition to the clutch C 1 , the whole transmission gear mechanism  17  is fixed as a unit, and rotation of the carrier  8  of the power split mechanism  4  and the engine  1  is stopped. On the other hand, if only the brake B 1  is engaged, the sun gear  33  becomes a fixed element, and the ring gear  31  becomes an input element, in the transmission gear mechanism  17  in the example shown in  FIG. 10 . Therefore, the carrier  32  that becomes an output element when the ring gear  31  is the input element rotates at a higher speed than the ring gear  31 , in the same direction as the ring gear  31 . Accordingly, the transmission gear mechanism  17  functions as a speed increasing mechanism. Namely, the O/D speed position (High) is established in the transmission gear mechanism  17 . 
       FIG. 11  shows an example in which the transmission gear mechanism  17  is constructed using a double planetary gear unit, and the drive train is suitable for installation on an FF-type vehicle. The hybrid vehicle Ve shown in  FIG. 11  is different from the above-described hybrid vehicle Ve shown in  FIG. 2  only in the arrangement of the transmission gear mechanism  17 , and the coupling relationship between the transmission gear mechanism  17 , and the engine  1  and the first motor-generator  2 . The transmission gear mechanism  17  constituted by the double pinion type planetary gear unit  17   b , and the coupling relationship between the transmission gear mechanism  17 , and the engine  1  and the first motor-generator  2 , are similar to those of the drive train of the hybrid vehicle Ve shown in  FIG. 10 . 
     As described above, the power transmitting apparatus TM for the hybrid vehicle according to this invention includes the transmission gear mechanism  17  provided between the engine  1  and the power split mechanism  4  for changing the rotational speed of the engine  1 . The transmission gear mechanism  17  includes friction devices, i.e., the clutch C 1  and the brake B 1 , for switching the speed position between the directly connected state (Low) and the O/D state (High). The clutch C 1  and brake B 1  of the transmission gear mechanism  17  are controlled by use of hydraulic pressure, as in the known arrangement. Namely, each of the clutch C 1  and the brake B 1  includes a hydraulic actuator for controlling the engaged and released states thereof, as will be described later. 
     Accordingly, in the power transmitting apparatus TM for the hybrid vehicle according to the invention, there is a need to separately provide oil passages for shift control, through which hydraulic pressures are supplied to the hydraulic actuators when the operation of the transmission gear mechanism  17  is controlled, as compared with the known power transmitting apparatus for the hybrid vehicle having no mechanism like the transmission gear mechanism  17 . As the oil passages for shift control, oil passages formed in the interior of a rotary shaft or shafts for supplying lubricating oil to respective parts of devices in the known system may be utilized. However, a larger pressure is applied to the oil passages for shift control, as compared with the oil passages for lubrication; therefore, there is a need to separately provide members or mechanisms, such as seal rings, for dealing with hydraulic leak. If the number of locations where the seal rings are used is increased, for example, the arrangement of the oil passages formed within the rotary shaft(s) becomes complicated, and a dragging loss appearing in sliding portions of the seal rings is increased. 
     The power transmitting apparatus for the hybrid vehicle according to this invention is simplified in construction even when the transmission gear mechanism  17  as described above is added to the arrangement of the known system, and the dragging loss caused by the seal rings, etc., can be reduced. One specific example of the arrangement is illustrated in  FIG. 12 . A power transmitting apparatus TM shown in  FIG. 12  corresponds to the arrangement of the drive train as shown in  FIG. 1  and  FIG. 2 . Namely, in the example of  FIG. 12 , the transmission gear mechanism  17  is constituted by the single pinion type planetary gear unit  17   a.    
     The power transmitting apparatus TM includes the transmission gear mechanism  17 , first motor-generator  2 , and the power split mechanism  4 . The transmission gear mechanism  17 , first motor-generator  2 , and the power split mechanism  4  are arranged in the order of description, in a direction from the side closer to the engine  1  (not shown in  FIG. 12 ), namely, from the front side (the left-hand side in  FIG. 12 ) of the power transmitting apparatus TM. 
     The transmission gear mechanism  17  consists of the single pinion type planetary gear unit  17   a , clutch C 1  and brake B 1 , input shaft  100 , and an output flange  101 . The clutch C 1  includes a friction material  102  for coupling the sun gear  20  and the carrier  18  of the planetary gear unit  17   a  to each other, and a hydraulic actuator  103  and a return spring  104  that operate the friction material  102  so as to bring the clutch C 1  into the engaged or released state. In operation, hydraulic pressure for engaging the clutch C 1  is supplied to the hydraulic actuator  103 , via an oil passage  116  for shift control, which will be described later. Meanwhile, the brake B 1  includes a friction material  105  for fixing the sun gear  20  of the planetary gear unit  17   a  in a non-rotatable condition, and a hydraulic actuator  106  and a return spring  107  that operate the friction material  105  so as to bring the brake B 1  into the engaged or released state. In operation, hydraulic pressure for engaging the brake B 1  is supplied to the hydraulic actuator  106 , via an oil passage  117  for shift control, which will be described later. 
     A front cover  108  is provided for housing the above-described planetary gear unit  17   a , clutch C 1  and brake B 1 , and the input shaft  100 . The front cover  108  covers a portion of the power transmitting apparatus TM which is opposed to the engine  1  in a condition where the assembling of the system TM is completed. In the power transmitting apparatus TM as shown in  FIG. 12 , the planetary gear unit  17   a , clutch C 1  and brake B 1 , input shaft  100 , and the output flange  101  are incorporated inside the front cover  108 . 
     More specifically, the hydraulic actuator  103  and the return spring  104 , and the hydraulic actuator  106  and the return spring  107 , are mounted in a front part of the inside of the front cover  108 , namely, on the side (left-hand side in  FIG. 12 ) closer to the engine  1  that is not shown in  FIG. 12 . The planetary gear unit  17   a  is disposed in the rear (on the right-hand side in  FIG. 12 ) of the hydraulic actuator  103 ,  106  and the return spring  104 ,  107  at the radially inner side of the hydraulic actuator  103 ,  106  and the return spring  104 ,  107 . 
     The input shaft  100  that functions as an input member of the transmission gear mechanism  17  is disposed radially inside of the sun gear  20  of the planetary gear unit  17   a , such that the input shaft  100  is rotatable relative to the sun gear  20 . The input shaft  100  is supported by a needle bearing  109  provided in an inner circumferential portion of a through-hole  108   a  formed in the front cover  108 , and a bush  128  provided in an inner circumferential portion of a countersunk hole formed in an input shaft  125  of the power split mechanism  4  which will be described later. 
     The input shaft  100  is formed with a flange  113  that rotates as a unit with the input shaft  100 , and the carrier  18  of the planetary gear unit  17   a  is coupled to the flange  113  so as to rotate as a unit with the flange  113 . Namely, the input shaft  100  and the carrier  18  are coupled to each other so as to rotate as a unit. A front end portion (on the left-hand side in  FIG. 12 ) of the input shaft  100  protrudes from the through-hole  108   a , so that the input shaft  100  and the output shaft  1   a  of the engine  1  are coupled to each other via a damper mechanism (not shown), or the like. A rear end portion (on the right-hand side in  FIG. 12 ) of the input shaft  100  is supported by the input shaft  125  of the power split mechanism  4  which will be described later. 
     The output flange  101  that functions as an output member of the transmission gear mechanism  17  is disposed radially outside of a rear end portion of the input shaft  100 , in the rear of the above-mentioned flange  113 , such that the output flange  101  can rotate relative to the input shaft  100 . The output flange  101  is supported by a thrust bearing  114  provided between the output flange  101  and the flange  113 , and a thrust bearing  115  provided between the output flange  101  and an MG 1  cover  118  which will be described later. 
     The ring gear  19  of the planetary gear unit  17   a  is coupled to the output flange  101  so as to rotate as a unit with the output flange  101 . Internal splines  101   a  are formed in a rear end portion of the output flange  101 . The internal splines  101   a  serve to couple the output flange  101  with the input shaft  125  of the power split mechanism  4  such that power can be transmitted between the output flange  101  and the input shaft  125 . Namely, external splines  125   a  are formed on a front end portion of the input shaft  125  of the power split mechanism  4 , and the output flange  101  is arranged to be spline-fitted on the input shaft  125 . 
     The friction material  102  of the clutch C 1  is disposed radially outside of the hydraulic actuator  103 , the return spring  104 , and the planetary gear unit  17   a . A part of the friction material  102  is coupled to the sun gear  20  of the planetary gear unit  17   a  so as to rotate as a unit with the sun gear  20 . Another part of the friction material  102  is coupled to the carrier  18  of the planetary gear unit  17   a  so as to rotate as a unit with the carrier  18 . In addition, a friction material  105  of the brake B 1  is disposed radially outside of the clutch C 1 . A part of the friction material  105  is coupled to the sun gear  20  of the planetary gear unit  17   a  so as to rotate as a unit with the sun gear  20 . Another part of the friction material  105  is fixed to the stationary member  16  formed inside the front cover  108 . 
     In the power transmitting apparatus TM for the hybrid vehicle according to this invention, the oil passage  116  for speed control through which engaging hydraulic pressure is supplied to the clutch C 1 , and the oil passage  117  for shift control through which engaging hydraulic pressure is supplied to the brake B 1 , are formed in the front cover  108 . In the example as shown in  FIG. 12 , for example, the oil passage  116  for shift control is a communication hole formed by drilling or boring at three locations in the interior of the front cover  108 . Similarly, the oil passage  117  for shift control is a communication hole formed by drilling or boring at three locations in the interior of the front cover  108 . With the front cover  108  assembled with the MG 1  cover  118  and a housing  122  which will be described later, supply oil passages  122   b  formed in the housing  122  are connected to the oil passage  116  for shift control and the oil passage  117  for shift control, respectively. The hydraulic pressures for controlling the clutch C 1  and the brake B 1  are respectively supplied, from a valve body (not shown) side provided with a hydraulic source, such as an oil pump, to the supply oil passages  122   b.    
     In the power transmitting apparatus TM, oil passages through which the lubricating oil is supplied to the planetary gear unit  17   a , the rotor  2   a  of the first motor-generator  2 , and the power split mechanism  4 , for example, are formed within the respective rotary shafts of the power transmitting apparatus TM. Namely, an oil passage  100   a  for supply of lubricating oil is formed around the center axis of rotation within the input shaft  100  of the transmission gear mechanism  17 . Similarly, an oil passage  125   b  for supply of lubricating oil is formed around the center axis of rotation within the input shaft  125  of the power split mechanism  4 . Similarly, an oil passage  126   a  for supply of lubricating oil is formed around the center axis of rotation within the output shaft  126  of the power split mechanism  4  which will be described later. 
     The oil passage  100   a  formed within the input shaft  100  communicates with an oil passage  100   b  and an oil passage  100   c  which are formed through between the oil passage  100   a  and the outer periphery of the input shaft  100 . The oil passage  100   b  is arranged to allow hydraulic pressure for lubrication to be supplied to a sliding portion between the input shaft  100  and the inner periphery of the front cover  108  and a sleeve  111 . The oil passage  100   c  is arranged to allow hydraulic pressure for lubrication to be supplied to the planetary gear unit  17   a  of the transmission gear mechanism  17 , etc. 
     The oil passage  125   b  formed within the input shaft  125  communicates with an oil passage  125   c , oil passage  125   d , and an oil passage  125   e  which are formed through between the oil passage  125   b  and the outer periphery of the input shaft  125 . The oil passage  125   c  is arranged to allow hydraulic pressure for lubrication to be supplied to a sliding portion between the input shaft  125  and the inner periphery of the rotor  2   a  of the first motor-generator  2 . The oil passage  125   d  is arranged to allow hydraulic pressure for lubrication to be supplied to the planetary gear unit of the power split mechanism  4 , etc. The oil passage  125   e  is arranged to allow hydraulic pressure for lubrication to be supplied to a sliding portion between the input shaft  125  and the inner periphery of a flange  127  of the power split mechanism  4  which will be described later. 
     Thus, the oil passages for allowing supply of the hydraulic pressure for lubrication are formed within the respective rotary shafts of the power transmitting apparatus TM. On the other hand, the oil passages  116 ,  117  for shift control through which the hydraulic pressure for shift control of the transmission gear mechanism  17  are not formed within the respective rotary shafts of the power transmitting apparatus TM, but formed in the interior of the front cover  108  as described above. Accordingly, in the power transmitting apparatus TM of this invention, the oil passages formed within the rotary shafts are exclusively used for hydraulic oil for lubrication having a lower pressure that of the hydraulic oil for shift control. As a result, the arrangement of the oil passages within the rotary shafts, and the oil passages through which the lubricating oil is supplied from within the rotary shafts to respective parts of the system is simplified, as compared with the arrangement in which the oil passages that allow supply of the hydraulic pressure for shift control are provided within the rotary shafts. For example, the strength of seal rings (not shown) used for preventing hydraulic leak is reduced, or the number of locations where the seal rings are used is reduced. As the oil passages for shift control are not provided in the rotary shafts, the number of locations where the seal rings are used is surely reduced. Therefore, the dragging loss that appears at sliding portions of the seal ring during rotation of the rotary shafts can be reduced. 
     The constituent members, such as the planetary gear unit  17   a , clutch C 1 , brake B 1 , and the input shaft  100 , of the transmission gear mechanism  17  are housed and mounted inside the front cover  108 . With these members constituting the transmission gear mechanism  17  thus mounted in position, the MG 1  cover  118  is mounted to a rear opening portion of the front cover  108 . For example, as shown in  FIG. 12 , the front cover  108  and the MG 1  cover  118  are fixed integrally, by means of a plurality of bolts  119 . The MG 1  cover  118  is formed with a through-hole  118   a  similar to the through-hole  108   a  of the front cover  108 . The input shaft  100  of the transmission gear mechanism  17  and the input shaft  125  of the power split mechanism  4  (which will be described later) are connected in the through-hole  118   a  such that the input shafts  100 ,  125  can rotate relative to each other. Also, the output flange  101  of the transmission gear mechanism  17  is arranged to be spline-fitted on the input shaft  125  of the power split mechanism  4 . 
     The MG 1  cover  118  as described above is formed along the shape of a front end portion (on the left-hand side in  FIG. 12 ) of the first motor-generator  2 . Therefore, a radially outer portion of the MGI cover  118  is formed in accordance with the position of a front end portion of a coil end  2   b  of the first motor-generator  2 , whereas a central portion of the MG 1  cover  118  in which the through-hole  118   a  is formed is shaped to be located radially inside of the coil end  2   b  and a stator  2   c . Namely, as shown in the cross-sectional view of  FIG. 12 , the central portion of the MG 1  cover  118  is shaped so as to protrude rightward in  FIG. 12 , so that the through-hole  118   a  is located in a radially inner portion of the first motor-generator  2 . Accordingly, the output flange  101  of the transmission gear mechanism  17  and the input shaft  125  of the power split mechanism  4  are coupled to each other via splines, in the radially inner portion of the first motor-generator  2 . 
     Thus, in the power transmitting apparatus TM according to this invention, the space in the radially inner portion of the first motor-generator  2  is effectively utilized for placement of the transmission gear mechanism  17  and the power split mechanism  4  as described above. Therefore, the overall length of the power transmitting apparatus TM as measured in the direction of its rotational axis can be shortened, and the size and weight of the power transmitting apparatus TM can be reduced. 
     In the example as shown in  FIG. 12 , space  108   b  is formed between the outer periphery of the stationary member  16  to which the friction material  105  of the brake B 1  is fixed, and the inner periphery of the front cover  108 . This space  108   b  effectively functions as an oil return or oil reservoir for oil supplied to the transmission gear mechanism  17 . 
     A ball bearing  120  for supporting a front end portion (on the left-hand side in  FIG. 12 ) of the rotor  2   a  of the first motor-generator  2  is mounted on a rear-side (the right-hand side in  FIG. 12 ) surface of the MG 1  cover  118 . More specifically, an outer race  120   a  of the ball bearing  120  is fixed to the MG 1  cover  118 . Then, the MG 1  cover  118  fixed integrally with the front cover  108  is mounted to the housing  122  in which the first motor-generator  2  (which will be described later) is housed, so that the rotor  2   a  is assembled with the inner race  120   b  of the ball bearing  120 . Also, a rear end portion (on the right-hand side in  FIG. 12 ) of the rotor  2   a  is supported by a ball bearing  124  which will be described later. 
     As described above, the transmission gear mechanism  17  is formed as one unit in a condition where the respective members, such as the planetary gear unit  17   a , clutch C 1 , brake B 1  and the input shaft  100 , which constitute the transmission gear mechanism  17  are incorporated inside the front cover  108 , and covered with the MG 1  cover  118  as a lid. Namely, the transmission gear mechanism  17  of this invention can be formed as a transmission gear unit covered with the front cover  108  and the MG 1  cover  118 , and the transmission gear unit can be handled as a sub-assembly. 
     The housing  122  in which the first motor-generator  2 , a resolver  121 , etc. are housed is disposed in the rear of the front cover  10  and MG cover  118  in which the transmission gear mechanism  17  is housed. Namely, the front cover  108  and MG 1  cover  118  which house the transmission gear mechanism  17  therein to form the transmission gear unit as described above are fixed to the front (the left-hand side in  FIG. 12 ) of the housing  122 . For example, the front cover  108  and the MG 1  cover  118  are fixed integrally with the housing  122 , by means of a plurality of bolts  123 , as shown in  FIG. 12 . 
     The housing  122  is open frontward, namely, toward the MG 1  cover  118  (on the left-hand side in  FIG. 12 ), and the resolver  121  is mounted on the inner side of a rear side wall portion  122   a  of the housing  122 . A through-hole is formed in the side wall portion  122   a , and the ball bearing  124  is mounted in an inner circumferential portion of the through-hole. The stator  2   c  of the first motor-generator  2  is fixed inside the housing  122  in front of the resolver  121 . 
     The rotor  2   a  of the first motor-generator  2  is inserted in a radially inner portion of the stator  2   c . With the housing  122  assembled integrally with the front cover  108  and the MG 1  cover  118 , the front end portion (on left-hand side in  FIG. 12 ) of the rotor  2   a  is supported by the MG 1  cover  118  via the ball bearing  120 , as described above. On the other hand, the rear end portion (on the right-hand side in  FIG. 12 ) of the rotor  2   a  is supported by the housing  122  via the ball bearing  124 . Internal splines  2   d  are formed in the rear end portion of the rotor  2   a . The internal splines  2   d  are used for coupling the rotor  2   a  with the sun gear  6  of the power split mechanism  4  such that dynamic power can be transmitted therebetween. Namely, external splines  127   a  are formed on a flange  127  coupled integrally with the sun gear  6  of the power split mechanism  4  as described later, and the rotor  2   a  is spline-fitted on the flange  127 . 
     The power split mechanism  4  is disposed inside the housing  122  in which the first motor-generator  2  is housed. The power split mechanism  4  is constituted by the single pinion type planetary gear unit as described above, and includes the input shaft  125  to which the carrier  8  is coupled so as to rotate as a unit with the input shaft  125 , and the output shaft  126  to which the ring gear  7  is coupled so as to rotate as a unit with the output shaft  126 . The flange  127  is coupled to the sun gear  6  of the power split mechanism  4  so as to rotate as a unit with the sun gear  6 . The external splines  127   a  are formed on the outer periphery of the front end portion (on the left-hand side in  FIG. 12 ) of the flange  127 . The flange  127 , and the rotor  2   a  of the first motor-generator  2  formed with the internal splines  2   d  are arranged to be spline-fitted on each other. Namely, the sun gear  6  of the power split mechanism  4  is splined to the rotor  2   a  of the first motor-generator  2  so that the sun gear  6  and the rotor  2   a  rotate as a unit. 
     The input shaft  125  is inserted in radially inner portions of the sun gear  6  and the flange  127 , such that the sun gear  6  of the power split mechanism  4  and the flange  127  can rotate relative to each other. A front portion (on the left-hand side in  FIG. 12 ) of the input shaft  125  protrudes from the flange  127 , and the portion of the input shaft  125  protruding from the flange  127  is inserted through a radially inner portion of the rotor  2   a  so as to be rotatable relative to the rotor  2   a . Also, the external splines  125   a  are formed on the outer periphery of the front end portion of the input shaft  125 . Thus, the input shaft  125 , and the output flange  101  of the transmission gear mechanism  17  formed with the internal splines  101   a , are spline-fitted on each other. Namely, the output flange  101  as the output member of the transmission gear mechanism  17  and the input shaft  125  as the input member of the power split mechanism  4  are splined to each other so as to rotate as a unit. In this connection, serration, rather than splines, may be used for coupling the output flange  101  with the input shaft  125 . 
     Furthermore, the countersunk hole is formed in a front end portion of the input shaft  125 . The countersunk hole is used for supporting a rear end portion (on the right-hand side in  FIG. 12 ) of the input shaft  100  of the transmission gear mechanism  17  so that the input shaft  100  and the input shaft  125  can rotate relative to each other. The bush  128  is provided between the rear end portion of the input shaft  100  and the countersunk hole formed in the front end portion of the input shaft  125 . 
     A flange  129  that rotates as a unit with the output shaft  126  is formed on a front end portion (on the left-hand side in  FIG. 12 ) of the output shaft  126 , and the ring gear  7  of the power split mechanism  4  is coupled to the flange  129  so as to rotate as a unit with the flange  129 . Namely, the output shaft  126  and the ring gear  7  are coupled to each other so as to rotate as a unit. On the other hand, a rear end portion (on the right-hand side in  FIG. 12 ) of the output shaft  126  is coupled to the propeller shaft  9  which is not illustrated in  FIG. 12  so as to rotate as a unit with the propeller shaft  9 . The rear portion of the output shaft  126  is supported by a rear cover  130  mounted on the rear side of the housing  122 . Namely, a through-hole is formed in a front side wall portion  130   a  of the rear cover  130 , and the rear portion of the output shaft  126  is inserted in the through-hole of the side wall portion  130   a . Thus, the output shaft  126  is supported by the inner circumferential wall of the through-hole of the side wall portion  130   a.    
     Furthermore, a countersunk hole is formed in the front end portion of the output shaft  126 . The countersunk hole is used for supporting a rear end portion (on the right-hand side in  FIG. 12 ) of the input shaft  125  of the power split mechanism  4  such that the input shaft  125  and the output shaft  126  are rotatable relative to each other. A bush  131  is provided between the rear end portion of the input shaft  125 , and the countersunk hole formed in the front end portion of the output shaft  126 . 
     In the example as described above, the ring gear  7  of the power split mechanism  4  is coupled to the propeller shaft  9  via the output shaft  126 , namely, the power transmitting apparatus TM of this invention is used in the drive train suitable for installation on the FR-type vehicle as shown in  FIG. 1 . On the other hand, if the power transmitting apparatus TM of this invention is used in the drive train suitable for installation on the FF-type vehicle as shown in  FIG. 2 , the ring gear  7  of the power split mechanism  4  is coupled to the drive gear  25  that constitutes the gear train  12 , via the output shaft  126 , so as to rotate as a unit with the drive gear  25 . The other portions of the power transmitting apparatus TM are constructed similarly to those of the example as shown in  FIG. 12 . 
       FIG. 13  shows another example of power transmitting apparatus according to this invention. The power transmitting apparatus TM shown in  FIG. 13  corresponds to the arrangement of the drive trains as shown in  FIG. 10  and  FIG. 11 . Namely, the transmission gear mechanism  17  is constituted by the double pinion type planetary gear unit  17   b.    
     In  FIG. 13 , the power transmitting apparatus TM includes the transmission gear mechanism  17 , first motor-generator  2 , and the power split mechanism  4 , as in the arrangement shown in  FIG. 12 . The transmission gear mechanism  17 , first motor-generator  2 , and the power split mechanism  4  are arranged in the order of description, as viewed from the side closer to the engine  1  (not shown in  FIG. 13 ), namely, as viewed from the front side (the left-hand side in  FIG. 13 ) of the power transmitting apparatus TM. 
     In the arrangement shown in  FIG. 13 , the transmission gear mechanism  17  consists of the double pinion type planetary gear unit  17   b , clutch C 1  and brake B 1 , input shaft  200 , and an intermediate shaft  201 . The clutch C 1  includes a friction material  202  for coupling the sun gear  33  and the carrier  32  of the planetary gear unit  17   b , and a hydraulic actuator  203  and a return spring  204  that operate the friction material  202  so as to bring the clutch C 1  into the engaged or released state. In operation, hydraulic pressure for engaging the clutch C 1  is supplied to the hydraulic actuator  203 , via an oil passage  218  for shift control, which will be described later. On the other hand, the brake B 1  includes a friction material  205  for fixing the sun gear  33  of the planetary gear unit  17   b  in a non-rotatable condition, and a hydraulic actuator  206  and a return spring  207  that operate the friction material  205  so as to bring the brake B 1  into the engaged or released state. In operation, hydraulic pressure for engaging the brake B 1  is supplied to the hydraulic actuator  206 , via an oil passage  219  for shift control, which will be described later. 
     A front cover  208  is provided for housing the above-described planetary gear unit  17   b , clutch C 1  and brake B 1 , and the input shaft  200 . The front cover  208  covers a portion of the power transmitting apparatus TM which is opposed to the engine  1  in a condition where the assembling of the system TM is completed. In the power transmitting apparatus TM shown in  FIG. 13 , the planetary gear unit  17   b , clutch C 1  and brake B 1 , input shaft  200 , and the intermediate shaft  201  are incorporated inside the front cover  208 . 
     More specifically, the planetary gear unit  17   b  is mounted in a front part of the inside of the front cover  208 , namely, on the side (the left-hand side in  FIG. 13 ) closer to the engine  1  that is not shown in  FIG. 13 . The input shaft  200  that functions as an input member of the transmission gear mechanism  17  is disposed radially inside of the sun gear  33  of the planetary gear unit  17   b , such that the input shaft  200  is rotatable relative to the sun gear  33  and the intermediate shaft  201 . The input shaft  200  is supported by a needle bearing  209  provided in an inner circumferential portion of a through-hole  208   a  formed in the front cover  208 , and a bush  210  provided in an inner circumferential portion of the intermediate shaft  201  which will be described later. The hydraulic actuator  203  and the return spring  204 , and the hydraulic actuator  206  and the return spring  207 , are mounted at the rear (the right-hand side in  FIG. 12 ) of the planetary gear unit  17   b.    
     The input shaft  200  is formed with a flange  211  that rotates as a unit with the input shaft  200 , and the ring gear  31  of the planetary gear unit  17   b  is coupled to the flange  211  so as to rotate as a unit with the flange  211 . Namely, the input shaft  200  and the ring gear  31  are coupled to each other so as to rotate as a unit. A front end portion (on the left-hand side in  FIG. 13 ) of the input shaft  200  protrudes from the through-hole  208   a , so that the input shaft  200  and the output shaft  1   a  of the engine  1  are coupled to each other via a damper mechanism (not shown), or the like. A rear end portion (on the right-hand side in  FIG. 13 ) of the input shaft  200  is supported by the intermediate shaft  201  as will be described later. A portion of the input shaft  200  located at the rear of the flange  211  has a smaller outside diameter than the other portion, so that it can be inserted into a countersunk hole formed in the intermediate shaft  201 . 
     The intermediate shaft  201  that functions as an output member of the transmission gear mechanism  17 , in addition to the input shaft  200 , is disposed radially inside of the sun gear  33  of the planetary gear unit  17   b , such that the intermediate shaft  201  is rotatable relative to the input shaft  200  and the sun gear  33 . Also, the intermediate shaft  201  is located on the rear side of the input shaft  200 , on the same rotational axis as the input shaft  200 . The intermediate shaft  201  is supported by a needle bearing  215  provided in an inner circumferential portion of a through-hole  217   a  formed in an MG 1  cover  217  which will be described later, and a needle bearing  216  provided on the inner periphery of the rotor  2   a  of the first motor-generator  2 . 
     The carrier  32  of the planetary gear unit  17   b  is coupled to the intermediate shaft  201  so as to rotate as a unit with the shaft  201 . Also, a countersunk hole for supporting the rear small-diameter portion of the input shaft  200  is formed in a front end portion of the intermediate shaft  201 , such that the input shaft  200  and the intermediate shaft  201  can rotate relative to each other. The bush  210  is provided between the rear end portion of the input shaft  200 , and the countersunk hole formed in the front end portion of the intermediate shaft  201 . Internal splines  201   a  are formed in a rear end portion of the intermediate shaft  201 . The internal splines  201   a  are used for coupling the intermediate shaft  201  with the input shaft  125  of the power split mechanism  4  such that dynamic power can be transmitted therebetween. Namely, external splines  125   a  are formed on a front end portion of the input shaft  125  of the power split mechanism  4 , and the intermediate shaft  201  and the input shaft  125  are spline-fitted on each other. Accordingly, the intermediate shaft  201  as the output member of the transmission gear mechanism  17  and the input shaft  125  as the input member of the power split mechanism  4  are splined to each other so as to rotate as a unit. In this connection, serration, rather than splines, may be used for coupling the intermediate shaft  201  with the input shaft  125 . 
     The friction material  202  of the clutch C 1  is disposed radially outside of the hydraulic actuator  203  and the return spring  204 , and the planetary gear unit  17   b . A part of the friction material  202  is coupled to the sun gear  33  of the planetary gear unit  17   b  so as to rotate as a unit with the sun gear  33 . Another part of the friction material  202  is coupled to the carrier  32  of the planetary gear unit  17   b  so as to rotate as a unit with the carrier  32 . Furthermore, a friction material  205  of the brake B 1  is disposed radially outside of the clutch C 1 . A part of the friction material  205  is fixed to the stationary member  16  formed inside the MG 1  cover  217 . 
     The constituent members, such as the planetary gear unit  17   b , clutch C 1 , brake B 1 , input shaft  200 , and the intermediate shaft  201 , of the transmission gear mechanism  17  are housed and mounted within the front cover  208 . With these members constituting the transmission gear mechanism  17  thus mounted in position, the MG 1  cover  217  is mounted to a rear opening portion of the front cover  208 . For example, as shown in  FIG. 13 , the front cover  208  and the MG 1  cover  217  are fixed integrally to each other, by means of a plurality of bolts  119 . The MG 1  cover  217  is formed with a through-hole  217   a  similar to the through-hole  208   a  of the front cover  208 . The intermediate shaft  201  is inserted in the through-hole  217   a . The rear end portion of the intermediate shaft  201  which is formed with the internal splines  201   a  protrudes rearward from the through-hole  217   a , so as to be spline-fitted on the input shaft  125  of the power split mechanism  4 , in a radially inner portion of the rotor  2   a  of the first motor-generator  2 . 
     The MG 1  cover  217  as described above is formed along the shape of a front end portion (on the left-hand side in  FIG. 12 ) of the first motor-generator  2 . Therefore, a radially outer portion of the MG 1  cover  217  is formed in accordance with the position of a front end portion of a coil end  2   b  of the first motor-generator  2 , whereas a central portion of the MG 1  cover  217  in which the through-hole  217   a  is formed is shaped to be located radially inside of the coil end  2   b  and a stator  2   c . Namely, as shown in the cross-sectional view of  FIG. 13 , the central portion of the MG 1  cover  217  is shaped so as to protrude rightward in  FIG. 13 , so that the through-hole  217   a  is located in a radially inner portion of the first motor-generator  2 . Accordingly, the intermediate shaft  201  of the transmission gear mechanism  17  and the input shaft  125  of the power split mechanism  4  are coupled to each other via splines, in the radially inner portion of the first motor-generator  2 . 
     In the example shown in  FIG. 13 , too, in the power transmitting apparatus TM according to this invention, the space in the radially inner portion of the first motor-generator  2  is effectively utilized for placement of the transmission gear mechanism  17  and the power split mechanism  4 , as in the above-described example shown in  FIG. 12 . Therefore, the overall length of the power transmitting apparatus TM as measured in the direction of its rotational axis can be shortened, and the size and weight of the power transmitting apparatus TM can be reduced. 
     In the power transmitting apparatus TM for the hybrid vehicle according to this invention as shown in  FIG. 13 , the oil passage  218  for shift control through which engaging hydraulic pressure is supplied to the clutch C 1 , and the oil passage  219  for shift control through which engaging hydraulic pressure is supplied to the brake B 1 , are formed in the MG 1  cover  217 . The oil passage  218  for shift control is formed by fixing a tubular member formed in a given shape in accordance with the shape of the MG 1  cover  217 , to an inner side surface (on the left-hand side in  FIG. 13 ) of the MG 1  cover  217 , or holding the tubular member thereon. The oil passage  218  for shift control may be formed by subjecting a pipe made of a metal to a bending process for plastic deformation of the pipe. On the other hand, the oil passage  219  for shift control is a communication hole formed by boring or drilling at three locations within the front cover  208 . With the front cover  208  assembled with the MG 1  cover  217  and the housing  122 , supply oil passages  122   b  formed in the housing  122  are connected to the oil passage  218  for shift control and the oil passage  219  for shift control, respectively. Hydraulic pressures for controlling the clutch C 1  and the brake B 1  are respectively supplied, from a valve body (not shown) side provided with a hydraulic source, such as an oil pump, to the supply oil passages  122   b.    
     In the power transmitting apparatus TM as shown in FIG,  13 , too, oil passages through which the lubricating oil is supplied to the planetary gear unit  17   b , the rotor  2   a  of the first motor-generator  2 , and the power split mechanism  4 , for example, are formed within the respective rotary shafts of the power transmitting apparatus TM. Namely, an oil passage  200   a  for use in supply of lubricating oil is formed around the center axis of rotation of the input shaft  200  of the transmission gear mechanism  17 . Similarly, an oil passage  201   b  for use in supply of lubricating oil is formed around the center axis of rotation of the intermediate shaft  201  of the transmission gear mechanism  17 . Similarly, an oil passage  125   b  for use in supply of lubricating oil is formed around the center axis of rotation of the input shaft  125  of the power split mechanism  4 . Similarly, an oil passage  126   a  for use in supply of lubricating oil is formed around the center axis of rotation of the output shaft  126  of the power split mechanism  4 . 
     The oil passage  200   a  formed within the input shaft  200  communicates with an oil passage  200   b  and an oil passage  200   c  which are formed through between the oil passage  200   a  and the outer periphery of the input shaft  200 . The oil passage  200   b  is arranged to allow hydraulic pressure for lubrication to be supplied to a sliding portion between the input shaft  200  and the front cover  108 . The oil passage  200   c  is arranged to allow hydraulic pressure for lubrication to be supplied to a sliding portion between the input shaft  200  and the inner periphery of the intermediate shaft  201  that supports the input shaft  200 . 
     The oil passage  201   b  formed within the intermediate shaft  201  communicates with an oil passage  201   c  and an oil passage  201   d  which are formed through between the oil passage  201   b  and the outer periphery of the intermediate shaft  201 . The oil passage  201   c  is arranged to allow hydraulic pressure for lubrication to be supplied to the planetary gear unit  17   b  of the transmission gear mechanism  17 , etc. The oil passage  201   d  is arranged to allow hydraulic pressure for lubrication to be supplied to sliding portions between the intermediate shaft  201 , and the inner peripheries of the MG 1  cover  217  and the rotor  2   a  of the first motor-generator  2 . 
     The oil passage  125   b  formed within the input shaft  125  communicates with an oil passage  125   d  and an oil passage  125   e  which are formed through between the oil passage  125   b  and the outer periphery of the input shaft  125 . The oil passage  125   d  is arranged to allow hydraulic pressure for lubrication to be supplied to the planetary gear unit of the power split mechanism  4 , etc. The oil passage  125   e  is arranged to allow hydraulic pressure for lubrication to be supplied to a sliding portion between the input shaft  125  and the inner periphery of a flange  127  of the power split mechanism  4  which will be described later. 
     Thus, in the power transmitting apparatus TM as shown in  FIG. 13 , too, the oil passages used for supplying the hydraulic pressure for lubrication are formed within the respective rotary shafts of the power transmitting apparatus TM. On the other hand, the oil passages  218 ,  219  for shift control used for supplying the hydraulic pressure for shift control of the transmission gear mechanism  17  are not formed within the respective rotary shafts of the power transmitting apparatus TM, but formed along the MG 1  cover  217  or formed in the interior of the MG 1  cover  217  as described above. Accordingly, in the power transmitting apparatus TM of this invention, the oil passages formed within the rotary shafts are exclusively used for hydraulic oil for lubrication having a lower pressure than the hydraulic pressure for shift control. Therefore, the arrangement of the oil passages within the rotary shafts, the oil passages through which the lubricating oil is supplied from within the rotary shafts to respective parts of the system, etc., is simplified, as compared with the arrangement in which the oil passages used for supplying the hydraulic pressure for shift control are provided within the rotary shafts. For example, the strength of seal rings (not shown) used for preventing hydraulic leak is reduced, or the number of locations where the seal rings are used is reduced. As the oil passages for shift control are not provided in the rotary shafts, the number of locations where the seal rings are used is surely reduced. 
     A ball bearing  120  for supporting a front end portion (on the left-hand side in  FIG. 13 ) of the rotor  2   a  of the first motor-generator  2  is mounted on a rear side face (on the right-hand side in  FIG. 13 ) of the MG 1  cover  217 . More specifically, an outer race  120   a  of the ball bearing  120  is fixed to the MG 1  cover  217 . When the MG 1  cover  217  fixed integrally with the front cover  208  is mounted to the housing  122  in which the first motor-generator  2  is housed, a part of the rotor  2   a  is embedded in an inner race  120   b  of the ball bearing  120 . 
     As described above, the transmission gear mechanism  17  is formed as one unit in a condition where the respective members, such as the planetary gear unit  17   b , clutch C 1 , brake B 1 , input shaft  200  and the intermediate shaft  201 , which constitute the transmission gear mechanism  17  are incorporated inside the front cover  208 , and covered with the MG 1  cover  217  as a lid. Namely, the transmission gear mechanism  17  of this invention can be formed as a transmission gear unit covered with the front cover  208  and the MG 1  cover  217 , and the transmission gear unit can be handled as a sub-assembly. 
     The housing  122  in which the first motor-generator  2 , resolver  121 , etc. are housed is disposed in the rear of the front cover  208  and MG 1  cover  217  in which the transmission gear mechanism  17  is housed. Namely, the front cover  208  and MG 1  cover  217  in which the transmission gear mechanism  17  is housed to provide the transmission gear unit as described above are fixed to the front (the left-hand side in  FIG. 12 ) of the housing  122 . For example, the front cover  208  and the MGI cover  217  are fixed integrally with the housing  122 , by means of a plurality of bolts  123 , as shown in  FIG. 13 . The arrangement in the rear of the front cover  208  and the MG 1  cover  217 , namely, the arrangement that extends rearwards from the housing  122 , is substantially the same as the arrangement shown in  FIG. 12 . 
     The procedure of assembling the power transmitting apparatus TM as shown in  FIG. 12  or  FIG. 13  will be described. Initially, the ball bearing  124  and the resolver  121  are mounted inside the housing  122 . Then, the stator  2   c  of the first motor-generator  2  is mounted in position. Then, the rotor  2   a  of the first motor-generator  2  is built in a radially inner portion of the stator  2   c.    
     Separately from assembling of the resolver  121  and the first motor-generator  2  with the housing  122  as described above, the transmission gear unit is assembled. Namely, the clutch C 1  and the brake B 1  are mounted inside the front cover  108 . Then, the planetary gear unit  17   a , the input shaft  100 , and the output flange  101  are mounted in position. Then, the MG 1  cover  118  is mounted to the front cover  108  such that the front cover  108  is lid by the MG 1  cover  118 . In the example of  FIG. 13 , the planetary gear unit  17   b , the input shaft  200 , and the intermediate shaft  201  are mounted inside the front cover  208 . Then, the clutch C 1  and the brake B 1  are mounted in position. Then, the MGI cover  217  is mounted to the front cover  208  such that the front cover  208  is lid by the MG 1  cover  217 . In this manner, the transmission gear mechanism  17 , which is covered with the front cover  208  and the MG 1  cover  217 , is assembled as the transmission gear unit. 
     The transmission gear unit, namely, the transmission gear mechanism  17  mounted inside the front cover  108  and the MG 1  cover  118  or inside the front cover  208  and the MG 1  cover  217 , is mounted to the housing  122  in which the resolver  121 , the first motor-generator  2 , etc. are incorporated. Namely, the transmission gear unit incorporating the transmission gear mechanism  17  is mounted on the left-hand side of the housing  122  as viewed in  FIG. 12  or  FIG. 13 . 
     As described above, in the power transmitting apparatus TM according to this invention, the transmission gear unit is mounted to the housing  122 , so that the oil passages  116 ,  117  for shift control, or the oil passages  218 ,  219  for shift control, are connected to the supply oil passage  122   b  formed in the housing  122 . Accordingly, with the transmission gear unit incorporating the transmission gear mechanism  17  thus mounted to the housing  122  as described above, the oil passages  116 ,  117  for shift control, or the oil passages  218 ,  219  for shift control, are brought into communication with the supply oil passage  122   b  of the housing  122 , and the hydraulic pressure for shift control, which is supplied from a hydraulic source, can be supplied to the hydraulic actuators  103 ,  106  or the hydraulic actuators  203 ,  206  of the transmission gear mechanism  17 , through the supply oil passage  122   b , and the oil passages  116 ,  117  for shift control or the oil passages  218 ,  219  for shift control. 
     In the condition where the transmission gear unit is mounted to the housing  122  as described above, an inspection of the first motor-generator  2  can be conducted. More specifically, a dummy shaft (not shown) on which external splines similar to the external splines  127   a  are formed is used in place of the flange  127  of the power split mechanism  4  on which the external splines  127   a  are formed, and the dummy shaft is fitted in the internal splines  2   d  formed in the rear end portion (on the right-hand side in  FIG. 12  and  FIG. 13 ) of the rotor  2   a  of the first motor-generator  2 . Then, the dummy shaft is connected to a certain measurement instrument, and the first motor-generator  2  is test-driven, so that the operation of the first motor-generator  2  can be easily checked, and the resolver  121 , etc. can be easily adjusted. 
     Subsequently, the power split mechanism  4  is mounted to the housing  122  to which the transmission gear unit is mounted. More specifically, the power split mechanism  4  is mounted from the right-hand side (in  FIG. 12  or  FIG. 13 ) of the housing  122 . The power split mechanism  4  is assembled in advance, by mounting the input shaft  125 , flange  127 , output shaft  126 , etc. on the planetary gear unit. The input shaft  125  of the power split mechanism  4  is inserted into the radially inner portion of the rotor  2   a  of the first motor-generator  2  mounted in the housing  122 . Then, the external splines  125   a  formed on the input shaft  125  and the internal splines  101   a  formed in the output flange  101  of the transmission gear mechanism  17  are splined to each other. In the example shown in  FIG. 13 , the external splines  125   a  formed on the input shaft  125  and the internal splines  201   a  formed in the intermediate shaft  201  of the transmission gear mechanism  17  are splined to each other. Namely, the output member of the transmission gear mechanism  17  and the input member of the power split mechanism  4  are coupled to each other via splines. 
     Then, the rear cover  130  is mounted to a rear end portion of the housing  122 . With the rear cover  130  thus mounted to the housing  122 , the output shaft  126  of the power split mechanism  4  is supported, and assembling of the power transmitting apparatus TM is completed. 
     As described above, in the power transmitting apparatus TM according to this invention, the transmission gear mechanism  17  that changes the rotational speed of the engine  1  by hydraulically controlling the clutch C 1  and the brake B 1  is provided between the engine  1  and the power split mechanism  4 . The transmission gear mechanism  17  is formed as an integral transmission gear unit that is housed inside the front cover  108  and the MG 1  cover  118 , or inside the front cover  208  and the MG 1  cover  217 , relative to the housing  122  as a principal part of the power transmitting apparatus TM in which the power split mechanism  4  and the first motor-generator  2  are housed. Accordingly, the transmission gear mechanism  17  including the clutch C 1  and the brake B 1  can be handled as a sub-assembly. 
     In the power transmitting apparatus TM according to this invention, the oil passages  116 ,  117  used for supplying hydraulic pressure to the hydraulic actuators  103 ,  106  for hydraulic control of the transmission gear mechanism  17  are provided by communication holes formed by boring or drilling in the interior of the front cover  108 , for example. In the example shown in  FIG. 13 , the oil passage  219  is provided by a communication hole formed by boring or drilling in the interior of the MG 1  cover  217 . In the same example, the oil passage  218  is formed in a metal pipe formed by bending along the shape of the MG 1  cover  217 . The above-described oil passages  116 ,  117 ,  218 ,  219  are arranged to communicate with the supply oil passage  122   b  formed in the housing  122 , no matter how each oil passage is formed, in a condition where the transmission gear unit including the transmission gear mechanism  17  is mounted to the housing  122 . Therefore, the hydraulic pressure for shift control is supplied to the transmission gear mechanism  17 , via the supply oil passage  122   b  of the housing  122 , and the oil passages  116 ,  117  for shift control or the oil passages  218 ,  219  for shift control. 
     Thus, in the power transmitting apparatus TM according to the invention, the oil passages  116 ,  117 ,  218 ,  219  for shift control through which the hydraulic pressure for shift control is supplied are not formed within the rotary shafts of the power transmitting apparatus TM, but formed in the front cover  108  or the MG 1  cover  217 . Therefore, the oil passages formed within the rotary shafts as in the known system may be used exclusively for hydraulic oil for lubrication having a lower pressure than the control hydraulic pressure. Consequently, the arrangement of the oil passages formed within the rotary shafts can be simplified. Also, since the oil passages  116 ,  117 ,  218 ,  219  for shift control are formed in the front cover  108  or the MG 1  cover  217 , the number of locations where seal rings are used can be reduced. Therefore, the dragging loss that would appear in sliding portions of the seal rings during rotation of the rotary shafts can be reduced. Consequently, the energy efficiency of the power transmitting apparatus TM can be improved. 
     In the above-described specific examples, the so-called two-motor-type hybrid vehicle, which includes the engine  1 , and the first motor-generator  2  and second motor-generator  3 , as sources of driving force has been described as the hybrid vehicle to which the invention is applied. However, the hybrid vehicle of the invention may include an engine, and three or more motor-generators. The hybrid vehicle of the invention may also be a plug-in hybrid vehicle having a battery that can be charged directly from an external power supply.