Abstract:
A first ring gear of a drive unit is connected to a second carrier and is mechanically connected to a counter shaft. A first sun gear is connected to a second sun gear and a first rotary electric machine. A first clutch selectively switches between a connection state and a disconnection state of the first sun gear and an engine. A second clutch selectively switches between a connection state and a disconnection state of a first carrier and the engine. A brake selectively switches between a fixed state and a release state of a second ring gear to and from a fixing member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2016-091019 filed on Apr. 28, 2016 which is incorporated herein by reference in its entirety including the specification, drawings and abstract. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a drive unit. 
     2. Description of Related Art 
     Various proposals have conventionally been made for a drive unit of a vehicle including a rotary electric machine, an engine, and a planetary gear drive. 
     For example, the drive unit disclosed in Japanese Patent Application Publication No. 2006-77857 includes an engine, a first rotary electric machine, a second rotary electric machine, a first planetary gear drive, a second planetary gear drive, a third planetary gear drive, a plurality of clutches, and a brake. 
     In the drive unit, a plurality of travel modes can be set by switching the clutches and the brake. 
     SUMMARY 
     However, when a high driving force is requested, the drive unit disclosed in JP2006-77857A is unable to generate maximum driving force through effective use of all the motive power of two rotary electric machines and the engine. 
     The present disclosure relates to a drive unit in which a plurality of travel modes can be selected, the drive unit having a mechanism capable of generating maximum driving force with use of all the motive power of two rotary electric machines and the engine, when a high driving force is requested. 
     An example aspect of the present disclosure is a drive unit. The drive unit includes a driving shaft connected to driving wheels, an engine, a first rotary electric machine, a second rotary electric machine mechanically connected to the driving shaft, a first planetary gear drive including a first ring gear, a first pinion gear, a first carrier connected to the first pinion gear, and a first sun gear, a second planetary gear drive including a second ring gear, a second pinion gear, a second carrier connected to the second pinion gear, and a second sun gear, a first clutch, a second clutch and a brake. 
     The first ring gear is connected to the second carrier, the first ring gear is mechanically connected to the driving shaft, the first sun gear being connected to the second sun gear and the first rotary electric machine, the first clutch is configured to selectively switch a connection state of the first sun gear and the engine between a connected state and a disconnected state, 
     the second clutch being configured to selectively switch a connection state of the first carrier and the engine between a connected state and a disconnected state, and 
     the brake being configured to selectively switch a fixation state of the second ring gear and a fixing member between a fixed state and a released state. 
     The aforementioned drive unit can generate a high driving force using the motive power of the two rotary electric machines and the engine, when the high driving force is requested. 
     The drive unit in which a plurality of travel modes can be selected can generate the high driving force by combining the motive power of the two rotary electric machines and the engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a schematic view illustrating the overall configuration of a vehicle according to the present embodiment; 
         FIG. 2  is a block diagram illustrating the configuration of a control unit illustrated in  FIG. 1 ; 
         FIG. 3  is an alignment chart in an MG 2  single travel mode; 
         FIG. 4  is an alignment chart in a dual-motor travel mode; 
         FIG. 5  is an alignment chart in a series travel mode; 
         FIG. 6  is an alignment chart in a series parallel travel mode; 
         FIG. 7  is an alignment chart in a parallel travel mode (first speed); 
         FIG. 8  is an alignment chart in the parallel travel mode (second speed); 
         FIG. 9  is an alignment chart in the parallel travel mode (third speed); and 
         FIG. 10  is an alignment chart in a parallel travel mode (fourth speed). 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     With reference to  FIGS. 1 to 10 , a vehicle  1  and a drive unit according to the present embodiment will be described. In  FIGS. 1 to 10 , identical or substantially identical component members are designated by identical reference signs, and a redundant description thereof may be omitted. 
       FIG. 1  is a schematic view illustrating the overall configuration of the vehicle  1  according to the present embodiment. The vehicle  1  includes a drive unit  2 , driving wheels  90 , a control unit  100 , and a hydraulic circuit  500 . The drive unit  2  includes an engine  10 , a first MG (first rotary electric machine)  20 , a second MG (second rotary electric machine)  30 , a transmission unit constituted of a first planetary gear drive  40  and a second planetary gear drive  50 , a clutch (first clutch) C 1 , a clutch (second clutch) C 2 , and a brake B 1 . 
     The vehicle  1  travels with the motive power of at least one of the engine  10 , the first MG  20 , and the second MG  30 . The vehicle  1  may be a plug-in hybrid that is chargeable from an external power supply. 
     The drive unit  2  according to the present embodiment can operate in so-called an EV travel mode, a series travel mode, a series-parallel travel mode, and a parallel travel mode by controlling an engagement state of the clutch C 1 , the clutch C 2 , and the brake B 1  and driving of the first MG 1 , the second MG 2 , and the engine  10 . 
     The engine  10  is an internal combustion engine, such as a gasoline engine and a diesel engine, for example. 
     The first MG  20  and the second MG  30  each include a stator and a rotor provided rotatably with respect to the stator. The rotor has a permanent magnet embedded therein. The rotor of the first MG  20  is fixed to a rotating shaft  22 . The rotor of the second MG  30  is fixed to a rotating shaft  31 . The rotating shaft  22  is disposed on a first shaft  12 , while the rotating shaft  31  is disposed on a second shaft  14  parallel to the first shaft  12 . 
     On the first shaft  12 , the first MG  20 , the second planetary gear drive  50 , the first planetary gear drive  40 , the clutch C 2 , the clutch C 1 , and the engine  10  are disposed in sequence. 
     The second planetary gear drive  50  includes a sun gear S 2 , a plurality of pinion gears P 2 , a carrier CA 2  that connects each of the pinion gears P 2 , and a ring gear R 2 . The second planetary gear drive  50  is a single planetary gear. 
     The sun gear S 2  is fixed to the rotating shaft  22 . The ring gear R 2  is provided on an outer peripheral side of the sun gear S 2 , with the center of rotation being coaxial with the first shaft  12 . The carrier CA 2  is provided rotatably around the first shaft  12 . The carrier CA 2  supports each pinion gear P 2  in a rotatable manner. Each pinion gear P 2  is disposed between the sun gear S 2  and the ring gear R 2 . The pinion gears P 2  are provided so as to be able to revolve around the sun gear S 2  and to rotate around the central axis of the pinion gear P 1 . 
     The rotational speed of the sun gear S 2 , the rotational speed of the carrier CA 2 , and the rotational speed of the ring gear R 2  are in a relationship (relationship wherein when two rotational speeds out of the rotational speeds of the sun gear S 2 , the carrier CA 2 , and the ring gear R 2  are determined, the rotational speed of the remaining component are also determined) connected with a straight line in a later-described alignment chart. 
     The brake B 1  is provided in a casing  25  on an outer peripheral side of the ring gear R 2 . The brake B 1  is a hydraulic friction engagement element that can restrict rotation of the ring gear R 2 . When the brake B 1  is in an engagement state, the sun gear S 2  is fixed to the casing  25 , which restricts the rotation of the ring gear R 2 . When the brake B 1  is in a disengagement state, the rotation of the ring gear R 2  is permitted. 
     The first planetary gear drive  40  includes a sun gear S 1 , a plurality of pinion gears P 1 , a carrier CA 1  that connects each of the pinion gears P 1 , and a ring gear R 1 . The first planetary gear drive  40  is a single planetary gear. 
     The sun gear S 1 , which is fixed to the rotating shaft  22 , is provided rotatably around the first shaft  12 . Accordingly, the rotating shaft  22 , the sun gear S 1 , and the sun gear S 2  integrally rotate. The ring gear R 1  is provided on an outer peripheral side of the sun gear S 1 . The ring gear R 1  is provided rotatably around the first shaft  12 . 
     The ring gear R 1  is disposed on an outer peripheral side of the sun gear S 1 . The ring gear R 1  is provided rotatably around the first shaft  12 . The ring gear R 1  is connected to the carrier CA 2 , so that the ring gear R 1  and the carrier CA 2  integrally rotate. 
     Each of the pinion gears P 1  is disposed between the sun gear S 1  and the ring gear R 1  so as to gear with the sun gear S 1  and the ring gear R 1 . 
     The pinion gears P 1  are provided so as to be able to revolve around the sun gear S 1  and to rotate around the center of rotation of the pinion gears P 1 . 
     The carrier CA 1 , which rotatably supports each pinion gear P 1 , is provided rotatably around the first shaft  12 . 
     The rotational speed of the sun gear S 1 , the rotational speed of the carrier CA 1 , and the rotational speed of the ring gear R 1  are in a relationship (relationship wherein when two rotational speeds out of the rotational speeds of the sun gear S 1 , the carrier CA 1 , and the ring gear R 1  are determined, the rotational speed of the remaining component is also determined) connected with a straight line in an alignment chart as described later. 
     The clutch C 2  is a hydraulic friction engagement element that can couple the crankshaft  21  and the carrier CAL When the clutch C 2  is in an engagement state, the crankshaft  21  and the carrier CA 1  are coupled and rotate integrally with each other. When the clutch C 2  is disengaged, the carrier CA 1  is released from the coupled state with the crankshaft  21 . 
     The clutch C 1  is provided on a power transmission line from the engine  10  to the first MG  20 . The clutch C 1  is a hydraulic friction engagement element that can couple the rotating shaft  22 , the sun gear S 1 , and the sun gear S 2  with the crankshaft  21  of the engine  10 . When the clutch C 1  is in an engagement state, the rotating shaft  22 , the sun gear S 1 , the sun gear S 2 , and the crankshaft  21  are coupled, so that the motive power of the engine  10  can directly be transmitted to the first MG 1 . 
     When the clutch C 1  is disengaged, the crankshaft  21  of the engine  10  is released from the coupled state with the rotating shaft  22 , the sun gear S 1 , and the sun gear S 2 . As a result, it becomes impossible to directly transmit the motive power from the engine  10  to the first MG 1 . 
     The ring gear R 1  has outer peripheral teeth formed on the outer periphery thereof. The outer peripheral teeth gear with a driven gear  71 . The driven gear  71  is fixed to one end of a counter shaft  70 . The counter shaft  70  is disposed so as to be parallel to the first shaft  12  and the second shaft  14 . The other end of the counter shaft  70  is provided with a drive gear  72 . The drive gear  72  gears with a differential ring gear  81  of a differential gear  80 . The differential gear  80  is connected to a driving shaft  82 , and the driving shaft  82  is connected to the driving wheels  90 . Accordingly, rotation of the counter shaft  70  is transmitted to the driving wheels  90  through the differential gear  80 . 
     As a result, the motive power from the engine  10  and the first MG  20  is transmitted through the first planetary gear drive  40 , the second planetary gear drive  50 , and the driven gear  71  to the counter shaft  70 . 
     The rotating shaft  31  of the second MG  30  is fixed to a reduction gear  32 . The reduction gear  32  gears with the driven gear  71 . Accordingly, the motive power from the second MG  30  is transmitted to the counter shaft  70  through the reduction gear  32 . 
       FIG. 2  is a block diagram illustrating the configuration of the control unit  100  illustrated in  FIG. 1 . The control unit  100  includes an HV electric control unit (ECU)  150 , an MGECU  160 , and an engine ECU  170 . The HVECU  150 , the MGECU  160 , and the engine ECU  170  are each an electronic control unit configured to include a computer. The number of ECUs is not limited to three. All the ECUs may be integrated into one ECU, or one ECU may be divided into two, or four or more ECUs. 
     The MGECU  160  controls the first MG  20  and the second MG  30 . For example, the MGECU  160  regulates a current value supplied to the first MG  20  so as to control output torque of the first MG  20 . The MGECU  160  also regulates a current value supplied to the second MG  30  so as to control output torque of the second MG  30 . 
     The engine ECU  170  controls the engine  10 . For example, the engine ECU  170  performs control, such as control of the opening of an electronic throttle valve of the engine  10 , ignition control of the engine by outputting an ignition signal, and fuel injection control for the engine  10 . The engine ECU  170  controls the output torque of the engine  10  by such operation as control of the opening of the electronic throttle valve, injection control, and ignition control. 
     The HVECU  150  performs comprehensive control of the entire vehicle. The HVECU  150  is connected to sensors such as a vehicle speed sensor, an accelerator opening sensor, an MG 1  speed sensor, a MG 2  speed sensor, an output shaft speed sensor, and a battery sensor. With these sensors, the HVECU  150  acquires values such as a vehicle speed, an accelerator opening, the speed (rotational speed) of the first MG  20 , the speed (rotational speed) of the second MG  30 , the speed (rotational speed) of the output shaft of a transmission gear, and a battery state SOC. 
     The HVECU  150  calculates request values such as driving force, power, and torque requested to the vehicle, based on the acquired information. The HVECU  150  determines an output torque of the first MG  20 , an output torque of the second MG  30 , and an output torque of the engine  10  based on the calculated request values. The HVECU  150  outputs a command value of the MG 1  torque and a command value of the MG 2  torque to the MGECU  160 . The HVECU  150  outputs a command value of the engine torque to the engine ECU  170 . 
     The HVECU  150  controls the clutches C 1 , C 2  and the brake B 1  based on later-described travel modes or the like. The HVECU  150  outputs to the hydraulic circuit  500  in  FIG. 1  command values (PbC 1 , PbC 2 ) of the hydraulic pressure supplied to the clutches C 1 , C 2  and a command value (PbB 1 ) of the hydraulic pressure supplied to the brake B 1 , respectively. 
     Next, the details of control modes of the vehicle  1  will be described with reference to a differential engagement table and alignment charts. 
     
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                 MG 1 electric 
               
               
                   
                   
                   
                 C1 
                 C2 
                 B1 
                 lock 
               
               
                   
               
             
             
               
                 EV travel 
                   
                 MG2 single 
                 ◯ 
                   
                   
                   
               
               
                 mode 
                   
                 travel mode 
                   
                   
                   
                   
               
               
                   
                   
                 Dual-motor 
                   
                   
                 ◯ 
                   
               
               
                   
                   
                 travel mode 
                   
                   
                   
                   
               
               
                 HV travel 
                 Series 
                   
                 ◯ 
                   
                   
                   
               
               
                 mode 
                 Series-parallel 
                   
                   
                 ◯ 
                   
                   
               
               
                   
                 Parallel 
                 Gear stage 1 
                 ◯ 
                   
                 ◯ 
                   
               
               
                   
                   
                 Gear stage 2 
                   
                 ◯ 
                 ◯ 
                   
               
               
                   
                   
                 Gear stage 3 
                 ◯ 
                 ◯ 
                   
                   
               
               
                   
                   
                 Gear stage 4 
                   
                 ◯ 
                   
                 ◯ 
               
               
                   
               
             
          
         
       
     
     The table 1 illustrates each travel mode and the control states of the clutch C 1  and the clutch C 2  of the first planetary gear drive  40  and the brake B 1  in each of the travel modes. 
     The control unit  100  controls the vehicle  1  to travel in “a motor travel mode (hereinafter referred to as an EV travel mode)” or “a hybrid travel mode (hereinafter referred to as an HV travel mode).” 
     The EV travel mode is the mode of driving the vehicle  1  with the motive power of at least one of the first MG  20  and the second MG  30 , with the engine  10  being stopped. The HV travel mode is the mode of driving the vehicle  1  with the motive power of the engine  10  and the second MG  30  or the motive power of the engine  10 , the first MG  20  and the second MG  30 . In the present embodiment, the HV travel mode includes a series mode, a series-parallel mode, and a parallel mode. 
     In Table 1, “C 1 ”, “C 2 ”, “B 1 ”, “MG 1 ”, and “MG 2 ” represent the clutch C 1 , the clutch C 2 , the brake B 1 , the first MG  20 , and the second MG  30 , respectively. A circle mark (O) in each column of C 1 , C 2  and B 1  represents “engagement”, and no circle mark represents “disengagement.” 
     In the EV travel mode, the control unit  100  selectively switches, corresponding to a request torque and the like of the user, between “MG 2  single-travel mode” that drives the vehicle  1  with the motive power of only the second MG  30 , and “dual-motor travel mode” that drives the vehicle  1  with the motive power of both the first MG  20  and the second MG  30 . For example, when the load of the drive unit  2  is a low load, the single-travel mode is selected. When the load is a high load, the dual-motor travel mode is selected. 
     The HV travel mode is selected when the request torque requested from the user is not satisfied by the first MG  20  and the second MG  30 , or when the total fuel efficiency is determined to be better when the HV travel mode is selected than when the EV travel mode is selected. 
     In the HV travel mode, any one of the series travel mode, the series-parallel travel mode, and the parallel travel mode is selected. 
     In the series travel mode, all the motive power of the engine  10  is used as the motive power for generating electric power in the first MG  20 . The second MG  30  drives the driving wheels  90  using the electric power generated in the first MG  20 . 
     In the series-parallel travel mode, some of the motive power of the engine  10  is used to drive the driving wheels  90 , while the remaining motive power is used as the motive power for generating electric power in the first MG  20 . The second MG  30  drives the driving wheels  90  using the electric power generated in the first MG  20 . 
     In the series-parallel travel mode, the parallel travel mode is selected when the request torque from the user cannot be provided. 
     In the parallel travel mode, the driving wheels  90  are driven with the motive power from the first MG  20 , the second MG  30 , and the engine  10 . In the present embodiment, four stages can be configured as shift stages. 
       FIG. 3  is an alignment chart in the MG 2  single travel mode.  FIG. 4  is an alignment chart in the dual-motor travel mode.  FIG. 5  is an alignment chart in the series travel mode.  FIG. 6  is an alignment chart in the series-parallel travel mode.  FIGS. 7 to 10  are alignment charts in the parallel travel mode. 
     IN  FIGS. 3 to 10 , “Sun 1 ”, “Sun 2 ”, “Car 1 ”, “Car 2 ”, “Ring 1 ”, “Ring 2 ”, “ENG”, “MG 1 ”, “MG 2 ”, and “B 1 ” represent the sun gear S 1 , the sun gear S 2 , the carrier CA 1 , the carrier CA 2 , the ring gear R 1 , the ring gear R 2 , the engine  10 , the first MG  20 , the second MG  30 , and the brake B 1 , respectively. 
     With reference to  FIG. 3 , the control state during the MG 2  single travel mode will be described. As illustrated in Table 1, in the MG 2  single travel mode, the control unit  100  engages the clutch C 1 , and disengages the clutch C 2  and the brake B 1 . The control unit  100  also stops the engine  10 , and operates the second MG 2  as a motor. A second MG torque Tm 2  is transmitted to the driving wheels  90  through components such as the rotating shaft  31 , the reduction gear  32 , and the driven gear  71 . In this case, since the clutch C 1  is engaged, the crankshaft  21  and the rotating shaft  22  are coupled by the clutch C 1 . Since the engine  10  is stopped, the crankshaft  21  does not rotate, and the rotating shaft  22  coupled with the crankshaft  21  does not rotate either. Accordingly, the sun gears S 1 , S 2  do not rotate. 
     Meanwhile, since the clutch C 2  and the brake B 1  are disengaged, rotation of the ring gear R 2  and the carrier CA 2  is not restricted, and therefore the ring gear R 2  and the carrier CA 2  idly rotate with the rotation of the ring gear R 1 . 
     Thus, in the MG 2  single travel mode, the vehicle  1  travels using the torque (hereinafter referred to as a second MG torque Tm 2 ) from the second MG  30 . 
     A description is now given of the control state in the dual-motor travel mode with reference to  FIG. 4 . In the dual-motor travel mode, as illustrated in Table 1, the control unit  100  disengages the clutch C 1  and the clutch C 2 , and engages the brake B 1 . 
     Since the clutches C 1 , C 2  are disengaged, the engine  10  is in a state of being separated from the first planetary gear drive  40 . Since the brake B 1  is engaged, the ring gear R 2  is fixed to a casing  25 , so that the rotational speed of the ring gear R 2  becomes zero. 
     Then, the first MG  20  and the second MG  30  operate as a motor. Since rotation of the ring gear R 2  is restricted, the torque (hereinafter referred to as a first MG torque Tm 1 ) from the first MG  20  is transmitted to the driven gear  71  through the sun gears S 2 , S 1  and the ring gear R 1 . Furthermore, the second MG torque Tm 2  from the second MG  30  is also transmitted to the driven gear  71 . Thus, the first MG torque Tm 1  is added to the second MG torque Tm 2  from the second MG  30 , and is transmitted to the driving wheels  90 . 
     The control unit  100  regulates a share ratio of the first MG torque Tm 1  and the second MG torque Tm 2  so as to satisfy the request torque from the user. 
     With reference to  FIG. 5 , the control state in the series travel mode will be described. In the series travel mode, as illustrated in Table 1, the control unit  100  engages the clutch C 1 , and disengages the clutch C 2  and the brake B 1 . 
     Since the clutch C 1  is engaged, the rotating shaft  22  and the crankshaft  21  are coupled. Since the clutch C 2  and the brake B 1  are disengaged, the carrier CA 1  and the ring gear R 2  become rotatable. 
     Then, the engine  10  and the second MG  30  are driven. When the engine  10  is driven, the torque (hereinafter referred to as an engine torque Te) of the engine  10  is transmitted to the rotating shaft  22  through the clutch C 1 , and the first MG  20  generates electric power. 
     The second MG  30  operates as a motor using all or some of the electric power generated in the first MG  20 . Then, the vehicle  1  travels with the second MG torque Tm 2  from the second MG  30 . 
     With reference to  FIG. 6 , the control state in the series-parallel travel mode will be described. As illustrated in Table 1, in the series-parallel travel mode, the clutch C 1  and the brake B 1  are disengaged, and the clutch C 2  is engaged. 
     Since the clutch C 2  is engaged, the crankshaft  21  and the carrier CA 1  are coupled. In this state, the control unit  100  drives the engine  10  and the second MG  30 . 
     The engine torque Te from the engine  10  is transmitted to the carrier CA 1 . The first MG  20  functions as a generator. The first MG torque Tm 1  is used as reaction force for transmitting the engine torque Te to the ring gear R 1 . 
     The engine torque Te (hereinafter referred to as an engine transmitting torque Tec) transmitted to the ring gear R 1  is transmitted to the counter shaft  70  from the driven gear  71 , and acts as the motive power for driving the vehicle  1 . 
     In the series-parallel travel mode, the control unit  100  operates the second MG  30  mainly as a motor. The second MG torque Tm 2  is transmitted to the driving wheels  90  through the components such as the reduction gear  32 , the driven gear  71 , and the counter shaft  70 . 
     Thus, in the series-parallel travel mode, the vehicle  1  travels using the engine transmitting torque Tec and the second MG torque Tm 2 . 
     A description is now given of the control state in the parallel travel mode. The parallel travel mode includes first speed to fourth speed. 
     With reference to  FIG. 7 , the control state at the time of formation of the first speed will be described. As illustrated in Table 1, the control unit  100  engages the clutch C 1  and the brake B 1 , and disengages the clutch C 2 . Since the clutch C 1  is engaged, the crankshaft  21  and the rotating shaft  22  are joined through the clutch C 1 . Furthermore, since the brake B 1  is engaged, the ring gear R 2  is fixed to the casing  25 , so that the rotational speed of the ring gear R 2  becomes zero. 
     Then, the control unit  100  operates the engine  10 . When a high driving force is requested, the first MG  20 , the second MG  30 , or both the MGs are further operated as a motor. 
     Since the rotating shaft  22  and the crankshaft  21  are joined to each other, the speed of the rotating shaft  22  is in accord with the speed of the crankshaft  21 . The first MG torque Tm 1  and the engine torque Te are transmitted to the driven gear  71  from the ring gear R 1 . Furthermore, the second MG torque Tm 2  from the second MG  30  is also transmitted to the driven gear  71 . 
     With reference to  FIG. 8 , the control state at the time of formation of the second speed will be described. As illustrated in Table 1, the control unit  100  disengages the clutch C 1 , and engages the clutch C 2  and the brake B 1 . 
     Accordingly, the crankshaft  21  is coupled with the carrier CA 1  through the clutch C 2 . Furthermore, the ring gear R 2  is fixed to the casing  25  by the brake B 1  being engaged. 
     Then, the control unit  100  operates the engine  10 . When a high driving force is requested, the first MG  20 , the second MG  30 , or both the MGs are further operated as a motor. 
     The engine torque Te from the engine  10  is transmitted to the ring gear R 1  from the carrier CAL The first MG torque Tm 1  is also transmitted to the ring gear R 1  through the sun gears S 1 , S 2 . The first MG torque Tm 1  is then transmitted from the ring gear R 1  to the driving wheels  90  through the driven gear  71  and the like. The second MG torque Tm 2  is also transmitted to the driving wheels  90  through the reduction gear  32  and the like. 
     Here, in the state illustrated in  FIG. 7 , the crankshaft  21  is coupled with the sun gear S 1 , while in the state illustrated in  FIG. 8 , the crankshaft  21  is coupled with the carrier CAL Accordingly, a gear reduction ratio between the speed of the engine  10  and the speed of the ring gear R 1  is smaller in the state illustrated in  FIG. 8 . This indicates that the state illustrated in  FIG. 8  is higher in speed stage than the state illustrated in  FIG. 7 . 
     With reference to  FIG. 9 , the control state at the time of formation of the third speed will be described. As illustrated in Table 1, the control unit  100  engages the clutch C 1  and the clutch C 2 , and disengages the brake B 1 . Accordingly, each of the sun gears S 1 , S 2  and the carrier CA 1  is coupled with the crankshaft  21 . Since the carrier CA 2  is coupled with the ring gear R 1 , the sun gear S 1 , the carrier CA 1 , the ring gear R 1 , the sun gear S 2 , the carrier CA 2 , and the ring gear R 2  rotate at the same rotational speed. The control unit  100  operates the engine  10 . When a high driving force is requested, the first MG  20 , the second MG  30 , or both the MGs are further operated as a motor. 
     Then, the engine torque Te and the first MG torque Tm 1  are transmitted to the ring gear R 1 , and transmitted to the driven gear  71 . The second MG torque Tm 2  is also transmitted to the driven gear  71  through the reduction gear  32 . The vehicle  1  travels with the first MG torque Tm 1 , the second MG torque Tm 2 , and the engine torque Te. 
     Here, in the state illustrated in  FIG. 9 , the gear reduction ratio is one, whereas in the state illustrated in  FIG. 8 , the gear reduction ratio is larger than one. This indicates that the state illustrated in  FIG. 9  is higher in speed stage than the state illustrated in  FIG. 8 . 
     With reference to  FIG. 10 , the control state at the time of formation of the fourth speed will be described. As illustrated in Table 1, the control unit  100  disengages the clutch C 1  and the brake B 1 , and engages the clutch C 2 . Since the clutch C 2  is engaged, the crankshaft  21  and the carrier CA 1  are coupled through the clutch C 2 . 
     The control unit  100  controls the speed of the first MG  20  so that the rotational speed of the sun gear S 1  and the sun gear S 2  becomes zero (“electric lock” in Table 1). 
     To set the speed of the sun gears S 1 , S 2  to zero by using the first MG  20 , the current of the first MG  20  is feedback-controlled so that the rotational speed of the first MG  20  becomes zero, for example. 
     Then, the control unit  100  drives the second MG  30  and the engine  10 . 
     The engine torque Te of the engine  10  is transmitted to the ring gear R.  1  through the carrier CA 1 , and transmitted to the driving wheels  90 . The second MG torque Tm 2  is also transmitted to the driving wheels  90 . 
     As is clear from  FIG. 10 , in the state illustrated in  FIG. 10 , the gear reduction ratio is smaller than one, and a speed stage higher than that in the state illustrated in  FIG. 9  is formed. 
     Here, in the series travel mode, the vehicle travels with only the second MG torque Tm 2 , whereas in the series-parallel travel mode, the vehicle  1  travels with the second MG torque Tm 2  and the engine transmitting torque Tec. Accordingly, the series-parallel travel mode is higher in capable of outputting driving force than the series travel mode. 
     Accordingly, when the control unit  100  determines during traveling in the series travel mode that the driving force requested to the vehicle speed from the user is too large to supply in the series travel mode, the control unit  100  switches the travel mode to the series-parallel travel mode. 
     When the vehicle  1  according to the present embodiment makes a backward movement, the series travel mode is selected. In the series travel mode, the torque from the engine  10  is prevented from being transmitted to the counter shaft  70 . Accordingly, when the second MG  30  negatively rotates to cause negative rotation of the driven gear  71 , the second MG  30  is prevented from receiving the torque in a positive rotation direction from the engine  10 . In the series-parallel travel mode, when the vehicle  1  makes a backward movement, a direct torque of the positive rotation is added from the engine  10  to the driven gear  71 . As a result, the second MG  30  needs to generate a large second MG torque Tm 2  for backward movement of the vehicle  1 . 
     In the series-parallel travel mode, the first MG  20  functions as a generator, whereas in the parallel travel mode, the first MG  20  functions as a motor. Accordingly, the driving force that can be output in the parallel travel mode is higher than the driving force that can be output in the series-parallel travel mode. 
     Accordingly, when the vehicle is unable to supply the driving force requested from the user in the series-parallel travel mode, the control unit  100  selects the parallel travel mode. Generally, the two MGs (rotary electric machines) each have an ability to output the motive power close to the engine power. However, in the series travel mode or the series-parallel travel mode, the two MGs (rotary electric machines) have a disadvantage that full use of the MGs (rotary electric machines) as a power source is not available since the MGs function as transmissions of the engine power. At the same time, the vehicle according to the present embodiment is capable of outputting the sum of the driving force of the engine  10 , the driving force of the first MG  20 , and the driving force of the second MG  30 . 
     Specifically, the parallel travel mode in the mechanism illustrated in  FIG. 1  enables the vehicle to travel in the first to third speeds with only the engine  10  and without any of the first MG  20  and second MG  30 . When a large driving force is desired to be output, the vehicle can travel with the motive power of the first MG  20  and the second MG  30  being fully added to the engine power. 
     In the vehicle  1  according to the present embodiment, the first speed to fourth speed can be switched in the parallel travel mode. Therefore, at the time of climbing or acceleration, the first speed to the third speed can be used. In the series-parallel travel mode, high efficiency can be achieved even at the timing when energy efficiency deteriorates. Furthermore, adopting the fourth speed during high-speed traveling makes it possible to implement traveling with good energy efficiency even at the time of high speed. 
     As described in the foregoing, the drive unit  2  according to the present embodiment can select the EV travel mode, the series travel mode, the series-parallel travel mode, and the parallel travel mode. 
     Furthermore, the drive unit  2  is formed from two single pinion planetary gear drives, the clutches C 1 , C 2  and the brake B 1 . Therefore, reduction in the number of parts count and suppression of complicated configuration are also achieved. 
     It should be understood that the embodiment disclosed is in all respects illustrative and are not considered as the basis for restrictive interpretation. The scope of the present disclosure is defined not by the foregoing description but by the range of appended claim. All changes which come within the range of the claim and meaning and the range of equivalency thereof are therefore intended to be embraced therein. 
     The present disclosure is applicable to drive units.