Abstract:
A proposition is to provide a power transmitting mechanism for a hybrid vehicle having improved energy utilization efficiency. A power transmitting mechanism for the hybrid vehicle using powers of the engine and the motor/generator in a combined manner, the mechanism includes an engine drive shaft coupled to an engine output shaft via a main clutch; a motor output shaft of a motor/generator rotatably supported separately from the engine drive shaft; a drive shaft brake releasing/fixing the engine drive shaft; a motor-brake releasing/fixing the motor output shaft; and a planetary gear mechanism.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a U.S. National Stage application under 35 U.S.C. §371 claiming benefit of prior filed International Application Number PCT/JP2009/006189, filed Nov. 18, 2009, in which the International Application claims a priority date of May 25, 2009 based on prior filed Japanese Patent Application Number 2009-125543, the entire contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a power transmitting mechanism for hybrid vehicle that uses powers of an engine and a motor/generator by switching/combining them in accordance with situations. 
       BACKGROUND ART 
       [0003]    As disclosed in Non-Patent Documents 1 and 2 referred to hereinafter, in order to reduce a load on an engine to improve a mileage in a commercial car such as a truck, there has been recently proposed a hybrid system that uses the help of the motor at a time of starting and at a time of traveling in which a load is applied to an engine such as at a time of traveling on an uphill road. 
         [0004]      FIG. 10  illustrates a power transmission mechanism for hybrid vehicle disclosed in Non-Patent Document 1, and as illustrated in the drawing, regarding an arrangement of driving systems of the power transmitting mechanism, an engine  1 , a main clutch (single disk clutch)  3 , a motor (motor/generator)  5 , a transmission  7 , a final reduction gear  9  are all disposed coaxially in this order. Further, a rotor  13  of the motor  5  is attached to an engine drive shaft  11  that couples between the main clutch  3  and the transmission  7 , and a propeller shaft  15  is coupled between the transmission  7  and the final reduction gear  9 . 
         [0005]    Further, in the hybrid system, a vehicle starts to move using only a driving force of the motor  5  in a state of disengaging the main clutch  3 , rotations of the engine  1  and the motor  5  are synchronized at a specified vehicle speed (around about 5 to 6 km/h), and after the main clutch  3  is engaged, the vehicle starts to travel with the use of only the engine  1 . 
         [0006]    Further, it is structured such that at a time of traveling in which a load is applied such as when traveling on an uphill road, high-power traveling in which the engine  1  and the motor  5  are used in a combined manner in accordance with a depressing amount of an accel pedal is started to be performed, and at a time of deceleration/braking, by disengaging the main clutch  3  in accordance with situations and making the motor  5  to be inversely operated to apply a regenerative brake equivalent to an engine brake, a braking energy (regenerative energy) is collected in a battery. 
         [0007]    Further,  FIG. 11  illustrates a power transmitting mechanism for hybrid vehicle disclosed in Non-Patent Document 2, and in the power transmitting mechanism, a motor output shaft  19  is structured separately from an engine drive shaft  11 , and a clutch mechanism  21  formed of a dog clutch is attached between the motor output shaft  19  and the engine drive shaft  11 . 
         [0008]    Furthermore, as illustrated in  FIG. 12 , Patent Document 1 discloses a power transmitting mechanism for hybrid vehicle in which outputs of an engine  1  and a motor  5  are synthesized in a planetary gear mechanism  23  to be output to a transmission  7  side. 
         [0009]    As illustrated in the drawing, this power transmitting mechanism is characterized in that it is structured such that a ring gear  25  of the planetary gear mechanism  23  and a motor output shaft  19  of the motor  5  are coupled and a sun gear  27  of the planetary gear mechanism  23  and an engine drive shaft  11  are coupled to output power from a carrier  29  of the planetary gear mechanism  23  to the transmission  7  side, and meanwhile, when the ring gear  25 , the carrier  29 , and the sun gear  27  of the planetary gear mechanism  23  have mutually substantially the same predetermined coupling rotation speed, the carrier  29  and the ring gear  25  are integrally coupled through centrifugal clutches  31  to make a transmission ratio to be 1. 
         [0010]    Further, with the use of this power transmitting mechanism, when the engine  1  is driven to make the sun gear  27  rotate at a coupling rotation speed of the centrifugal clutches  31  when a vehicle is stopped, a regenerative braking is applied to the motor  5  which is in a state of being inversely rotated to smoothly stop the inverse rotation and operation of the motor is smoothly changed to a normal rotation powering, the vehicle starts to move smoothly, and when a rotation speed of the motor  5  is increased while controlling the driving of the engine  1  so that the sun gear  27  keeps rotating at the coupling rotation speed, a rotation speed of the ring gear  25  soon reaches the coupling rotation speed, and the carrier  27  and the ring gear  25  are integrally coupled through the centrifugal clutches  31 . 
         [0000]    Patent Document 1: Japanese Unexamined Patent Application Publication No. H09-14385
 
Non-Patent Document 1: “Monthly Automotive Engineering” October 2006 issue, published by TETSUDO-NIPPONSHA CO., LTD, pages 47-49.
 
Non-Patent Document 2: “Isuzu Technical Journal” No. 113,2005, published by Isuzu Motors Limited, pages 66-69
 
       DISCLOSURE 
     Problems to be Solved 
       [0011]    However, the power transmitting mechanism illustrated in  FIG. 10  has a disadvantageous point that, when the traveling is performed only by the driving force of the engine  1 , there occurs a loss (rotational resistance) due to idling of the motor  5 , namely, a mechanical loss due to an influence of magnet attached to the rotor  13 . Further, if a stator  33  of the motor  5  is electrified to eliminate such a load loss, an electrical loss is newly generated. 
         [0012]    Further, the power transmitting mechanism illustrated in  FIG. 11  can eliminate, because of its structure in which the motor output shaft  19  is structured separately from the engine drive shaft  11 , a mechanical loss (rotational resistance) caused by the motor  5  when the traveling is performed only by the driving force of the engine  1 , but, in order to smoothly perform engagement/disengagement of the dog clutch that forms the clutch mechanism  21 , highly accurate and complicated rotation speed synchronization control becomes necessary. 
         [0013]    Furthermore, the power transmitting mechanism using the dog clutch is assumed to be mounted on a small truck with a load capacity of 2 to 3 tons, and for the application to a large truck that requires a large motor output, insufficient strength and insufficient durability of the dog clutch have been a concern. 
         [0014]    Further, even in the power transmitting mechanism illustrated in  FIG. 12 , there has been a problem that a mechanical loss (rotational resistance) caused by the motor  5  is generated when the traveling is performed only by the engine  1 , similar to the conventional example in  FIG. 10 . 
         [0015]    The present invention has been devised in view of such actual circumstances, and a proposition thereof is to provide a power transmitting mechanism for hybrid vehicle in which an improvement is made on this type of power transmitting mechanism for hybrid vehicle that uses the powers of the engine and the motor/generator in a combined manner, the loss due to the rotational resistance of the motor/generator during when the traveling is performed only by the engine is eliminated, and in addition to that, energy utilization efficiency is improved by enabling input/output powers of the motor and the engine to be smoothly combined or separated. 
       Means for Solving the Problems 
       [0016]    In order to achieve such a proposition, according to a first aspect of the embodiment is a power transmitting mechanism for a hybrid vehicle having an engine, a main clutch, a motor/generator, a transmission, and a final reduction gear which are coaxially disposed, and using powers of the engine and the motor/generator in a combined manner, the power transmitting mechanism for the hybrid vehicle includes an engine drive shaft coupled to an engine output shaft via the main clutch; a motor output shaft of the motor/generator rotatably supported separately from the engine drive shaft; a drive shaft brake releasing/fixing the engine drive shaft; a motor-brake releasing/fixing the motor output shaft; and a planetary gear mechanism formed of a ring gear coupled to the motor output shaft, a sun gear coupled to the engine drive shaft, a plurality of planetary gears with which the sun gear and the ring gear are engaged, and a planetary carrier coupled to the transmission and receiving and transmitting orbital motions of the planetary gears, in which, by fixing the main clutch and releasing the drive shaft brake and the motor-brake, driving forces of the engine and the motor/generator are synthesized in the planetary gear mechanism to be transmitted to the transmission; by fixing the main clutch and the motor-brake and releasing the drive shaft brake, only the driving force of the engine is transmitted to the transmission from the planetary gear mechanism; by releasing the main clutch and the motor-brake and fixing the drive shaft brake, only the driving force of the motor/generator is transmitted to the transmission from the planetary gear mechanism, and the motor/generator is inversely operated when braking a vehicle to apply a regenerative brake; and by putting the engine in an idle state to fix the main clutch and inversely rotating the motor/generator to set an output from the planetary gears to “0”, the vehicle stops, and by changing the rotation of the motor/generator to a forward rotation side, the vehicle starts to move. 
         [0017]    Further, according to a second aspect of the embodiment is a power transmitting mechanism for a hybrid vehicle having an engine, a main clutch, a motor/generator, a transmission, and a final reduction gear which are coaxially disposed, and using powers of the engine and the motor/generator in a combined manner, the power transmitting mechanism for the hybrid vehicle includes an engine drive shaft coupled to an engine output shaft via the main clutch; a motor output shaft of the motor/generator rotatably supported separately from the engine drive shaft; a motor-brake releasing/fixing the motor output shaft; a planetary gear mechanism formed of a ring gear coupled to the motor output shaft, a sun gear coupled to the engine drive shaft, a plurality of planetary gears with which the sun gear and the ring gear are engaged, and a planetary carrier coupled to the transmission and receiving and transmitting orbital motions of the planetary gears; and a lock-up clutch releasing/fixing the planetary carrier and the ring gear, in which, by fixing the main clutch and releasing the motor-brake and the lock-up clutch, driving forces of the engine and the motor/generator are synthesized in the planetary gear mechanism to be transmitted to the transmission; by fixing the main clutch and the motor-brake and releasing the lock-up clutch, only the driving force of the engine is transmitted to the transmission from the planetary gear mechanism; by releasing the main clutch and the motor-brake and fixing the lock-up clutch, only the driving force of the motor/generator is transmitted to the transmission from the planetary gear mechanism, and the motor/generator is inversely operated when braking a vehicle to apply a regenerative brake; and by putting the engine in an idle state to fix the main clutch and inversely rotating the motor/generator to set an output from the planetary gears to “0”, the vehicle stops, and by changing the rotation of the motor/generator to a forward rotation side, the vehicle starts to move. 
       EFFECT 
       [0018]    According to the aspects of the embodiment, it becomes possible to achieve the starting and traveling of the vehicle in an engine drive mode for performing driving and braking with the use of only the engine, in a motor/engine cooperative drive mode for performing driving and braking using the driving forces of the engine and the motor/generator in a combined manner, and in a motor drive mode for performing driving and regenerative braking with the use of only the motor/generator. 
         [0019]    Further, according to the first and second aspects of the embodiment, there is an advantage that it is possible to perform, in the engine drive mode, traveling by conducting engagement/disengagement of the main clutch and a transmission operation of the transmission, similar to the conventional vehicle, and since the idling of the motor/generator is prevented, the engine does not have to generate an additional driving force. Further, at the time of braking, it is possible to use an enginebrake, but, by switching the mode to the motor drive mode, it is possible to use the regenerative braking provided by the motor/generator, and to efficiently collect a braking energy in a battery. 
         [0020]    Further, in the motor drive mode, by performing traveling in combination with the transmission operation of the transmission, starting, acceleration, and regenerative braking of the vehicle can be realized, and since the engine system is not used, efficient driving and regeneration can be performed. 
         [0021]    Further, it is possible to perform the motor drive mode in which the engine is in a stopped state or in an idling state, so that when the engine is stopped, it becomes possible to perform traveling in a noiseless vehicle interior and to perform noiseless traveling in a low-noise area. 
         [0022]    Further, in the motor/engine cooperative drive mode, it is possible to synthesize the engine driving force and the motor driving force while synchronizing the motor driving force with the engine driving force which is being gradually transmitted by the main clutch, which reduces the needless driving power of the motor/generator. 
         [0023]    Besides, as another driving method in the motor/engine cooperative drive mode, the main clutch is engaged to be “fixed”, and the motor/generator is inversely rotated while putting the engine in an idling state, to set the output from the planetary carrier of the planetary gear mechanism to “0”, which puts the vehicle in a stopped state, by making the rotation of the motor/generator change to the forward rotation side, the vehicle can start to move and accelerate, and by increasing the rotation speed of the inversely rotated motor/generator in a stopped state of the vehicle, the vehicle can be moved backward. 
         [0024]    Further, with the use of this driving method, there are various advantages such that the necessity for the engagement/disengagement operation of the main clutch which requires a delicate operation at the time of starting is eliminated, which enables performance of an easy start. 
         [0025]    Furthermore, according to the first and second aspects of the embodiment, since a sufficient strength of the planetary gear mechanism can be secured, it becomes possible to apply the inventions to a large truck that requires a large motor output. 
         [0026]    Further, according to the second aspect of the embodiment, by directly coupling the planetary carrier and the ring gear with the use of the lock-up clutch at the time of regenerative braking in the motor/generator, the planetary gear transmission of the planetary gear mechanism is eliminated, which enables to perform more efficient regeneration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a schematic structural diagram of a power transmitting mechanism according to one embodiment of claim  1 . 
           [0028]      FIG. 2  is an explanatory diagram of a power transmitting path in a motor drive mode. 
           [0029]      FIG. 3  is a collinear diagram regarding the motor drive mode. 
           [0030]      FIG. 4  is an explanatory diagram of a power transmitting path in a motor/engine cooperative drive mode. 
           [0031]      FIGS. 5  are collinear diagrams regarding the motor/engine cooperative drive mode. 
           [0032]      FIG. 6  is an explanatory diagram of a power transmitting path in an engine drive mode. 
           [0033]      FIG. 7  is a collinear diagram regarding the engine drive mode. 
           [0034]      FIG. 8  is a schematic structural diagram of a power transmitting mechanism according to a second aspect of the embodiment. 
           [0035]      FIG. 9  is an explanatory diagram of a power transmitting path in a motor drive mode. 
           [0036]      FIG. 10  is a schematic structural diagram of a conventional power transmitting mechanism. 
           [0037]      FIG. 11  is a schematic structural diagram of another conventional power transmitting mechanism. 
           [0038]      FIG. 12  is a schematic structural diagram of still another conventional power transmitting mechanism. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0039]    Hereinafter, embodiments of the present invention will be described in detail based on the drawings. 
         [0040]      FIG. 1  illustrates one embodiment of a power transmitting mechanism for hybrid vehicle according a first aspect of the embodiment, in which, similar to the conventional example in  FIG. 10 , regarding an arrangement of driving systems of the power transmitting mechanism according to the present embodiment, an engine  41 , a main clutch (single disk clutch)  43 , a motor (motor/generator)  45 , a transmission  47 , and a final reduction gear  49  are coaxially disposed in this order, an engine drive shaft  53  is coupled to an engine output shaft  51  via the main clutch  43 , and a propeller shaft  55  is coupled between the transmission  47  and the final reduction gear  49 . 
         [0041]    Further, in the drawing,  57  denotes a motor output shaft attached to a rotor  59  of the motor  45 , which is structured separately from the engine drive shaft  53  and rotatably supported by a not-illustrated motor body via a bearing. Further, to one end of the motor output shaft  57  on the main clutch  43  side, a motor-brake  61  that releases/fixes the motor output shaft  57  is attached. 
         [0042]    The motor-brake  61  is structured as a disk brake as an example, and it is designed such that when a brake disk  63  provided to the motor output shaft  57  is sandwiched between not-illustrated brake pads, a brake is applied to a rotation of the motor output shaft  57  to fix the motor output shaft  57  (fix the motor-brake  61 ), and further, when the brake pads are separated from the brake disk  63 , the brake on the motor output shaft  57  is released (the motor-brake  61  is released). 
         [0043]    Further, there is attached a drive shaft brake  65  which is adjacent to the motor-brake  61  and releases/fixes the engine drive shaft  53 . 
         [0044]    The drive shaft brake  65  is also structured as a disk brake as an example, and it is designed such that when a brake disk  67  provided to the engine drive shaft  53  is sandwiched between not-illustrated brake pads, a brake is applied to a rotation of the engine drive shaft  53  to fix the engine drive shaft  53  (fix the drive shaft brake  65 ), and further, when the brake pads are separated from the brake disk  67 , the brake on the engine drive shaft  53  is released (the drive shaft brake  65  is released). 
         [0045]    Further, there is provided, between the motor  45  and the transmission  47 , a planetary gear mechanism  69  that synthesizes driving forces of the engine  41  and the motor  45 . 
         [0046]    As illustrated in the drawing, the planetary gear mechanism  69  is formed of a ring gear  71  coupled to the motor output shaft  57 , a sun gear  73  coupled to the engine drive shaft  53 , a plurality of planetary gears  75  with which the sun gear  73  and the ring gear  71  are engaged, and a planetary carrier  77  receiving and transmitting an orbital motion of each of the planetary gears  75 , in which the planetary carrier  77  is coupled to the transmission  47  via a transmission shaft  79 . 
         [0047]    A power transmitting mechanism  81  according to the present embodiment is structured as above, and next, an operation thereof will be described based on  FIG. 2  to  FIG. 7 . 
         [0048]    First, when, for example, in an idling state or a stopped state of the engine  41 , the main clutch  43  is disengaged to be “released”, the brake disk  67  is sandwiched by the brake pads to “fix” the drive shaft brake  65  (engine drive shaft  53 ), and the brake pads are separated from the brake disk  63  to “release” the motor-brake  61  (motor output shaft  57 ) to rotate the motor  45  in a forward direction, as illustrated in  FIG. 2 , the rotation of the sun gear  73  coupled to the engine drive shaft  53  is regulated, so that each of the planetary gears  75  rotates around the sun gear  73  while rotating on its own axis, resulting in that the driving force of the motor  45  is transmitted to the transmission  47  from the transmission shaft  79 , and a vehicle starts to move using only a driving force of the motor  45  (motor drive mode). 
         [0049]    Therefore, by performing driving in combination with a transmission operation of the transmission  47 , the starting and acceleration of the vehicle can be achieved as illustrated in  FIG. 3 , and since the engine system is not used, the motor  45  is efficiently driven. 
         [0050]    Further, at the time of braking the vehicle, a torque from a tire  83  is input into the motor  45  via the planetary gear mechanism  69  to make the motor  45  inversely operate, so that a regenerative brake equivalent to an engine brake is applied, and a braking energy is collected in a battery. 
         [0051]    Further, when, after the vehicle starts to move in the motor drive mode in  FIG. 2  in an idling state of the engine  41 , the main clutch  43  is engaged to be “fixed”, and the brake pads are separated from the brake disk  67  to “release” the drive shaft brake  65  (engine drive shaft  53 ), as illustrated in  FIG. 4 , the brake on the sun gear  73  is released, so that as illustrated in  FIG. 5(   a ), the mode turns into the motor/engine cooperative drive mode in which the driving force of the motor  45  and the driving force of the engine  41  are synthesized in the planetary gear mechanism  69 . Further, at this time, it is possible to synthesize the engine driving force and the motor driving force while synchronizing the motor driving force with the engine driving force which is being gradually transmitted by the main clutch  43 , which reduces the needless driving power of the motor  45 . 
         [0052]    Further, as another driving method in the motor/engine cooperative drive mode, the main clutch  43  is engaged to be “fixed”, and the motor  45  is inversely rotated while putting the engine  41  in an idling state, to set the output from the planetary carrier  77  to “0” as in  FIG. 5(   b ), which puts the vehicle in a stopped state. Further, by making the rotation of the motor  45  change to the forward rotation side, the vehicle can start to move and accelerate as illustrated in  FIG. 5(   a ), and by increasing the rotation speed of the inversely rotated motor  45  in a stopped state of the vehicle as in  FIG. 5(   b ), the vehicle moves backward as illustrated in 
         [0053]      FIG. 5(   c ). 
         [0054]    With the use of the driving method as above, according to the present embodiment, it becomes possible to perform an easy start in which the necessity for the engagement/disengagement operation of the main clutch  43  which requires a delicate operation at the time of starting is eliminated. 
         [0055]    Next, explanation will be made on the engine drive mode utilizing only the driving force of the engine  41 . When, after the motor  45  is stopped and the engine  41  is started, the main clutch  43  is engaged to be “fixed”, and the brake disk  63  is sandwiched by the brake pads to “fix” the motor-brake  61  (motor output shaft  57 ), as illustrated in  FIG. 6 , the rotation of the ring gear  71  is regulated, so that each of the planetary gears  75  rotates around the sun gear  73  while rotating on its own axis with the driving force of only the engine  41 , resulting in that the driving force of the engine  41  is transmitted to the transmission  47  from the transmission shaft  79 , and the vehicle starts to move using only the driving force of the engine  41 . 
         [0056]    Further, by performing driving in combination with the transmission  47 , the starting and acceleration of the vehicle can be achieved as illustrated in  FIG. 7 , and since the motor system is not used, there is no mechanical loss caused by the motor  45 , and it is possible to perform traveling in a similar manner to that of the conventional vehicle. 
         [0057]    Further, in this engine drive mode, it is possible to use an engine brake at the time of braking, but, by switching the mode to the motor drive mode in  FIG. 2  at the time of braking, it is possible to efficiently collect the braking energy in the battery, as described above. 
         [0058]    Next, explanation will be made on a switching control among the above-described motor drive mode, engine drive mode, and motor/engine cooperative drive mode. For example, it is only required that a control unit (not illustrated) releases/fixes the motor-brake  61  and the drive shaft brake  65  as in  FIG. 2  to  FIG. 6 , in accordance with situations such as whether or not the vehicle is in a traveling state in which a load is applied to the engine  41  such as when the vehicle travels on an uphill road, and as an example, the control is performed such that, a battery capacity and a depressing amount of accel pedal are detected when the vehicle starts to travel, and when the accel pedal is depressed strongly at hill start and there is a sufficient battery capacity, the control unit “releases” the motor-brake  61  and the drive shaft brake  65  to drive the motor  45  as in  FIG. 4 , resulting in that high-power traveling in the motor/engine cooperative drive mode in which the driving forces of the engine  41  and the motor  45  are used in a combined manner, starts to be performed. 
         [0059]    Further, for example, when the accelerator is depressed strongly at hill start but the battery capacity for driving the motor  45  is insufficient, the control unit “fixes” the motor-brake  61  and “releases” the drive shaft brake  65  as in  FIG. 6 , resulting in that the vehicle travels by using only the driving force of the engine  41 . 
         [0060]    Further, when the vehicle starts to move on a smooth road and thus the accel pedal is depressed lightly, and besides, when the battery capacity is sufficient, the control unit “fixes” the drive shaft brake  65  and “releases” the motor-brake  61  as illustrated in  FIG. 2 , the mode turns into the motor drive mode, and the vehicle starts to move by using only the driving force of the motor  45 . Further, when, at a point at which the speed is increased, the control unit drives the engine  41  and “releases” the drive shaft brake  65 , and a driver engages the main clutch  43 , as illustrated in  FIG. 4 , the mode turns into the motor/engine cooperative drive mode in  FIG. 4 , and when the control unit determines that the battery capacity is insufficient when braking the vehicle, it “fixes” the drive shaft brake  65  and the driver disengages the main clutch  43  as illustrated in  FIG. 2  from the motor/engine cooperative drive mode in  FIG. 4 , resulting in that the regenerative brake equivalent to the engine brake is applied to the motor  45 , and the braking energy is collected in the battery. 
         [0061]    As described above, the present embodiment enables achievement of the starting and traveling of the vehicle in the engine drive mode in  FIG. 6  and  FIG. 7  for performing driving and braking with the use of only the engine  41 , in the motor/engine cooperative drive mode in  FIG. 4  and  FIGS. 5  the performance of driving and braking using the driving forces of the engine  41  and the motor  45  in a combined manner, and in the motor drive mode in  FIG. 2  and  FIG. 3  the performance of driving and regenerative braking with the use of only the motor  45 . 
         [0062]    Therefore, according to the present embodiment, 
         [0063]    [1] there is an advantage that it is possible to perform, in the engine drive mode, traveling by conducting the engagement/disengagement of the main clutch  43  and the transmission operation of the transmission  47 , similar to the conventional vehicle, and since the idling of the motor  45  is prevented, the engine  41  does not have to generate an additional driving force. 
         [0064]    Further, at the time of braking, it is possible to use the enginebrake, but, as described above, by switching the mode to the motor drive mode in  FIG. 2 , it is possible to use the regenerative braking provided by the motor  45 , and to efficiently collect the braking energy in the battery. 
         [0065]    Further, according to the present embodiment, 
         [0066]    [2] in the motor drive mode, the starting, acceleration, and regenerative braking of the vehicle can be realized by performing traveling in combination with the transmission operation of the transmission  47 , and since the engine system is not used, the efficient driving and regeneration can be performed. 
         [0067]    Further, it is possible to perform the motor drive mode in which the engine  41  is in a stopped state or in an idling state, so that when the engine  41  is stopped, it becomes possible to perform traveling in a noiseless vehicle interior and to perform noiseless traveling in a low-noise area. 
         [0068]    Further, according to the present embodiment, 
         [0069]    [3] in the motor/engine cooperative drive mode, it is possible to synthesize the engine driving force and the motor driving force while synchronizing the motor driving force with the engine driving force which is being gradually transmitted by the main clutch  43 , which reduces the needless driving power of the motor  45 . 
         [0070]    Besides, as described above, as another driving method in the motor/engine cooperative drive mode, the main clutch  43  is engaged to be “fixed”, and the motor  45  is inversely rotated while putting the engine  41  in an idling state, to set the output from the planetary carrier  77  to “0” as in  FIG. 5(   b ), which puts the vehicle in a stopped state, by making the rotation of the motor  45  change to the forward rotation side, the vehicle can start to move and accelerate as illustrated in  FIG. 5(   a ), and by increasing the rotation speed of the inversely rotated motor  45  in a stopped state of the vehicle as in  FIG. 5(   b ), the vehicle can be moved backward as illustrated in  FIG. 5(   c ). 
         [0071]    Further, with the use of this driving method, according to the present embodiment, there are various advantages such that it becomes possible to perform an easy start in which the necessity for the engagement/disengagement operation of the main clutch  43  which requires a delicate operation at the time of starting is eliminated. 
         [0072]    Furthermore, according to the present embodiment, the aforementioned operation and effect can be achieved, and in addition to that, a sufficient strength of the planetary gear mechanism  69  can be secured, so that it becomes possible to apply the present embodiment to a large truck that requires a large motor output. 
         [0073]      FIG. 8  illustrates one embodiment of a power transmitting mechanism for hybrid vehicle according to a second aspect of the embodiment, in which a power transmitting mechanism  85  according to the present embodiment is provided with, instead of the aforementioned drive shaft brake  65 , a lock-up clutch  87  that connects/disconnects a planetary carrier  77 - 1  of a planetary gear mechanism  69 - 1  coupled to the transmission  47  and a ring gear  71 - 1  coupled to the motor output shaft  57  (motor  45 ). 
         [0074]    As has been well known conventionally, the lock-up clutch  87  is a clutch mechanism used for improving power transmitting efficiency of a torque converter in an automatic car, and as illustrated in  FIG. 9 , the present embodiment is characterized in that it enables performance of starting, acceleration, and regenerative braking of the vehicle in combination with the transmission operation of the transmission  47  by coupling, at the time of regenerative braking of the motor  45 , the planetary carrier  77 - 1  and the ring gear  71 - 1  using the lock-up clutch  87 . 
         [0075]    Further, since the other structures of the power transmitting mechanism  85  according to the present embodiment and operations thereof are similar to those of the power transmitting mechanism  81  in  FIG. 1 , the same elements are denoted by the same reference numerals, and explanation of structures and explanation of operations will be omitted. 
         [0076]    Further, the present embodiment can also achieve a desired proposition, similar to the above-described embodiment, and by directly coupling, at the time of regenerative braking in the motor  45 , the planetary carrier  77 - 1  and the ring gear  71 - 1  using the lock-up clutch  87 , the planetary gear transmission of the planetary gear mechanism  69 - 1  is eliminated, resulting in that more efficient regeneration can be performed, compared with the power transmitting mechanism  81  in  FIG. 1 . 
         [0077]    The many features and advantages of the embodiments are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the embodiments that fall within the true spirit and scope thereof. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the inventive embodiments to exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope therof.