Abstract:
A hybrid vehicle comprises: a first driving force source; a transmission for transmitting the torque of the first driving force source therethrough to wheels; a second driving force source; and a torque transmitting route interposed between the driving force source and the wheels for inputting the torque of the second driving force source. The hybrid vehicle further comprises a torque adding route for synthesizing the torque outputted from the transmission and the torque transmitted from the second driving force source, to output the synthesized torque to an output member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vehicle which is constructed to transmit a torque of a driving force source through a transmission to wheels and, more particularly, to a hybrid vehicle in which a torque of another driving force source can be inputted to a torque transmitting route between one driving force source and the wheels. 
     2. Related Art 
     As well known in the art, an internal combustion engine outputs a kinetic energy by mixing and burning air and a fuel. As a result, the internal combustion engine discharges exhaust gases inevitably. The constituents and amount of the exhaust gases depend a running state of the internal combustion engine. According to the general tendency, not only the clarification of the exhaust gases but also the fuel economy are liable to become low at a high-load running time when the throttle opening is large. In recent years, on the contrary, a demand for the clarification of the exhaust gases of the vehicle having the internal combustion engine mounted thereon grows higher and higher. In order to satisfy this demand, there has been developed a hybrid vehicle which has an engine, an electric motor and a transmission mounted thereon. In this hybrid vehicle, the running state is judged on the basis of the accelerator opening and the vehicle speed to drive/stop the engine and the electric motor and to control a gear ratio of the transmission in accordance with the result of judgment. 
     One example of the hybrid vehicle thus having the engine, the electric motor and the transmission mounted thereon is disclosed in Japanese Patent Laid-Open No. 9-37411. According to this disclosure, the vehicle is constructed such that the torque of the engine is inputted through a planetary gear mechanism to a continuously variable transmission. On the other hand, the output side of the continuously variable transmission is connected to transmit the torque to the wheels. The continuously variable transmission is provided with an input rotary member, an output rotary member and a disc. These input rotary member and output rotary member are formed to have arcuate faces. Moreover, the disc is in contact with the arcuate face of the input rotary member and the arcuate face of the output rotary member. Th is continuously variable transmission is the so-called “toroidal type continuously variable transmission”. On the other hand, the output rotary member and the wheels are so connected as to transmit the torque. 
     The planetary gear mechanism includes a sun gear, a ring gear, and a carrier holding a pinion gear meshing with the sun gear and the ring gear. Moreover, the engine and the ring gear are connected in the torque transmittable manner, and the carrier and the input rotary member are connected in the torque transmittable manner. On the other hand, the sun gear and the electric motor are connected in the torque transmittable manner. Of the rotary element s of the planetary gear mechanism, moreover, the ring gear to which the torque of the engine is inputted acts as an input element. When this ring gear rotates, the sun gear to which the torque of the electric motor is inputted acts as a reaction element so that its torque is outputted from the carrier. The torque thus outputted from the carrier is inputted to the continuously variable transmission. In this continuously variable transmission, the gear ratio is set on the basis of a ratio between a radius of a contact point between the disc and the input rotary member and a radius of a contact point between the disc and the output rotary member. Therefore, the torque, as inputted to the continuously variable transmission, is decelerated or accelerated according to the gear ratio and transmitted to the wheels. 
     In the hybrid vehicle thus described, however, the high torque, as decelerated or synthesized by the planetary gear mechanism, is inputted to the continuously variable transmission. As a result, a slippage may occur between the torque transmitting members for transmitting the torque between the input side and the output side of the continuously variable transmission, that is, between input rotary member and the output rotary member, and the disc, to lower the transmission efficiency of the motive power. In order to prevent this slippage, on the other hand, the input/output members and the disc have to be brought into contact by a stronger force. The rise in this contact pressure may lower the transmission efficiency of the motive power. 
     SUMMARY OF THE INVENTION 
     A main object of the invention is to improve a transmission efficiency of a motive power in a transmission and to make the system compact. 
     A specific object of the invention is to improve a transmission efficiency of a motive power in a hybrid vehicle including at least two driving force sources and a continuously variable transmission. 
     Another object of the invention is to make compact an entire construction of a system including a mechanism for switching a drive state into a backward run. 
     According to a feature of the invention, there is provided a hybrid vehicle which comprises: a first driving force source; a transmission for transmitting the torque of the first driving force source therethrough to wheels; a second driving force source; and a torque transmitting route interposed between the first driving force source and the wheels for inputting the torque of the second driving force source. The hybrid vehicle further comprises a torque adding route for synthesizing the torque outputted from the transmission and the torque transmitted from the second driving force source, to output the synthesized torque to an output member. 
     The first driving force source can be constructed of an internal combustion engine, and the second driving force source can be constructed of an electric motor or a motor/generator. Moreover, the transmission can be constructed of a continuously variable transmission. 
     The torque of the second driving force source is added on the output side of the transmission to the output torque of the transmission. Therefore, the torque to be applied to the transmission is one to be transmitted from the first driving force source, i.e., a relatively low torque so that the transmission efficiency of the motive power in the transmission is improved. 
     Especially if the transmission is a belt type continuously variable transmission, the slippage of the belt is suppressed because of the low transmitted torque, and the transmission efficiency of the motive power is improved because a tension to be applied to the belt is lowered. 
     The torque adding route in the hybrid vehicle of the invention can be constructed of a Ravigneaux type planetary gear mechanism, one set of single-pinion type planetary gear mechanisms or a plurality of sets of planetary gear mechanisms. 
     When the torque adding route is constructed of the planetary gear mechanism, at least two high and low gear ratios can be set by the planetary gear mechanism. With this construction, it is possible to increase/decrease the torque to be outputted by the second driving force source. On the other hand, it is possible to change the RPM (i.e., revolutions per minute) of the case in which the second driving force source is forcibly driven. 
     When the torque adding route is constructed of the planetary gear mechanism, moreover, it is possible to give a forward/backward switching function to reverse and output the torque inputted. With this construction, the system can be made compact as a whole. 
     The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read with reference to the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustrations only and are not intended as a definition of the limits of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a skeleton diagram showing one embodiment of a hybrid vehicle according to the invention; 
     FIG. 2 is a block diagram showing a control system corresponding to the hybrid vehicle of FIG. 1; 
     FIG. 3 is a diagram tabulating corresponding relations between frictional engagement elements shown in FIG.  1  and individual drive patterns; 
     FIG. 4 is a nomographic diagram illustrating the states of rotary elements of a planetary gear mechanism in the embodiment of FIG. 1; 
     FIG. 5 is a diagram illustrating relations between a vehicle speed and a driving force in a control example according to the invention; 
     FIG. 6 is a skeleton diagram showing a hybrid vehicle according to another embodiment of the invention; 
     FIG. 7 is a nomographic diagram illustrating the states of rotary elements of a planetary gear mechanism in the embodiment of FIG. 6; 
     FIG. 8 is a skeleton diagram showing a hybrid vehicle according to another embodiment of the invention; and 
     FIG. 9 is a diagram tabulating corresponding relations between frictional engagement elements of the system shown in FIG.  8  and individual controls. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will be specifically described with reference to the accompanying drawings. On a hybrid vehicle according to the invention, there is mounted an engine  1 , as shown in FIG. 1, which can be exemplified by an internal combustion engine such as a gasoline engine, a Diesel engine or an LPG engine. Here will be conveniently described the case in which the gasoline engine is mounted as the engine  1 . This engine  1  can be exemplified by the well-known one provided with intake and exhaust units, a lubricating unit, a cooling unit, a fuel injection unit, an ignition unit, a starter unit and so on. 
     On the output side of the engine  1 , moreover, there is provided a continuously variable transmission (CVT)  2 . This continuously variable transmission  2  is disposed in a hollow casing K 1 . The continuously variable transmission  2  is equipped with an input shaft  3  and an intermediate shaft  4 , which are arranged in parallel with each other. On the other hand, the engine  1  is equipped with a crankshaft  5 , which is arranged coaxially with the input shaft  3 . On a torque transmitting route between the crankshaft  5  and the input shaft  3 , moreover, there is disposed a start clutch C 1 . This start clutch C 1  is a hydraulic type wet multi-disc clutch including a plurality of (not-shown) clutch plates, a plurality of (not-shown) clutch discs, a (not-shown) return spring and a (not-shown) hydraulic servo mechanism. 
     The continuously variable transmission  2  is further equipped with a drive-side pulley (or primary pulley)  6  and a driven-side pulley (or secondary pulley)  7 . The drive-side pulley  6  is disposed on the side of the input shaft  3 , and the driven-side pulley  7  is disposed on the side of the intermediate shaft  4 . The drive-side pulley  6  is equipped with a stationary sieve  8  and a movable sieve  9 . The stationary sieve  8  is fixed on the input shaft  3 , and the movable sieve  9  is made movable in the axial direction of the input shaft  3 . On the other hand, there is provided a hydraulic actuator  10  for moving the movable sieve  9  in the axial direction of the input shaft  3 . The hydraulic actuator  10  is well-known to include a (not-shown) piston for moving in the axial direction of the input shaft  3 , and a (not-shown) return spring. 
     On the other hand, the driven-side pulley  7  is equipped with a stationary sieve  11  and a movable sieve  12 . The stationary sieve  11  is fixed on the intermediate shaft  4 , and the movable sieve  12  is made movable in the axial direction of the intermediate shaft  4 . On the other hand, there is provided a hydraulic actuator  13  for moving the movable sieve  12  in the axial direction of the intermediate shaft  4 . The hydraulic actuator  13  is well-known to include a (not-shown) piston for moving in the axial direction of the intermediate shaft  4 , and a (not-shown) return spring. Moreover, a belt  14  is made to run on the drive-side pulley  6  and the driven-side pulley  7 . In other words, the torque is transmitted through the belt  14  between the drive-side pulley  6  and the driven-side pulley  7 . 
     Inside of the casing K 1 , on the other hand, there are disposed a motor/generator  15  and a torque adding route  16 . The motor/generator  15  has a function to convert a kinetic energy and an electric energy into each other. Specifically, the motor/generator  15  has both a function (or a power function) as an electric motor to output a torque according to an electric power supplied, and a function (or a regenerative function) as a power generator to generate an electric energy from a motive power inputted from the outside. 
     The torque adding route  16  transmits the torque of the motor/generator  15  to the output side of the continuously variable transmission  2  and is provided with a planetary gear mechanism  17 . This planetary gear mechanism  17  is the so-called “Ravigneaux type planetary gear mechanism” which is constructed by combining two planetary gear units. This planetary gear mechanism  17  is equipped with a first sun gear  18  and a first hollow shaft  19 . The first sun gear  18  is mounted on the intermediate shaft  4 . The first hollow shaft  19  is arranged so coaxially with and around the intermediate shaft  4  that it can rotate relative to the intermediate shaft  4 . A second sun gear  20  is mounted on the first hollow shaft  19 . On the other hand, a clutch C 2  is provided for controlling a torque transmitting state between the intermediate shaft  4  and the first hollow shaft  19 . On the inner face of the casing K 1 , moreover, there is disposed a first brake B 1  for controlling the rotation/stop of the first hollow shaft  19 . 
     Around the first sun gear  18 , on the other hand, there is arranged a ring gear  21 , which is meshed together with the second sun gear  20  by a second pinion gear  22 . On the other hand, these second pinion gear  22  and first sun gear  18  are meshed by a first pinion gear  23 . Coaxially with and around the intermediate shaft  4 , on the other hand, there is disposed a second hollow shaft  24  which can rotate relative to the intermediate shaft  4 . On the other hand, the second pinion gear  22  and the first pinion gear  23  are held by a carrier  25 , which is so connected to the second hollow shaft  24  as to transmit the torque. On the inner face of the casing K 1 , moreover, there is mounted a reverse brake BR for controlling the rotation/stop of the ring gear  21 . Still moreover, a gear  26  is formed on the second hollow shaft  24 . 
     Here, a gear  27  is formed on the outer circumference of the first hollow shaft  19 , and a gear  28  is formed on the output shaft  15 A of the motor/generator  15 . In parallel with the intermediate shaft  4 , on the other hand, there is disposed a shaft  29 A which is provided with a gear  29 . The gear  27  and the gear  28  are meshed with the gear  29 . 
     In parallel with the intermediate shaft  4 , on the other hand, there is disposed an output shaft  30 . This output shaft  30  is also disposed inside of the casing K 1 . The output shaft  30  is provided with a gear  31  and a gear  32 . Moreover, the gear  31  and the gear  26  mesh each other, and the gear  32  and wheels  33  are so connected through a (not-shown) differential gears as to transmit the torque. 
     A control system of the vehicle having the system shown in FIG. 1 will be described with reference to the block diagram of FIG.  2 . First of all, there is provided an electronic control unit (ECU)  34 . This electronic control unit  34  is provided for controlling the engine  1 , the continuously variable transmission  2  and the frictional engagement elements (i.e., the aforementioned various brakes and clutches). 
     The electronic control unit  34  is constructed to include a microcomputer composed mainly of a processing unit (e.g., CPU or MPU), storage units (e.g., RAM and ROM) and an input/output interface. To this electronic control unit  34 , there are inputted: a signal of an engine speed sensor  35 ; a signal of an accelerator depression sensor  36 ; a signal of a throttle opening sensor  37 ; a signal of a brake switch  38 ; a signal of a shift position sensor  39  for detecting an operating state of a (not-shown) shift lever; a signal of an input RPM sensor  40  for detecting the RPM (i.e., revolutions per minute) of the drive-side pulley  6 ; a signal of an output RPM sensor  41  for detecting the RPM of the driven-side pulley  7 ; and a signal of an output shaft RPM sensor  42  for detecting the RPM of the output shaft  30 . The vehicle speed is calculated on the basis of the signal of the output shaft RPM sensor  42 . 
     With the electronic control unit  34 , moreover, there are connected in a data communicable manner a fuel injection unit  43 , an ignition timing control unit  44  and a hydraulic control unit  45 . This hydraulic control unit  45  is equipped with a variety of solenoid valves  46  and a solenoid valve  47 . The various solenoid valves  46  are provided for controlling oil pressures to act on the start clutch C 1 , the clutch C 2 , the brake B 1  and the reverse brake BR on the basis of the operating state of the shift lever and other conditions. On the other hand, the solenoid valve  47  controls oil pressures to act on the hydraulic actuators  10  and  13 . 
     With the electronic control unit  34 , moreover, there is connected in a data communicable manner an electronic control unit  48  for the aforementioned motor/generator  15 . With this motor/generator  15 , on the other hand, there is electrically connected a battery  50  through an inverter  49 . Moreover, the motor/generator electronic control unit  48  is connected in a data communicable manner with the motor/generator  15 , the inverter  49  and the battery  50 . Moreover, the motor/generator electronic control unit  48  is provided with both a function to detect and control a current value to be fed to the motor/generator  15  from the battery  50  and a function to detect a current value of an electric energy generated by the motor/generator  15 . The motor/generator electronic control unit  48  is further provided with both a function to control the RPM of the motor/generator  15  and a function to detect and control the state of charge (SOC) of the battery  50 . 
     Here will be described the corresponding relations between the construction of the aforementioned embodiment and the construction of the invention. The engine  1  corresponds to the first driving force source of the invention, and the crankshaft  5 , the input shaft  3 , the intermediate shaft  4  and the output shaft  30  construct a route corresponding to the torque transmitting route of the invention. On the other hand, the motor/generator  15  corresponds to a second driving force source of the invention, and the gears  27 ,  28  and  29  and the first hollow shaft  19  construct a route corresponding to the torque adding route of the invention. 
     Here will be described the operations and controls of the hybrid vehicle having the construction thus far described. By operating the shift lever, there are selected either: a drive position for setting a state to transmit the torque (or motive power) of at least one of the engine  1  and the motor/generator  15  to the wheels  33 ; or a non-drive position for setting a state to transmit neither the torques of the engine  1  and the motor/generator  15  to the wheels  33 . The drive position is exemplified by a drive position or a reverse position, and a non-drive position is exemplified by a neutral position or a parking position. The drive position is a position for driving the vehicle forward, and the reverse position is a position for backing the vehicle. 
     When the drive position is selected, moreover, one of the various drive patterns is selected on the basis of the vehicle state, for example, the vehicle speed, the accelerator depression, the throttle opening or the shift position, for example, to make the control corresponding to the drive pattern. The drive patterns include the various patterns such as a creep run, an ordinary start, an ordinary run, a regenerative brake and a backward run, as tabulated in FIG.  3 . When the drive position is selected by the shift lever, moreover, it is possible to select any of the individual patterns of the creep run, the ordinary start, the ordinary run and the regenerative brake. When the reverse position is selected, on the other hand, the pattern of the backward run is selected. 
     The controls corresponding to the individual drive patterns will be described with reference to FIGS. 3 and 4. Of these, FIG. 3 tabulates the corresponding relations between the individual drive patterns and the states of the frictional engagement elements including the clutches and the brakes. FIG. 3 also tabulates the drive means (or the driving force sources of the vehicle) in the individual drive patterns. In FIG.  3 : “circle” symbols imply that the frictional engagement elements are applied; blanks imply that the frictional engagement elements are released; and a “triangle” symbol imply that the frictional engagement element is applied when the vehicle is quickly started (e.g., when the accelerator depression is large). On the other hand, FIG. 4 is a nomographic diagram illustrating the states of the first sun gear  18 , the second sun gear  20 , the carrier  25  and the ring gear  21  in the individual drive patterns. In FIG. 4, arrows designate the directions of rotations. 
     First of all, the creep run pattern is selected while there is active the so-called “ECO-run system”, as intended here to have the meaning of “ECOnomical-ECOlogical run”, for controlling the running/stopping of the engine  1  on the basis of a predetermined condition other than an operation of a (not-shown) ignition key. Specifically, this creep run pattern is selected, when a condition for returning the engine  1  to the running state is satisfied while the engine  1  is being automatically stopped under the engine stopping condition. More specifically, the creep run pattern is selected with a view to retaining the force for driving the wheels  33  for the time period from the satisfaction of the returning condition during the engine stop to the start of the engine  1 . Here, the condition for the engine stop is satisfied, for example, when the accelerator pedal is fully released, when the vehicle speed is at zero and when the brake switch  38  is turned ON. On the other hand, the returning condition is satisfied when at least one of the engine stopping conditions is dissatisfied. 
     In this creep run control, the clutch C 2  is applied, but the other clutches and the brakes are released. In short, the second sun gear  20  and the first sun gear  18  are directly connected. As a result, the torque, as outputted from the motor/generator  15 , is transmitted through the gears  28 ,  29  and  27  to the first sun gear  18  and the second sun gear  20 , and the first sun gear  18 , the second sun gear  20  and the carrier  25  rotate altogether, as shown in FIG.  4 . The torque of this carrier  25  is transmitted through the second hollow shaft  24  and the gear  26  to the output shaft  30 . The torque of this output shaft  30  is transmitted to the wheels  33  to generate the driving force of the wheels  33 . When the creep run pattern is thus selected, the vehicle runs by using the motor/generator  15  as the drive means. 
     Here will be described the ordinary start pattern. This ordinary start pattern is selected when the vehicle stops and when a demand for the start is made while the engine  1  is active. Whether or not the demand for the start is made is decided on the basis of the signal of the accelerator depression sensor  36 , the signal of the brake switch  38  and so on. When this ordinary start pattern is selected, the start clutch C 1  is applied, but the other clutches and the brakes are released. Then, the torque, as outputted from the crankshaft  5  of the engine  1 , is transmitted to the input shaft  3  of the continuously variable transmission  2 . The torque of the input shaft  3  is transmitted through the drive-side pulley  6 , the belt  14  and the driven-side pulley  7  to the intermediate shaft  4 . The torque thus transmitted to the intermediate shaft  4  is further transmitted through the first sun gear  18  and the first pinion gear  23  to the carrier  25 . 
     On the other hand, the torque of the motor/generator  15  is transmitted through the gears  28 ,  29  and  27  to the second sun gear  20 . As a result, the second sun gear  20  acts as a reaction element so that the carrier  25  is decelerated in its rotations with respect to the first sun gear  18 . On the other hand, the torque of the carrier  25  is transmitted through the second hollow shaft  24  and the gear  26  to the output shaft  30 . Specifically, the carrier  25  or the gear  26  to act as the output element is further decelerated in its rotations with respect to the intermediate shaft  4  by the planetary gear mechanism  17 . On the other hand, this torque of the carrier  25  or the gear  26  is a summed high torque of the torque to be transmitted from the engine  1  through the first sun gear  18  and the torque to be transmitted from the motor/generator  15  through the second sun gear  20 . 
     FIG. 5 is a diagram illustrating the relations between the vehicle speed and the driving force of the vehicle. In this diagram, there are illustrated: a running resistance of the vehicle; a (fundamental) driving force corresponding to a product which is calculated by multiplying the engine torque by the gear ratio; and a (hatched) zone in which the fundamental driving force is assisted by the motor/generator  15 . As seen from this driving force diagram of FIG. 5, the fundamental driving force is characterized to increase with the rise in the vehicle speed and to decrease at the instant when a predetermined vehicle speed is exceeded. 
     By selecting the ordinary start pattern, therefore, the driving force of the vehicle at a lower speed than a predetermined speed can be increased within a range of the assist zone. The driving force thus increased is substantially similar to that of the hybrid vehicle in which the so-called “torque converter” is disposed on the torque transmitting route between the engine and the continuously variable transmission. In other words, a torque amplifying function similar to that by the torque converter can be achieved by the motor/generator  15  and the planetary gear mechanism  17 . 
     When the ordinary start pattern is selected, more specifically, the output torque of the engine  1  is amplified by the continuously variable transmission  2  and the planetary gear mechanism  17 , and the torque, as outputted from the motor/generator  15 , is added to the output torque of the engine  1 , so that these summed torque is transmitted to generate the driving force of the wheels  33 . In other words, when the ordinary start pattern is selected, the engine  1  and the motor/generator  15  act as the drive means for the vehicle. 
     When the start demand made is a demand for a quick start, on the other hand, not only the start clutch C 1  but also the brake B 1  is applied. Whether or not this demand for the quick start is made is decided on the basis of whether the rate of change (or the changing ratio) of the accelerator depression per unit time exceeds a predetermined value. When the brake B 1  is thus applied, the second sun gear  20  is fixed, as illustrated in FIG.  4 . As a result, even when the torque to be transmitted to the intermediate shaft  4  abruptly rises, the backward rotation of the second sun gear  20  or the reaction element can be reliably prevented to retain the driving force of the wheels  33 . On the other hand, the brake B 1  can be controlled not only to the released/applied state but also to a slipping state. By receiving the reaction in this slipping state of the brake B 1 , the speed change at the continuously variable transmission  2  can be made in association with the motor/generator  15 . 
     When the vehicle is started to exceed a predetermined vehicle speed, moreover, the ordinary run pattern is selected. Then, the start clutch C 1  and the clutch C 2  are applied, but the other clutches and the brakes are released. When the engine torque is transmitted like before to the intermediate shaft  4 , therefore, the first sun gear  18 , the second sun gear  20  and the carrier  25  rotate altogether, as shown in FIG.  4 . Moreover, the torque of the carrier  25  is transmitted like before to the wheels  33 . When this ordinary run pattern is selected, therefore, the RPM of the output shaft  30  can be controlled within a range A 1  of FIG. 4 by controlling the gear ratio of the continuously variable transmission  2 . 
     Here will be described the control of the gear ratio of the continuously variable transmission  2 . In this continuously variable transmission  2 , the distance between the stationary sieve  8  and the movable sieve  9 , i.e., the groove width is adjusted by controlling the oil pressure to act on the hydraulic actuator  10 . On the contrary, the oil pressure to determine the groove width of the driven-side pulley  7  is controlled to give the belt  14  a tension according to the magnitude of the torque to be transmitted, so that the groove width of the driven-side pulley  7  changes with the change in the groove width of the drive-side pulley  6 . As a result, the winding radii of the belt  14  on the individual pulleys  6  and  7  change to control the gear ratio (i.e., the value calculated by dividing the RPM of the input shaft  3  by the RPM of the intermediate shaft  4 ) of the continuously variable transmission  2  steplessly (or continuously). 
     On the basis of the signals of the various sensors and other data, on the other hand, the electronic control unit  34  controls the engine  1 , the continuously variable transmission  2  and the various frictional engagement elements. For these controls, the electronic control unit  34  are stored in advance with the various data such as shift maps therefor and optimum fuel economy curves for the engine. The shift maps for the continuously variable transmission are prepared for controlling the gear ratio of the continuously variable transmission  2  and are set with such a gear ratio for the continuously variable transmission  2  as matches the vehicle state such as the accelerator depression (or the throttle opening) and the vehicle speed. 
     On the other hand, the optimum fuel economy curves for the engine are prepared for deciding the propriety of the fuel economy by using the conditions of the engine torque, the engine RPM and so on as parameters. On the basis of the vehicle speed, the accelerator depression and so on, moreover, a demand for an acceleration is decided so that a target engine output is determined as based on the result of the decision. On the basis of these operation results and the optimum fuel economy curves, the target engine RPM is determined to control the gear ratio of the continuously variable transmission  2  so that the actual engine RPM may approach the target one. The shift control of the continuously variable transmission  2  and the control of the engine RPM are applied to the ordinary start pattern or the ordinary run pattern. 
     When the aforementioned backward run pattern is selected, the start clutch C 1  and the reverse brake BR are applied, but the other brakes and clutches are released. In short, the ring gear  21  is brought into the fixed state. When the torque of the intermediate shaft  4  is transmitted to the first pinion gear  23 , therefore, the ring gear  21  acts as the reaction element, and the carrier  25  rotates in the opposite direction to the rotations of the other drive patterns. Here, no torque is transmitted from the motor/generator  15 . Thus, the engine  1  acts as the drive means for the vehicle when the backward run pattern is selected. 
     Here will be described the controls of the regenerative brake pattern. This regenerative brake pattern is selected while the vehicle is being decelerated, that is, while vehicle is coasting. When this regenerative brake pattern is selected, the clutch C 2  is applied, but the remaining clutches and the brakes are released. In accordance with this coasting run, moreover, the motive power (i.e., the kinetic energy) of the wheels  33  is transmitted through the gear  32 , the output shaft  30  and the gear  31  to the gear  26 . Moreover, the motive power of this gear  26  is transmitted through the carrier  25  to the first sun gear  18  and the second sun gear  20 . 
     With the clutch C 2  being applied, the first sun gear  18  and the second sun gear  20  are directly connected so that the motive powers of the first sun gear  18  and the second sun gear  20  are transmitted together through the gears  27 ,  29  and  28  to the motor/generator  15 . Moreover, this motor/generator  15  functions as the power generator so that the electric energy generated is charged through the inverter  49  into the battery  50 . 
     In the embodiment as has been described with reference to FIGS. 1 to  5 , the torque, as outputted from the continuously variable transmission  2 , can be transmitted to the wheels  33  after it is amplified by the motor/generator  15  and the planetary gear mechanism  17 . In other words, the control range of the gear ratio of the continuously variable transmission  2  is apparently widened. With respect to the torque to be transmitted to the wheels  33  in response to a demand for an acceleration, therefore, the torque to be inputted from the engine  1  to the continuously variable transmission  2  can be made as low as possible. In the continuously variable transmission  2 , therefore, the slippage of the contacting portions between the drive-side pulley  6  and the driven-side pulley  7  and the belt  14  is suppressed to improve the transmission efficiency of the motive power in the continuously variable transmission  2  and the durability of the continuously variable transmission  2 . From another aspect, the torque to be transmitted by the continuously variable transmission  2  can be lowered to make the drive-side pulley  6 , the driven-side pulley  7  and the belt  14  more compact. 
     Moreover, the driving force at the time of starting the vehicle can be increased (or assisted) by the functions of the motor/generator  15  and the planetary gear mechanism  17  thereby to improve the starting performance of the vehicle. This assist zone by the motor/generator  15  is determined by the demand for an acceleration such as the accelerator depression and the vehicle speed. When the regenerative brake pattern is selected, moreover, the motor/generator  15  is caused to function as the power generator by the running inertia transmitted from the wheels  33 , so that the electric energy generated can be recovered. 
     With respect to the wheels  33 , on the other hand, the motor/generator  15  and the continuously variable transmission  2  are arranged in parallel, and the start clutch C 1  is released at the regenerative brake controlling time. As a result, the motive power of the wheels  33  is not transmitted to the engine  1  so that the motive power to be transmitted from the wheels  33  is not consumed by dragging the engine  1 . As a result, it is possible to improve the power generation efficiency by the motor/generator  15 , i.e., the electric energy recovery efficiency. When the clutch C 2  is applied, on the other hand, the first sun gear  18  and the second sun gear  20  rotate together so that the motor/generator  15  can be rotated to function as the power generator at an RPM according to that of the output shaft  30  being decelerated. 
     In order that the motor/generator  15  may transmit the torque to the second sun gear  20  of the planetary gear mechanism  17 , on the other hand, the gears  27 ,  28  and  29  are provided separately of the planetary gear mechanism  17 . This makes it possible to construct the system of FIG. 1 merely by adding the motor/generator  15  and the gears  27 ,  28  and  29  newly to the existing system having the continuously variable transmission  2  and the planetary gear mechanism  17 . In other words, the components can be shared with the existing system, so that the hybrid vehicle of the invention can be provided merely by changing the existing system partially. Moreover, the construction is made such that the motor/generator  15  is separately attached to the outside of the continuously variable transmission and the planetary gear mechanism  17 . This makes it possible to employ a motor/generator of excellent mass productivity. For these reasons, it is possible to suppress the cost for manufacturing the hybrid vehicle. 
     In the ordinary start pattern or the ordinary run pattern, on the other hand, the gear ratio of the planetary gear mechanism  17  can be controlled at two steps by applying the brake B 1  or the clutch C 2 . 
     FIG. 6 is a skeleton diagram showing another embodiment of the invention. Of the components of FIG. 6, the description of the components shared with the construction of FIG. 1 will be omitted by designating them by the same reference numerals as those of FIG.  1 . On the output side of the continuously variable transmission  2 , there is disposed a hollow shaft  51 , in which such a shaft  52  is disposed as can rotate relative to the hollow shaft  51 . Moreover, a shaft  53  is provided in parallel with the shaft  52 . 
     The stationary sieve  11  of the aforementioned driven-side pulley  7  is fixed on the hollow shaft  51 , and the movable sieve  12  is so disposed as to move in the axial direction of the hollow shaft  51 . There is also provided the hydraulic actuator  13  for moving the movable sieve  12  in the axial direction of the hollow shaft  51 . 
     On the other hand, a planetary gear mechanism  54  is provided for controlling the state of the torque transmission between the hollow shaft  51  and the shaft  53 . The continuously variable transmission  2  and the planetary gear mechanism  54  are disposed in a casing K 2 . This planetary gear mechanism  54  is provided with a first planetary gear unit  55  and a second planetary gear unit  56 , which are arranged on the common axis. The first planetary gear unit  55  is arranged closer to the continuously variable transmission  2  than the second planetary gear unit  56 . The first planetary gear unit  55  is composed of: a first sun gear  57 ; a first ring gear  58  disposed concentrically of the first sun gear  57 ; and a first carrier  60  for holding a first pinion gear  59  meshing with the first sun gear  57  and the second ring gear  58 . In short, the first planetary gear unit  55  is a single-pinion type planetary gear unit. 
     On the other hand, the second planetary gear unit  56  is a single-pinion type planetary gear unit composed of: a second sun gear  61 ; a second ring gear  62  disposed concentrically of the second sun gear  61 ; and a second carrier  64  for holding a second pinion gear  63  meshing with the second sun gear  61  and the second ring gear  62 . Outside of the first ring gear  58  and the second ring gear  62 , there is disposed a connecting drum  65 , which is integrally connected to the first ring gear  58  and the second carrier  64 . On the other hand, the shaft  52  is arranged at its one end inside of the connecting drum  65 . The end portion of the shaft  52  on the inner side of the connecting drum  65  is integrally connected to the second ring gear  62 . There is also provided the clutch C 2  for controlling the state of the torque transmission between the first carrier  60  and the hollow shaft  51 . On the side of the casing K 2 , moreover, there is disposed the reverse brake BR for controlling the rotation/stop of the first carrier  60 . 
     To the outer end portion of the connecting drum  65 , there is attached a shaft  66  which is disposed coaxially of the shaft  52 . A gear  67  is formed on the shaft  66 . On the aforementioned shaft  53 , there are formed gears  68  and  69 , of which the gear  68  meshes with the gear  67 . Moreover, the gear  69  is so connected through the (not-shown) differential gears to the wheels  33  as to transmit the torque. 
     At the other end of the casing K 2 , i.e., on the side opposed to the position of the drive-side pulley  6 , on the other hand, there is disposed the motor/generator  15 , the output shaft  70  of which is arranged in parallel with the shaft  53 . A gear  71  is formed on the output shaft  70 . On the side of the casing K 2 , on the other hand, there is disposed the brake B 1  for controlling the rotation/stop of the output shaft  70 . A gear  72  is formed on the shaft  52 , and a shaft  73  is disposed in parallel with the shaft  52  and the output shaft  70 . On the shaft  73 , there is formed a gear  74 , which meshes with the gears  72  and  71 . The control system of FIG. 2 can also be employed as that of this system of FIG.  6 . 
     Here will be described the corresponding relations between the embodiment shown in FIG.  6  and the invention. The input shaft  3 , the hollow shaft  51 , the shaft  66 , the output shaft  53  and the gears  67 ,  68  and  69  construct a route corresponding to the torque transmitting route of the invention. On the other hand, the output shaft  70 , the gears  71 ,  74  and  72  and the shafts  52  and  73  construct a route corresponding to the torque adding route of the invention. 
     The drive patterns to be selected by the system of FIG. 6 are individually identical to those of FIG.  3 . Therefore, the control contents of the system of FIG. 6 will be described with reference to FIG.  7 . FIG. 7 is a nomographic diagram illustrating the states in the individual drive patterns of the first sun gear  57 , the second sun gear  61 , the first carrier  60 , the first ring gear  58 , the second carrier  64  and the second ring gear  62 . 
     First of all, when the creep run pattern is selected, the clutch C 2  is applied, but the other brakes and clutches are released, so that the torque of the motor/generator  15  is transmitted through the gears  71 ,  74  and  72  to the shaft  52 . Then, as shown in FIG. 7, the second sun gear  61 , the second carrier  64  and the second ring gear  62  rotate altogether so that their torque is transmitted through the connecting drum  65  to the shaft  66 . The torque of this shaft  66  is transmitted through the gears  67  and  68  to the output shaft  53 , and the torque of this output shaft  53  is transmitted to generate the driving force of the wheels  33 . Here in this creep run pattern, the torque of the engine  1  is not transmitted yet to the input shaft  3 . In the embodiment shown in FIG. 6, therefore, the motor/generator  15  acts as the drive means for the vehicle when the creep run pattern is selected. 
     Next, when the ordinary start pattern is selected, the start clutch C 1  is applied, but the other clutches and brakes are released. Then, the torque, as outputted from the crankshaft  5  of the engine  1 , is transmitted through the continuously variable transmission  2  to the hollow shaft  51  and the second sun gear  61 . On the other hand, the torque of the motor/generator  15  is transmitted through the shaft  52  to the second ring gear  62 . Then, the second ring gear  62  is fixed to act as the reaction element, as shown in FIG.  7 . As a result, at the instant when the vehicle starts, the second ring gear  62  is fixed to act as the reaction element, and the second carrier  64  rotates at a lower speed than that of the second sun gear  61  so that the torque is outputted from the second carrier  64 . 
     Thus, by the torque of the motor/generator  15 , the RPM of the output shaft  53  (or the output RPM) can be controlled within a range D 1 . When the torque to be transmitted through the continuously variable transmission  2  to the hollow shaft  51  abruptly rises as at a quick start, the second ring gear  62  can be reliably fixed by applying the brake B 1 . 
     When the ordinary run pattern is selected, moreover, the start clutch C 1  and the clutch C 2  are applied, but the other clutches and the brakes are released. When the engine torque is transmitted like before to the hollow shaft  51 , therefore, the first sun gear  57 , the first carrier  60  and the first ring gear  58  rotate altogether, as shown in FIG.  7 . As a result, when this ordinary run pattern is selected, the output RPM can be controlled within a range E 1  by controlling the gear ratio of the continuously variable transmission  2 . 
     When the ordinary run pattern is selected, on the other hand, the torque of the motor/generator  15  can be added to the output torque of the continuously variable transmission  2  in accordance with the degree of a demand for an acceleration by transmitting the torque of the motor/generator  15  through the second ring gear  62  to the second carrier  64 . When the ordinary run pattern is thus selected, at least the engine  1  is employed as the drive means for the vehicle. 
     When the backward run pattern is selected, still moreover, the start clutch C 1  and the reverse brake BR are applied, but the other brakes and clutches are released. In short, the first carrier  60  is fixed. When the output torque of the continuously variable transmission  2  is transmitted to the first sun gear  57 , therefore, the first ring gear  58  rotates in the opposite direction to and at a lower speed than the first sun gear  57 , as illustrated in FIG.  7 . As a result, the direction of rotation of the output shaft  53  is reversed from that of the remaining drive patterns so that the vehicle runs backward. When this backward run pattern is selected, no torque is outputted from the motor/generator  15 . When the backward run pattern is thus selected, the drive means for the vehicle is the engine  1 . 
     When the vehicle comes into the coasting state so that the regenerative brake pattern is selected, the clutch C 2  is applied, but the other clutches and the brakes are released. Then, the running inertia, as inputted from the wheels  33 , is transmitted through the gear  69 , the output shaft  53  and the gears  68  and  67  to the shaft  66 . When the torque of the shaft  66  is further transmitted to the connecting drum  65 , the second carrier  64 , the second ring gear  62  and the second sun gear  61  rotate altogether. Moreover, the torque of the shaft  51  is transmitted through the gears  72 ,  74  and  71  to the motor/generator  15 . Then, the motor/generator  15  functions as the power generator. The electric energy generated is charged through the inverter  49  into the battery  50 . 
     In the embodiment thus far described with reference to FIG. 6, too, the torque, as outputted from the continuously variable transmission  2 , can be amplified by the functions of the motor/generator  15  and the planetary gear mechanism  54  and transmitted to the wheels  33 . Therefore, effects similar to those of the embodiment shown in FIGS. 1 to  5  can also be obtained from the embodiment shown in FIG.  6 . Here, the embodiments of FIGS. 1 to  7  can be applied to an FF vehicle (i.e., a front-engine front-drive vehicle) and an FR vehicle (i.e., a front-engine rear-drive vehicle). 
     Here, there has been proposed in the prior art the hybrid vehicle which can aid (or assist) the output of the engine with the function of the electric motor while the vehicle is running. In this hybrid vehicle, the electric motor is arranged on the output side of the engine, and the transmission is disposed on the torque transmitting route between the electric motor and the wheels. In this hybrid vehicle, on the other hand, the electric motor is caused to function as the power generator, while the vehicle is being decelerated, by transmitting the motive power inputted from the wheels to the electric motor, so that the electric energy generated can be recovered. 
     In this hybrid vehicle, the reduction ratio of the transmission has to be set high so that a high assist torque may be obtained while making the size of the electric motor as small as possible. When the reduction ratio of the transmission is set high, however, such a problem arises if the vehicle runs at a high speed at a high gear ratio of the transmission that the electric motor is overheated as its RPM exceeds the allowable value. 
     On the other hand, the transmission is provided with the frictional engagement elements to be operated by a hydraulic control, such as the wet-type multi-disc clutch or the band brake. If the gear ratio of the transmission is to be set high as before, therefore, there arises a problem that the structure of the system including the frictional engagement elements is made complex and heavy. On the other hand, there is complicated the switching timing or the hydraulic control of applying/releasing the frictional engagement elements. As a result, a control circuit is needed for the electronic control unit which is provided for controlling the application/release and the oil pressure of the frictional engagement elements. For these reasons, there may arise the cost for manufacturing the hybrid vehicle. Therefore, an embodiment of the hybrid vehicle capable of solving those problems will be described with reference to FIG.  8 . 
     A hybrid vehicle shown in FIG. 8 belongs to the FF (i.e., the front engine front-drive) type vehicle. The crankshaft  5  of the engine  1  is equipped with a flywheel  75 . In FIG. 8, moreover, there is adopted the so-called “transverse engine type”, in which the crankshaft  5  is arranged in the transverse direction of the vehicle. On the other hand, an input shaft  76  is disposed coaxially of the crankshaft  5 . A damper  77  is disposed on the torque transmitting route between the input shaft  76  and the flywheel  75 . 
     There is provided a first planetary gear mechanism  78  which corresponds to that input shaft  76 . The first planetary gear mechanism  78  is disposed in a casing K 3 . This first planetary gear mechanism  78  is composed of: a sun gear  79  formed on the input shaft  76 ; a ring gear  80  disposed outside of the sun gear  79 ; a first pinion gear  81  meshing with the sun gear  79 ; a second pinion gear  82  meshing with the first pinion gear  81  and the ring gear  80 ; and a carrier  83  holding the first pinion gear  81  and the second pinion gear  82 . In short, the first planetary gear mechanism  78  is the so-called “double-pinion type planetary gear mechanism”. 
     For this first planetary gear mechanism  78 , on the other hand, a clutch C 0  and a brake B 0  are provided on the side of the casing K 3 . The clutch C 0  controls the state of the torque transmission between the carrier  83  and the input shaft  76 , and the brake B 0  controls the rotation/stop of the ring gear  80 . 
     To the carrier  83 , moreover, there is connected a hollow shaft  84 , which is so coaxially mounted around the input shaft  76  so that the hollow shaft  84  and the input shaft  76  can rotate relative to each other. On the other hand, there is provided an intermediate shaft  85  in parallel with the input shaft  76 . Inside of the casing K 3 , moreover, there is disposed the continuously variable transmission  2  for effecting the mutual torque transmission between the input shaft  76  and the intermediate shaft  85 . Of the construction of the continuously variable transmission  2  of FIG. 8, the description of the same portions as those shown in FIG. 1 will be omitted by designating them by the common reference numerals. 
     The stationary sieve  8  of the drive-side pulley  6  is fixed on the hollow shaft  84 . Moreover, the movable sieve  9  of the drive-side pulley  6  is made movable in the axial direction of the hollow shaft  84 . On the other hand, the stationary sieve  11  of the driven-side pulley  7  is fixed on the intermediate shaft  85 . Moreover, the movable sieve  12  of the driven-side pulley  7  is made movable in the axial direction of the intermediate shaft  85 . 
     Inside of the casing K 3 , moreover, the motor/generator  15  is disposed coaxially of the intermediate shaft  85 . On the torque transmitting route between the intermediate shaft  85  and the motor/generator  15 , on the other hand, there is disposed a second planetary gear mechanism  86 . This second planetary gear mechanism  86  is composed of: a sun gear  88  formed on the output shaft  87  of the motor/generator  15 ; a ring gear  89  arranged concentrically with respect to the sun gear  88 ; and a carrier  91  holding a pinion gear  90  meshing with the sun gear  88  and the ring gear  89 . The carrier  91  is connected to one axial end of the intermediate shaft  85 . In short, the second planetary gear mechanism  86  is a single-pinion type planetary gear mechanism. 
     On the other hand, the ring gear  89  is formed on the inner circumference of a connecting drum  92 . Moreover, a first one-way clutch F 1  is mounted at its inner race on the intermediate shaft  85  and at its outer race on the connecting drum  92 . Moreover, a second one-way clutch F 2  is mounted at its inner race on the connecting drum  92 . On the side of the casing K 3 , there is disposed the brake B 1  for controlling the rotation/stop of the outer race of the second one-way clutch F 2 . 
     At the end portion of the intermediate shaft  85  on the side of the engine  1 , there is formed a gear  93 . Inside of the casing K 3 , moreover, there is disposed an output shaft  94  which is in parallel with the intermediate shaft  85 . On this output shaft  94 , there are formed gears  95  and  96 . Moreover, the gear  93  and the gear  95  mesh with each other. 
     Inside of the casing K 3 , on the other hand, there is disposed a differential gears  97 , the ring gear  98  of which meshes with the gear  96 . The differential gears  97  is of the well-known type including the differential case, the pinion gear, the side gear and so on. To the output side of the differential gears  97 , there are connected right and left front drive shafts  99 . Each of these drive shafts  99  is exposed to the outside of the casing K 3 . The right and left (front) wheels are individually connected to those front drive shafts  99 . To the system of FIG. 8, there can also be applied the control system of FIG.  2 . In this case, the oil pressures to act on the clutch C 0  and the brakes B 0  and B 1  are controlled by the hydraulic control unit  45  shown in FIG.  2 . 
     Here will be described the corresponding relations between the construction shown in FIG.  8  and the invention. The second planetary gear mechanism  86  corresponds to the planetary gear mechanism of the invention. On the other hand, the input shaft  76 , the intermediate shaft  85 , the shaft  94 , the differential gears  97  and the front drive shaft  99  construct a route corresponding to the torque transmitting route of the invention. Moreover, the output shaft  87 , the connecting drum  92  and the intermediate shaft  85  construct a route corresponding to the torque adding route of the invention. 
     The controls on the system shown in FIG. 8 will be described with reference to the diagram of FIG.  9 . FIG. 9 is a diagram tabulating corresponding relations among the various drive patterns, the states of the frictional engagement elements and the drive/driven means. In the embodiment shown in FIG. 8, too, it is possible to make controls corresponding to the individual drive patterns such as the creep run, the ordinary start, the ordinary run, the regenerative brake and the backward run on the basis of the running state of the vehicle. The relations between these individual drive patterns and the running state of the vehicle are similar to those tabulated in the diagram of FIG.  3 . In FIG.  9 : “circle” symbols imply that the frictional engagement elements are applied; a “triangle” symbol imply that the frictional engagement element is applied when the vehicle is quickly started; and blanks imply that the frictional engagement elements are released. 
     First of all, when the creep run pattern is selected, the brake B 1  and the second one-way clutch F 2  are applied, but the other clutches and brakes are released. In short, the ring gear  89  is fixed. On the other hand, the clutch C 0  and the brake B 0  are released to block the torque transmitting route between the engine  1  and the continuously variable transmission  2 . If, in this state, the torque of the motor/generator  15  is transmitted to the sun gear  88 , the ring gear  89  functions as the reaction element so that the RPM of the sun gear  88  is decelerated with respect to the carrier  91 , and the torque of the carrier  91  is transmitted to the intermediate shaft  85 . In short, the second planetary gear mechanism  86  has a function as the so-called “transmission” to decelerate the intermediate shaft  85  with respect to the motor/generator  15 . 
     The torque of the intermediate shaft  85  is transmitted through the gears  93  and  95 , the output shaft  94  and the gear  96  to the differential gears  97 . Then, the torque, as transmitted to the differential gears  97 , is transmitted by the front drive shafts  99  to generate the driving force of the right and left wheels  33 . Thus, at the time of the creep run, the motor/generator  15  acts as the drive means for the vehicle. 
     When the ordinary start pattern is selected, on the other hand, the brake B 1 , the second one-way clutch F 2  and the clutch C 0  are applied, but the other clutches and brakes are released. When, in this state, the torque of the engine  1  is transmitted to the input shaft  76 , the sun gear  79  and the carrier  83  rotate together so that their torque is transmitted through the hollow shaft  84  to the continuously variable transmission  2 . The torque thus inputted to the continuously variable transmission  2  is transmitted through the drive-side pulley  6 , the belt  14  and the driven-side pulley  7  to the intermediate shaft  85 . Here, the control contents of the continuously variable transmission  2  are similar to those of the embodiment of FIG.  1 . 
     On the other hand, the second one-way clutch F 2  and the brake B 1  are applied, the torque of the motor/generator  15  is amplified and transmitted to the intermediate shaft  85  as at the control time of the creep run. As a result, the torque of the motor/generator  15  is added to the output torque of the continuously variable transmission  2  so that the summed torque is transmitted to the output shaft  94 . Thus, at the ordinary start time, the engine  1  and the motor/generator  15  are the drive means for the vehicle. 
     When the ordinary run pattern is selected, moreover, the brake B 1  and the clutch C 0  are applied, but the other clutches and brakes are released. Then, the torque of the engine  1  is inputted as at the ordinary start pattern time to the continuously variable transmission  2 , and the torque is outputted from the continuously variable transmission  2  and transmitted to the output shaft  94 . In this case, no torque is outputted from the motor/generator  15 , and only the engine  1  is the drive means for the vehicle. When the demand for the acceleration exceeds a predetermined value, on the contrary, the motor/generator  15  is driven so that its torque is transmitted to the ring gear  89  to apply the second one-way clutch F 2 . As a result, the ring gear  89  functions as the reaction element so that the torque of the motor/generator  15  is amplified and transmitted to the intermediate shaft  85 . In short, when the ordinary run pattern is selected, too, the engine  1  and the motor/generator  15  are the drive means for the vehicle like the case in which the ordinary start pattern is selected. 
     When the backward run pattern is selected, on the other hand, the brake B 0  is applied, but the other brakes and the clutches are released. When the torque of the engine  1  is transmitted to the input shaft  76 , therefore, the ring gear  82  functions as the reaction element so that the carrier  83  rotates in the opposite direction to the rotation at the forward run. Then, the transmission route of the torque outputted from the carrier  83  is similar to that at the ordinary start time, and the torque is transmitted to the wheels  33  to generate a driving force to move the vehicle backward. At this backward run time, the torque of the intermediate shaft  85  is also transmitted through the second planetary gear mechanism  86  to the motor/generator  15 . However, the brake B 1  is released so that the motor/generator motor/generator can be stopped. If the driving force of the motor/generator  15  is necessary, however, the first one-way clutch F 1  of the second planetary gear mechanism  86  is applied by rotating the motor/generator  15  opposite to the aforementioned direction to connect the motor/generator  15  and the intermediate shaft  85  directly. 
     When the regenerative brake pattern is selected, on the other hand, the brake B 1  is continuously applied by the hydraulic control unit  45 , but the other brakes and the clutches are released so that the motor/generator  15  acts as the power generator. On the other hand, the running inertia, as inputted from the wheels  33 , is transmitted through the differential gears  97  to the intermediate shaft  85 . 
     Then, the first one-way clutch F 1  is applied so that the ring gear  89 , the carrier  91  and the sun gear  88  are caused to rotate altogether by the torque of the intermediate shaft  85  to connect the intermediate shaft  85  and the output shaft  87  directly. Thus, the motive power is inputted from the intermediate shaft  85  to the motor/generator  15  so that the battery  50  is charged with the electric energy generated by the motor/generator  15 . Thus, when the regenerative brake pattern is selected, the motor/generator  15  acts as the driven means. As thus described, the one-way clutches F 1  and F 2  perform: a role to be applied, only when one rotary element rotates in a predetermined direction, to transmit the torque to the other rotary element; and a role to cause, when one rotary element rotates, the other rotary element to function as the reaction element. 
     According to the embodiment thus far described with reference to FIGS. 8 and 9, the torque of the motor/generator  15  is amplified by the second planetary gear mechanism  86  and transmitted to the output side of the continuously variable transmission  2 . As a result, the torque of the continuously variable transmission  2  and the torque of the motor/generator  15  are summed and transmitted to the wheels  33 . As a result, the torque to be transmitted from the engine  1  to the continuously variable transmission  2  is lower than that to be transmitted to the wheels  33 . In the embodiment of FIGS. 8 and 9, therefore, the power transmission efficiency and the durability of the continuously variable transmission  2  can also be improved for the same reasons as those of the embodiment of FIGS. 1 to  3 . 
     On the other hand, the torque of the motor/generator  15  is added to the torque outputted from the continuously variable transmission  2 . Even when the reduction ratio of the continuously variable transmission  2  is set so high as to make the motor/generator  15  compact, therefore, the RPM of the motor/generator  15  does not rise so high at a high-speed running time as to exceed the allowable value. As a result, the motor/generator  15  can be prevented from being overheated, to improve its own durability. 
     According to the embodiment shown in FIGS. 8 and 9, moreover, the first one-way clutch F 1  is applied/released by switching the controlled state of the motor/generator  15  between the electric motor (for the power running) and the power generator (for the regeneration). At the power running time and the regenerating time, it is possible to make the gear ratios different on the input side and the output side of the second planetary gear mechanism  86  (that is, to set a plurality of gear stages). As a result, the second planetary gear mechanism  86 , which is connected in the torque transmittable manner to the output shaft  30  so as to reduce the torque of the motor/generator  15 , can be switched between the decelerated state and the directly connected state without any control by a special control system, and neither the switching timing nor the oil pressure need be controlled. This can simplify the system and suppress the manufacture cost. 
     Although the invention has been described in connection with its specific embodiments, it should not be limited thereto. Therefore, the transmission in the invention may be exemplified by a toroidal (or traction) type continuously variable transmission, a hydraulic type continuously variable transmission in which the oil pressure is established by an input-side member to rotate an output-side member, or a gear type transmission. 
     On the other hand, the start clutch employed in the above specific embodiments may be replaced by a torque converter. 
     Here will be synthetically described the advantages to be obtained by the invention. 
     When the torque to satisfy a demand for the driving force for the vehicle is to be transmitted to the wheels, according to the invention, the torque to be transmitted from the output side of the transmission to the wheels can be increased or amplified by the functions of the second driving force source and the planetary gear mechanism. This makes it possible to reduce the torque to be inputted from the first driving force source to the transmission. As a result, the slippage between the members for transmitting the torque between the input side and the output side of the transmission can be suppressed to improve the power transmission efficiency and the durability of the transmission. 
     According to the invention, on the other hand, the torque to be transmitted from the output side of the transmission to the wheels can be increased or amplified by the functions of the second driving force source and the plurality of planetary gear units. As a result, the power transmission efficiency and the durability of the transmission can be improved, as described above. 
     According to the invention, moreover, the torque to be outputted from the transmission is transmitted through the first sun gear to the carrier. When the torque of the electric motor is transmitted to the second sun gear, moreover, this second sun gear functions as the reaction element so that the RPM of the first sun gear is decelerated and transmitted to the carrier. In response to a change in the demand for the driving force for the vehicle, therefore, the torque to be inputted from the first driving force source to the transmission can be reduced to improve the power transmission efficiency and the durability of the transmission, as described above. 
     According to the invention, still moreover, the torque to be outputted from the transmission is transmitted to the second sun gear. When the torque of the second driving force source is transmitted to the second ring gear, this second ring gear then functions as the reaction element so that the torque of the second sun gear is decelerated and transmitted to the second carrier. In response to a change in the demand for the driving force for the vehicle, therefore, the torque to be inputted from the first driving force source to the transmission can be reduced to improve the power transmission efficiency and the durability of the transmission, as described above. 
     According to the invention, moreover, the torque of the second driving force source is transmitted, after amplified, to the output side of the transmission so that the output torque of the transmission and the torque of the second driving force source are summed and transmitted to the wheels. In response to the change in the demand for the driving force for the vehicle, therefore, the torque to be inputted from the first driving force source to the transmission can be reduced to improve the power transmission efficiency and the durability of the transmission, as described above.