Abstract:
The present invention provides a power train for a hybrid vehicle that allows for multiple mode driving, which is combined with a way of driving at a fixed gear ratio such as the shift stages of a common transmission, and high-efficiency driving, thereby improving fuel efficiency of the vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to Korean Patent Application Number 10-2009-0035352 filed Apr. 23, 2009, the entire contents of which application is incorporated herein for all purposes by this reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to a power train for a hybrid vehicle, in more detail a technology for transmitting power from power sources to the driving wheels in a hybrid vehicle equipped with two or more different power sources, including an internal combustion engine. 
         [0004]    2. Related Art 
         [0005]    Hybrid vehicles using an engine and a motor generator improve fuel efficiency of the vehicles by achieving functions of idle stop and regenerative braking, on the basis of a technology of driving the vehicles at low velocity by using power from the motor generator having relatively excellent low-velocity torque characteristics and driving the vehicles at high velocity by using power from the engine having relatively excellent high-velocity characteristics. 
         [0006]    Further, hybrid vehicles do not produce exhaust gas from the engine when being driven only by a motor generator, which is recognized as an environmental-friendly vehicle technology having advantages of improving fuel efficiency and reducing exhaust gas. 
         [0007]    A power split type device has been known in the field of power trains for hybrid vehicles, which is classified into a single mode way and a multiple mode way. The single mode way does not need an operational element for shift control, such as a clutch or a brake, but the efficiency decreases in a high-velocity traveling, such that fuel efficiency is low and an additional torque amplifier is required to be applied to large-sized vehicles. 
         [0008]    On the other hand, the multiple mode way can be designed to be able to ensure efficiency in high-velocity traveling and amplify torque by itself in accordance with the configuration, such that it can be applied to medium- and large-sized vehicles. 
         [0009]    The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
       BRIEF SUMMARY OF THE DISCLOSURE 
       [0010]    Various aspects of the present invention are directed to provide a power train for a hybrid vehicle that allows for multiple mode driving, which is combined with a way of driving at a fixed gear ratio such as the shift stages of a common transmission, and high-efficiency driving, thereby improving fuel efficiency of the vehicle. 
         [0011]    In one aspect, the present invention provides a power train for a hybrid vehicle comprising: a first planetary gear set including rotary elements; a second planetary gear set including rotary elements at least one of which is connected with at least one of the rotary elements of the first planetary gear set; a first clutch that is configured to connect/disconnect one of the rotary elements of the first planetary gear set with/from one of the rotary elements of the second planetary gear set; and a first brake that is configured to restrain rotation of one rotary element of the second planetary gear set. In addition, at least two or more independent power sources and an output element are connected to some of the rotary elements of the first planetary gear set and the second planetary gear set. 
         [0012]    Preferably, the power source may include an engine and a first motor generator that are connected to the first planetary gear set, and a second motor generator that is connected to the second planetary gear set. The output element may be connected to the second planetary gear set. In this case, the first planetary gear set and the second planetary gear set, and the first motor generator and the second motor generator may be coaxially arranged. Further, one rotary element of the first planetary gear set may be directly connected with one rotary element of the second planetary gear set, and the first clutch may be connected with one of the other rotary elements of the first planetary gear set and one of the other rotary elements of the second planetary gear set. In this case, preferably, the engine may be connected with the rotary element, which is connected to the first clutch, of the first planetary gear set, the first clutch may be connected to the rotary element, which is connected to the first brake, of the second planetary gear set, and the output element may be connected to one rotary element, which is not connected with the first planetary gear set and the first clutch, of the second planetary gear set. Further, the first motor generator may, suitably, be connected with the rotary element, which is not connected with the first clutch and the rotary elements of the second planetary gear set, of the first planetary gear set, and the second motor generator may, suitably, be connected to the rotary element, which is connected with the first clutch, of the second planetary gear set. 
         [0013]    Preferably, a first ring gear of the first planetary gear set and a second sun gear of the second planetary gear set may be directly connected, the first clutch may be configured to connect/disconnect a first carrier of the first planetary gear set with/from a second ring gear of the second planetary gear set, the engine may be connected to the first carrier of the first planetary gear set, the first motor generator may be connected to a first sun gear of the first planetary gear set, the second motor generator may be connected to the second sun gear of the second planetary gear set, the first brake may be disposed to restrain rotation of the second ring gear of the second planetary gear set, and the output element may be connected to a second carrier of the second planetary gear set. 
         [0014]    Preferably, the power train may further comprise a second brake that is configured to restrain rotation of the rotary element, which is connected with the second motor generator, of the second planetary gear set. In this case, suitably, the power train may further comprise a third brake that is configured to restrain rotation of the rotary element, which is connected with the first motor generator, of the first planetary gear set. 
         [0015]    Preferably, the power train may further comprise a third clutch that is configured to connect/disconnect the rotary elements, which are connected with the engine and the first motor generator, of the first planetary gear set. In this case, it may further comprise a second brake that is provided to restrain rotation of the rotary element, which is connected with the second motor generator, of the second planetary gear set; and a third brake that is provided to restrain rotation of the rotary element, which is connected with the first motor generator, of the first planetary gear set. 
         [0016]    In another aspect, the present invention provides a power train for a hybrid vehicle, comprising: a first planetary gear set that has three rotary elements; a second planetary gear set that has three rotary elements two of which are connected with two of the rotary elements of the first planetary gear set so as to connect/disconnect power transmission therebetween; a first brake that is connected to one of the rotary elements of the second planetary gear set that are connected with the rotary elements of the first planetary gear set, so as to restrain rotation of the rotary elements; and a second brake that is connected to another one of the rotary elements of the second planetary gear set that are connected with the rotary elements of the first planetary gear set, so as to restrain rotation of the rotary elements. In addition, at least two or more independent power sources and an output element are connected to the rotary elements of the first planetary gear set and the second planetary gear set. 
         [0017]    Preferably, the power source may include an engine and a first motor generator that are connected to the first planetary gear set; and a second motor generator that is connected to the second planetary gear set. The output element may be connected to the second planetary gear set. In this case, a first clutch and a second clutch may be disposed between the pairs of rotary elements of the first planetary gear set and the second planetary gear set, respectively, the engine may be connected to the rotary element, which is connected to the first clutch, of the first planetary gear set, and the output element may be connected to the rotary element, which is not connected with any of the rotary elements of the first planetary gear set, of the second planetary gear set. 
         [0018]    Preferably, a first clutch may be disposed to connect/disconnect a first carrier of the first planetary gear set with/from a second ring gear of the second planetary gear set, and a second clutch may be disposed to connect/disconnect a first ring gear of the first planetary gear set and a second sun gear of the second planetary gear set. In this case, the first brake and the second brake may be configured to restrain rotation of rotary elements, which are connected to the first planetary gear set through the first clutch and the second clutch, of the second planetary gear set. The power train may, suitably, further comprise a third clutch that is disposed to connect/disconnect the rotary elements, which are connected with the first motor generator and the engine, of the first planetary gear set. The power train may, also suitably, further comprise a third brake that is connected to connect/disconnect rotation of the rotary element, which is connected with the first motor generator, of the first planetary gear set. The power train may, also suitably, further comprise a third clutch that is configured to connect/disconnect the rotary element, which is connected with the engine, of the first planetary gear set with/from the rotary element, which is connected with the second motor generator, of the second planetary gear set. 
         [0019]    The present invention allows for multiple mode driving, which is combined with a way of driving at a fixed gear ratio such as the shift stages of a common transmission, and high-efficiency driving within the entire shift ratio of a vehicle, thereby improving fuel efficiency of the vehicle. 
         [0020]    The above and other features and advantages will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention. 
         [0021]    It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a diagram illustrating the structure and an operation mode table of a power train for a hybrid vehicle according to a first embodiment of the present invention. 
           [0023]      FIG. 2  is a lever analysis diagram of the power train of  FIG. 1 . 
           [0024]      FIG. 3  is a diagram illustrating a power train with modification added to the power train of  FIG. 1 . 
           [0025]      FIG. 4  is a diagram illustrating the structure and an operation mode table of a power train for a hybrid vehicle according to a second embodiment of the present invention. 
           [0026]      FIG. 5  is a diagram illustrating the structure and an operation mode table of a power train for a hybrid vehicle according to a third embodiment of the present invention. 
           [0027]      FIG. 6  is a diagram illustrating the structure and an operation mode table of a power train for a hybrid vehicle according to a fourth embodiment of the present invention. 
           [0028]      FIG. 7  is a diagram illustrating the structure, an operation mode table, and a lever analysis diagram of a power train for a hybrid vehicle according to a fifth embodiment of the present invention. 
           [0029]      FIG. 8  is a diagram illustrating the structure and an operation mode table of a power train for a hybrid vehicle according to a sixth embodiment of the present invention. 
           [0030]      FIG. 9  is a diagram illustrating the structure and an operation mode table of a power train for a hybrid vehicle according to a seventh embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0031]    Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0032]    Referring to  FIGS. 1 and 2 , a power train for a hybrid vehicle in accordance with a first embodiment of the present invention includes: a first planetary gear set PG 1  that has rotary elements; a second planetary gear set PG 2  that has rotary elements at least one of which is connected with at least one of the rotary elements of the first planetary gear set PG 1 ; a first clutch CL 1  that is configured to connect/disconnect the rotary elements of the first planetary gear set PG 1  with/from the rotary elements of the second planetary gear set PG 2 ; and a first brake BK 1  that is configured to restrain rotation of one rotary element of the second planetary gear set PG 2 , in which at least two or more independent power sources and an output element OUT are connected to the rotary elements of the first planetary gear set PG 1  and/or the second planetary gear set PG 2 . 
         [0033]    The power source includes an engine E/G and a first motor generator MG 1  that are connected to the first planetary gear set PG 1 , and a second motor generator MG 2  that is connected to the second planetary gear set PG 2 , and output element OUT is connected to the second planetary gear set PG 2 . The first planetary gear set PG 1  and the second planetary gear set PG 2 , and the first motor generator MG 1  of and the second motor generator MG 2  are coaxially arranged. 
         [0034]    One rotary element of the first planetary gear set PG 1  is directly connected with one rotary element of the second planetary gear set PG 2 , and the first clutch CL 1  is connected with one of the other rotary elements of the first planetary gear set PG 1  and one of the other rotary elements of the second planetary gear set PG 2 . 
         [0035]    The engine E/G is connected with the rotary element, which is connected to the first clutch CL 1 , of the first planetary gear set, the first clutch CL 1  is connected to the rotary element, which is connected to the first brake BK 1 , of the second planetary gear set PG 2 , and the output element OUT is connected to one rotary element, which is not connected with the first planetary gear set PG 1  and the first clutch CL 1 , of the second planetary gear set PG 2 . 
         [0036]    The first motor generator MG 1  is connected with the rotary element, which is not connected with the first clutch CL 1  and the rotary elements of the second planetary gear set PG 2 , of the first planetary gear set PG 1 . The second motor generator MG 2  is connected to the rotary element, which is not connected with the first clutch CL 1  and the output element OUT, of the second planetary gear set PG 2 . 
         [0037]    A second brake BK 2  is provided to restrain rotation of the rotary element, which is connected with the second motor generator MG 2 , of the second planetary gear set PG 2 . 
         [0038]    In an embodiment, as shown in  FIGS. 1 and 2 , a first ring gear R 1  of the first planetary gear set PG 1  and a second sun gear S 2  of the second planetary gear set PG 2  are directly connected, the first clutch CL 1  is disposed to connect/disconnect a first carrier C 1  of the first planetary gear set PG 1  with/from a second ring gear R 2  of the second planetary gear set PG 2 , the engine E/G is connected to the first carrier C 1  of the first planetary gear set PG 1 , the first motor generator MG 1  is connected to a first sun gear S 1  of the first planetary gear set PG 1 , the second motor generator MG 2  is connected to the second sun gear S 2  of the second planetary gear set PG 2 , the first brake BK 1  is disposed to restrain rotation of the second ring gear R 2  of the second planetary gear set PG 2 , the output element OUT is connected to a second carrier C 2  of the second planetary gear set PG 2 , and the second brake BK 2  is connected to the second sun gear S 2  of the second planetary gear set PG 2 . 
         [0039]    The power train for a hybrid vehicle having the above configuration can be operated in an electrical vehicle (EV) mode, a complex split mode, and an input split mode as described in the table of  FIG. 1 . It can also be operated in a fixed gear ratio mode of one stage, which can achieve a predetermined shift ratio while only the engine E/G is operated. 
         [0040]    More specifically, the EV mode can be achieved by activating only the second motor generator MG 2  with the first brake BK 1  engaged, or activating both the first motor generator MG 1  and the second motor generator MG 2  with the first brake BK 1  operated and the first clutch CL 1  engaged. 
         [0041]    The complex split mode can be achieved by engaging only the first clutch CL 1 , in which both of the first motor generator MG 1  and the second motor generator MG 2  are connected to the engine E/G (an input element) and the output element OUT through the first planetary gear set PG 1  and the second planetary gear set PG 2 . 
         [0042]    The input split mode can be achieved by engaging only the first brake BK 1 , in which the second ring gear R 2  is fixed and the output element OUT connected to the second carrier C 2  is controlled at a predetermined shift ratio by activating the second motor generator MG 2  connected to the second sun gear S 2 . 
         [0043]    The first stage fixed gear ratio can be achieved by engaging the first clutch CL 1  and the second brake BK 2 . In this mode, the driving force outputted from the engine E/G is reduced in accordance with the shift ratio of the second planetary gear set PG 2  and outputted through the output element OUT connected to the second carrier C 2 . 
         [0044]      FIG. 3  shows a modified example of the power train of  FIGS. 1 and 2 , in which the second brake BK 2  of the power train of  FIGS. 1 and 2  is omitted. Accordingly, the power train of  FIG. 3  can achieve all the modes except for the first stage fixed gear ratio mode involving operation of the second brake BK 2 . 
         [0045]    In accordance with a second embodiment, as shown  FIG. 4 , a third brake BK 3  that is configured to restrain rotation of the rotary element, which is connected with the first motor generator MG 1 , of the first planetary gear set PG 1  is added to the power train according to the first embodiment shown in  FIG. 1 . 
         [0046]    Preferably, the third brake BK 3  may be connected to the first sun gear S 1  of the first planetary gear set PG 1  so as to restrain rotation of the first sun gear S 1 . 
         [0047]    The operation modes of the power train according to the second embodiment are the same as those of the power train according to the first embodiment, except that the power train according to the second embodiment can be operated in the first, second, and third stage fixed gear ratio modes. As the second stage fixed gear ratio mode of the power train according to the second embodiment is achieved by the same way as the first embodiment, the first and third stage fixed gear ratio modes are described herein below. 
         [0048]    The first fixed gear ratio mode of the power train according to the second embodiment is achieved by engaging the first brake BK 1  and the third brake BK 3 . In this mode, as the first sun gear S 1  is fixed by the third brake BK 3 , the power of the engine E/G is increased and transmitted to the first ring gear R 1  in accordance with the fixed gear ratio of the first planetary gear set PG 1 , and then the power drives the second sun gear S 2  integrally connected with the first ring gear R 1 . The second ring gear R 2  of the second planetary gear set PG 2  is fixed by the first brake BK 1 . As a result, the rotational force of the second sun gear S 2  is reduced by the fixed gear ratio of the second planetary gear set PG 2  and outputted to the output element OUT through the second carrier C 2 . 
         [0049]    The third stage fixed gear ratio is achieved by engaging the first clutch CL 1  and the third brake BK 3 . In this mode, the power output from the engine E/G is transmitted to the second ring gear R 2  of the second planetary gear set PG 2  and then increased and outputted to the second carrier C 2 . 
         [0050]    In accordance with a third embodiment, as shown  FIG. 5 , a third clutch CL 3  is added to and the second brake BK 2  is removed from the power train according to the first embodiment shown in  FIG. 1 . 
         [0051]    Preferably, the third clutch CL 3  may be disposed to connect/disconnect the rotary elements, which are connected with the engine E/G and the first motor generator MG 1 , of the first planetary gear set PG 1 . 
         [0052]    The operation modes of the power train according to the third embodiment are the same as those of the power train according to the first embodiment, except that the first and second stage fixed gear ratio modes are achieved in a different way. 
         [0053]    That is, the first fixed gear ratio mode is achieved by engaging the first brake BK 1  and the third clutch CL 3 . In this mode, as the third clutch CL 3  is engaged, the first planetary gear set PG 1  rotates as one unit together with the second sun gear S 2  of the second planetary gear set PG 2 . In this operation, since the first brake BK 1  is engaged, the power from the engine E/G is directly transmitted to the second sun gear S 2  of the second planetary gear set PG 2  and reduced by the fixed gear ratio of the second planetary gear set PG 2 , and then outputted to the output element OUT through the second carrier C 2 . 
         [0054]    The second fixed gear ratio mode is achieved by engaging the first clutch CL 1  and the third clutch CL 3 . In this mode, the first planetary gear set PG 1  operates as one unit by the engagement of the third clutch CL 3  and two pairs of the rotary elements of the first planetary gear set PG 1  and the second planetary gear set PG 2  are directly connected with each other by the engagement of the first clutch CL 1 . As a result, both of the first planetary gear set PG 1  and the second planetary gear set PG 2  rotate as one unit, such that the power from the engine E/G is outputted at a shift ratio of 1:1 to the output element OUT. 
         [0055]    In accordance with a fourth embodiment, as shown  FIG. 6 , a third clutch CL 3  and a third brake BK 2  are added to the power train according to the first embodiment shown in  FIG. 1 . 
         [0056]    Preferably, the third clutch CL 3  may be provided to connect/disconnect two elements of first planetary gear set PG 1  and the third brake BK 3  may be provided to restrain rotation of the rotary element, which is connected with the first motor generator MG 1 , of the first planetary gear set PG 1 . 
         [0057]    The operation modes of the power train according to the fourth embodiment are the same as those of the power train according to the first embodiment, except that the power train according to the four embodiment can be operated in the first, second, third, fourth, and fifth stage fixed gear ratio modes. 
         [0058]    The first stage fixed gear ratio mode of the power train according to the fourth embodiment is achieved by engaging the first brake BK 1  and the third clutch C 3 , which is the same as the first stage fixed gear ratio mode of the power train according to the third embodiment of  FIG. 5 . The second stage fixed gear ratio mode is achieved by engaging the first brake BK 1  and the third brake BK 3 , which is the same as the first stage fixed gear ratio mode of the power train according to the second embodiment of  FIG. 4 . The third stage fixed gear ratio mode is achieved by engaging the first clutch CL 1  and the second brake BK 2 , which is the same as the first stage fixed gear ratio mode of the power train according to the first embodiment of  FIG. 1 . The fourth stage fixed gear ratio mode is achieved by engaging the first clutch CL 1  and the third clutch CL 3 , which is the same as the second stage fixed gear ratio mode of the power train according to the third embodiment of  FIG. 5 . The fifth stage fixed gear ratio mode is achieved by engaging the first clutch CL 1  and the third brake BK 3 , which is the same as the third stage fixed gear ratio mode of the power train according to the second embodiment of  FIG. 4 . 
         [0059]      FIGS. 7 to 9  illustrate the power trains according to fifth to seventh embodiments of the present invention. These power trains have a common structure as follows. That is, the power trains include a first planetary gear set PG 1  having rotary elements and a second planetary gear set PG 2  having rotary elements. At least two pairs of the rotary elements of the first and second planetary gear sets PG 1  and PG 2  connect/disconnect power transmission therebetween. The power trains further include a first brake BK 1  and a second brake BK 2  that are respectively connected to the rotary elements, which are connected with the first planetary gear set PG 1 , of the second planetary gear set PG 2  to restrain rotation of the rotary elements. At least two or more independent power sources and an output element OUT are connected to the rotary elements of the first planetary gear set PG 1  and the second planetary gear set PG 2 . 
         [0060]    The power source includes an engine E/G and a first motor generator MG 1  that are connected to the first planetary gear set PG 1 , and a second motor generator MG 2  that is connected to second planetary gear set PG 2 . The output element OUT is connected to the second planetary gear set PG 2 . 
         [0061]    A first clutch CL 1  and a second clutch CL 2  are disposed between the pairs of the rotary elements of the first planetary gear set PG 1  and the second planetary gear set PG 2 , respectively. The engine E/G is connected to the rotary element, which is connected to the first clutch CL 1 , of the first planetary gear set PG 1 . The output element OUT is connected to the rotary element, which is not connected with the rotary elements of the first planetary gear set PG 1 , of the second planetary gear set PG 2 . 
         [0062]    Preferably, the first clutch CL 1  is disposed to connect/disconnect a first carrier C 1  of the first planetary gear set PG 1  with/from a second ring gear R 2  of the second planetary gear set PG 2 . The second clutch CL 2  is disposed to connect/disconnect a first ring gear R 1  of the first planetary gear set PG 1  and a second sun gear S 2  of the second planetary gear set PG 2 . 
         [0063]    Further, a first brake BK 1  and a second brake BK 2  configured to restrain rotation of the rotary elements, which are connected to the first planetary gear set PG 1  through the first clutch CL 1  and the second clutch CL 2 , of the second planetary gear set PG 2  are provided. 
         [0064]    The power train in accordance with a fifth embodiment, as shown  FIG. 7 , further includes a third clutch CL 3  that is disposed to connect/disconnect the rotary elements, which are connected with first motor generator MG 1  and the engine E/G, of the first planetary gear set PG 1 . 
         [0065]    As shown in the operation mode table of  FIG. 7 , the power train in accordance with this embodiment can be operated in an EV mode, a complex split mode, an output split mode, an input split mode, and first to third stage fixed gear ratio modes. 
         [0066]    The power train in accordance with a sixth embodiment, as shown  FIG. 8 , further includes a third brake BK 3  that is connected to connect/disconnect rotation of the rotary element, which is connected with the first motor generator MG 1 , of the first planetary gear set PG 1 . 
         [0067]    As shown in the operation mode table of  FIG. 8 , the power train in accordance with this embodiment can be operated in an EV mode, a complex split mode, an input split mode, and first to third stage fixed gear ratio modes. 
         [0068]    The power train in accordance with a seventh embodiment, as shown  FIG. 9 , further includes a third clutch CL 3  that is provided to connect/disconnect the rotary element, which is connected with the engine E/G, of the first planetary gear set PG 1  with/from the rotary element, which is connected with the second motor generator MG 2 , of the second planetary gear set PG 2 . 
         [0069]    As shown in the operation mode table of  FIG. 9 , the power train in accordance with this embodiment can be operated in an EV mode, a complex split mode, an input split mode, and first to fifth stage fixed gear ratio modes. 
         [0070]    On the other hand, describing the present invention in another way, a hybrid power train has two different power sources, including an engine, in which a first planetary gear set is composed of three rotary elements, a second planetary gear set is composed of three rotary elements, the first rotary element of the first planetary gear set is connected with an input element, the first rotary element of the second planetary gear set is connected with an output element, a first motor generator is connected to the second rotary element of the first planetary gear set, a second motor generator is connected to the second rotary element of the second planetary gear set, the second rotary element of the second planetary gear set and the third rotary element of the first planetary gear set are permanently or selectively connected, such that first power transmission is performed by selectively stopping the third rotary element of the second planetary gear set and second power transmission is performed by selectively connecting the third rotary element of the second planetary gear set with the first rotary element of the first planetary gear set. 
         [0071]    In this configuration, third power transmission can be performed by providing a clutch that can selectively transmit power from the input element to the second rotary element of the second planetary gear set. 
         [0072]    Further, a third brake is installed to the rotary element connected to the first motor generator and a second brake is installed to the rotary element connected to the second motor generator such that three or more fixed gear ratio modes are achieved by selectively operating the clutches and the brakes. 
         [0073]    The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.