Abstract:
The present invention provide a power train of a hybrid vehicle that can be mounted in plug-in hybrid vehicles as well as environment-friendly vehicles, while reducing the cost and weight with less parts and a simple structure, ensuring good mounting characteristics in a vehicle, and improving fuel efficiency and power performance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is based on, and claims priority from, Korean Application Serial Number 10-2008-0121819, filed on Dec. 3, 2008, the disclosure of which is hereby incorporated by reference herein in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a power train of a hybrid vehicle, in more detail a power train arrangement of a hybrid vehicle that uses an engine, which is an internal combustion engine, and a motor generator driven by electricity as a power source providing driving force to a driving wheel. 
       BACKGROUND ART 
       [0003]    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. 
         [0004]    Further, hybrid vehicles do not produce exhaust gas from the engine when being driven only by a motor generator, which is recognized as an environment-friendly vehicle technology having advantages of improving fuel efficiency and reducing exhaust gas. 
         [0005]    Researches for reducing manufacturing costs, providing simpler structures, providing lighter and less parts, ensuring good mounting characteristics, and improving fuel efficiency and power performance have been continuously conducted. 
         [0006]    The information disclosed in this Background Art 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. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    Embodiments of the present invention provide a power train of a hybrid vehicle which can be mounted in common hybrid vehicles, which are environmental-friendly vehicles, and plug-in hybrid vehicles, while reducing the cost and weight with less parts and a simple structure, and improving fuel efficiency and power performance. 
         [0008]    In one aspect, the present invention provides a power train of a hybrid vehicle that comprises a first planetary gear set, a second planetary gear set, a first clutch, and a second clutch. The first planetary gear set is connected with an output element and a first motor generator. The second planetary gear set is aligned coaxially with the first planetary gear set and connected with the output element, an input element, and a second motor generator. The first clutch is configured to selectively fix a mode shift gear element of the first planetary gear set. The second clutch is configured to selectively connect the mode shift gear element of the first planetary gear set with a gear element of the second planetary gear set that is not connected with the second motor generator and the output element. 
         [0009]    In another aspect, the present invention provides a power train of a hybrid vehicle that comprises a first planetary gear set, a second planetary gear set, a first clutch, a second clutch, a third clutch, and a fourth clutch. The first planetary gear set is connected with an output element and a first motor generator. The second planetary gear set is connected with an input element and a second motor generator. The first clutch is connected with a gear element of the first planetary gear set that is not connected with the output element. The second clutch is connected with a gear element of the second planetary gear set that is not connected with the second motor generator and the output element. The third clutch is connected with a gear element of the second planetary gear set that is not connected with the output element. The fourth clutch is connected with the first planetary gear set and the second planetary gear set. 
         [0010]    The above and other features and advantages of the present invention will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated in and form a part of this specification, and the following Detailed Description, which together serve to explain by way of example the principles of the present invention. 
         [0011]    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 
         [0012]    For better understanding of the nature and objects of the present invention, reference should be made to the following detailed description with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a diagram illustrating an embodiment of a power train of a hybrid vehicle according to the present invention; 
           [0014]      FIG. 2  is a diagram illustrating another embodiment of a power train of a hybrid vehicle according to the present invention; 
           [0015]      FIG. 3  is a diagram illustrating still another embodiment of a power train of a hybrid vehicle according to the present invention; and 
           [0016]      FIG. 4  is an operation table of clutches that are operated for each driving mode in the power trains of  FIGS. 1-3 . 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0017]    Referring to  FIG. 1 , a power train of a hybrid vehicle according to an embodiment of the present invention includes a first planetary gear set  3 , a second planetary gear set  11 , a first clutch  13 , and a second clutch  13 . 
         [0018]    The first planetary gear set  3  is connected with an output element  5  and a first motor generator  1 . The second planetary gear set  11  is disposed coaxially with the first planetary gear set  3  and connected with the output element  5 , an input element  7 , and a second motor generator  9 . The first clutch  13  is provided to selectively fix a mode shift gear element of the first planetary gear set  3 . The second clutch  15  is provided to selectively connect the mode shift gear element of first planetary gear set  3  with an element of the second planetary gear set  11  that is connected neither with the second motor generator  9  nor with the output element  5 . 
         [0019]    According to another embodiment of the present invention, as shown in  FIG. 2 , in addition to the configuration of the embodiment shown in  FIG. 1 , the power train may further include a third clutch  17  and a fourth clutch  19 . 
         [0020]    The third clutch  17  is disposed to selectively fix an element of the second planetary gear set  11  which is connected with the second motor generator  9 . The fourth clutch  19  is provided to selectively connect the element of the second planetary gear set  11  that is connected neither with the second motor generator  9  nor with the output element  5  with an element of the first planetary gear set  3  that is connected with the first motor generator  1 . 
         [0021]    According to still another embodiment of the present invention, as shown in  FIG. 3 , Further, in addition to configuration of the embodiment shown in  FIG. 2 , the power train may further include a fifth clutch  2  that is provided to selectively connect the input element  7  with an element of the second planetary gear set  11 . 
         [0022]    In all of the embodiments shown in  FIGS. 1 to 3 , the output element  5  is connected with a carrier CR 1  of the first planetary gear set  3  and a ring gear RG 2  of the second planetary gear set  11  and the mode shift gear element of the first planetary gear set  3  is a ring gear RG 1 . 
         [0023]    The first motor generator  1  is connected to a sun gear SG 1  of the first planetary gear set  3 , the output element  5  is connected to the carrier CR 1  of the first planetary gear set  3 , and the first clutch  13  and second clutch  15  are connected to the ring gear RG 1  of the first planetary gear set  3 . Suitably, the output element  5  may be connected to the ring gear RG 1  of the first planetary gear set  3  and the first clutch  13  and the second clutch  15  may be connected to the carrier CR 1  of the first planetary gear set  3 , while the first motor generator  1  is connected to the sun gear SG 1 . 
         [0024]    The second motor generator  9  is connected to a sun gear SG 2  of the second planetary gear set  11 , the output element  5  is connected to the ring gear RG 2  of the second planetary gear set  11 , and the input element  7  and the second clutch  15  are connected to a carrier CR 2  of the second planetary gear set  11 . Suitably, the configuration may be implemented in an inverse way, e.g., that the output element  5  may be connected to the carrier CR 2  of the second planetary gear set  11  and the input element  7  and the second clutch  15  may be connected to the ring gear RG 2  of the second planetary gear set  11  while the second motor generator  9  is connected to the sun gear SG 2  of the second planetary gear set  11 . 
         [0025]    The input element  7  may be an engine and the output element  5  may be a differential connected to driving wheels of the vehicle. 
         [0026]    The operation of the power trains according to the present invention is described with the embodiment shown in  FIG. 3  and the operation table shown in  FIG. 4 . The power train according to the embodiment can be operated in various modes: EV 1 , EV 1 ′, EV 2 , EV 3 , HEV 1 , HEV 2 , ENG 1 , ENG 2 , and ENG 3 . 
         [0027]    The EV 1  mode is implemented by fixing the ring gear RG 1  by engaging the first clutch  13  and generating torque from the first motor generator  1  connected with the first sun gear SG 1 . In this mode, an under-drive shift stage is achieved in which the driving force outputted from the first motor generator  1  is reduced in accordance with the shift ratio of the first planetary gear set  3  and outputted through the output element  5  connected to the first carrier CR 1 . 
         [0028]    The EV 1 ′ mode is a mode for maximizing driving force of a vehicle using the first motor generator  1  and the second motor generator  9  as motors in case of rapid acceleration in an EV mode traveling. That is, in this mode, the ring gear RG 1  is connected with the carrier CR 2  by additionally engaging the second clutch  15  such that the engine is fixed with the ring gear RG 1  and the carrier CR 2 , and the first motor generator  1  and the second motor generator  9  both provide power. When two motor generators generate power, torque exerted in the output element  5  is [gear ratio of the first planetary gear set+1]*[torque of the first motor generator]+[gear ratio of the second planetary gear set  11 ]*[torque of the second motor generator]. 
         [0029]    The EV 2  mode is a mode for connecting the ring gear RG 1  with the carrier CR 2  such that the first and second planetary gear sets are integrally operated by engaging the second clutch  15 , and for driving only the first motor generator  1  as a motor while fixing the sun gear SG 2  by engaging the third clutch  17 . In this mode, the rotational velocity of the first motor generator  1  connected to the sun gear SG 1  is higher than the carrier CR 1  and the ring gear RG 2 , which are connected with the output shaft, but it is lower than that of the EV 1  mode. 
         [0030]    The EV 3  mode is a driving mode at a transmission ratio of 1.0 which is achieved by rotating all of the gear elements of the first planetary gear set  3  and the second planetary gear set  11  at the same velocity by engaging the second clutch  15  and the fourth clutch  19 . In this mode, the torque of the first motor generator  1  is entirely transmitted to the output shaft of the transmission. As a result, the transmission ratio provided by the power train in the EV modes includes two under-drive transmission ratios and one transmission ratio of 1.0. 
         [0031]    In the EV modes, since the fifth clutch  21  is disengaged and the gear elements of the second planetary gear set  11  are disconnected with the engine, the operation of the second planetary gear set  11  and the first planetary gear set  3  is free from the velocity of the engine. By contrast, in HEV modes, since the fifth clutch  21  is engaged, power of the engine is transmitted to the driving wheels through second planetary gear set  11 . 
         [0032]    The HEV 1  mode is an input split mode, which is implemented by engaging the fifth clutch  21  in the EV 1  mode. That is, the first motor generator  1  connected with the sun gear SG 1  generates output torque together with the engine while operating as a motor and the second motor generator  9  connected with the sun gear SG 2  implements electronic continuously variable transmission by changing the velocity of the engine connected with the carrier CR 2 . 
         [0033]    The HEV 2  mode integrally operates the two planetary gear sets together with the carrier CR 1  and the ring gear RG 2 , which are always connected through the output shaft, by engaging the second clutch  15  such that the ring gear RG 1  is connected with the carrier CR 2  in the HEV  1  mode. In this operation, not only the two motor generators are electrically connected, but they operate in a compound split mode that should satisfy the velocity-torque relation of the planetary gear sets. 
         [0034]    The ENG 1  mode achieves an under-drive shift stage by engaging the first clutch  13  in which the sun gear SG 1  connected with the first motor generator  1  rotates at high velocity with respect to the carrier CR 1  connected with the output shaft, and then engaging fourth clutch  19  in which the carrier CR 2  connected with the engine is connected with the sun gear SG 1 , thereby allowing the engine to achieve an under-drive shift stage with respect to the output shaft. In this operation, the vehicle can be driven by the engine torque through the second planetary gear set, even though both motor generators do not generate torque. 
         [0035]    The ENG 2  mode is a driving mode at a transmission ratio of 1.0 in which all of the gear elements of the two planetary gear sets rotate at the same velocity by engaging the second clutch  15  and the fourth clutch  19 . Accordingly, only gear elements of the second planetary gear set  11  transmit torque and the engine torque is entirely transmitted to the output shaft of the transmission. 
         [0036]    The ENG 3  mode is a mode that achieves an over-drive shift ratio by engaging the third clutch  17  such that sun gear SG 2  is fixed, in which the carrier CR 2  connected with the engine rotates at a low velocity with respect to the ring gear RG 2  connected to the output shaft. In this operation, since the first motor generator  1  does not transmit torque, all of the gear elements of the first planetary gear set  3  do not transmit torque and a shift stage is achieved only by the second planetary gear set  11 . 
         [0037]    As a result, the transmission ratio provided by the power train in the ENG modes includes one under-drive transmission ratio, one transmission ratio of 1.0, and one over-drive transmission ratio. 
         [0038]    The above-described power train provides two HEV modes of the input split and the compound split modes, and provides an engine driving mode of three transmission ratios for improving fuel efficiency under a high-speed cruising condition. 
         [0039]    Further, the power train provides functions suitable for plug-in hybrid vehicles or fuel cell vehicles. That is, providing a plurality of shift stages in the EV modes will allow the motor to be driven with high efficiency since these vehicles have longer traveling distance in an electric vehicle mode. 
         [0040]    Further, as in the EV 1 ′ mode, since two motor generators provide a high-torque under-drive transmission ratio where they all operate as motors, it is possible to satisfy when a driver needs high level of acceleration. 
         [0041]    Meanwhile, as described above, since the present invention can provide traveling modes of four EV modes, two HEV modes, and three ENG modes, using two planetary gear sets and maximum five clutch/brake members, as compared with other power trains in the related art, the present invention reduces the cost and the weight by reducing the number of parts, and has a technical advantage in terms of mounting characteristic in a vehicle, power performance, and fuel efficiency. 
         [0042]    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.