Abstract:
A transmission for a vehicle employs parts as few as possible to provide forward 11-speed and reverse 1-speed gear ratios while having a relatively simple configuration, thereby allowing the operational state of an engine connected to the transmission to be in an optimal state. Thus, the transmission makes it possible to improve fuel efficiency and secure smooth driving performance of the vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2011-0095034, filed on Sep. 21, 2011, the entire contents of which is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates, in general, to a transmission for a vehicle, and, more particularly, to a structure of a transmission capable of realizing forward 11-speed and reverse 1-speed gear ratios. 
     2. Description of Related Art 
     Vehicles are equipped with a transmission so as to able to supply power generated from a power source such as an engine to drive wheels at the proper rotational speed and torque converted depending on driving conditions. 
     Such a transmission generally provides a plurality of gear ratios from a maximum gear ratio for meeting maximum hill-climbing capability to a minimum gear ratio for obtaining the highest speed of a vehicle. In theory, the greater the number of gear ratios, the more advantageous it is to secure the optimal driving point of the engine, so that it is possible to contribute to improving the fuel efficiency of the vehicle. 
     For reference, the prior art document, Korean Unexamined Patent Application Publication No. 10-2010-0097706, discloses a structure of a transmission capable of realizing forward 10-speed and reverse 2-speed gear ratios. 
     The information disclosed in this Background of the Invention 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 
     Various aspects of the present invention are directed to providing a transmission for a vehicle, which employs parts as few as possible to provide forward 11-speed and reverse 1-speed gear ratios along with relatively simple configuration, thereby allowing an engine connected thereto to be operated in an optimum state, and thus making it possible to improve fuel efficiency and to secure smooth driving performance in the vehicle. 
     In an aspect of the present invention, a transmission for a vehicle may include a first complex planetary gear train in which a first planetary gear train and a second planetary gear train are coupled to each other, a second complex planetary gear train in which a third planetary gear train and a fourth planetary gear train are coupled to each other, and which at least one rotational element of the second complex planetary gear train is connected with at least a rotational element of the first complex planetary gear train, an input shaft which is permanently connected to at least one rotational element of the first complex planetary gear train and is selectively connected to at least one rotational element of the first complex planetary gear train and at least a rotational element of the second complex planetary gear train, an output shaft which is connected to a rotational element of the second complex planetary gear train, first and second brakes which lock at least two rotational elements of the first complex planetary gear train, a third brake which locks a rotational element of the second complex planetary gear train, and a first clutch which selectively connects a rotational element of the first planetary gear train and a rotational element of the second planetary gear train to each other. 
     The input shaft is selectively connected to a second rotational element of the first planetary gear train and a third rotational element of the second planetary gear train via a second clutch, the input shaft is selectively connected to a third rotational element of the third planetary gear train and a second rotational element of the fourth planetary gear train via a third clutch, the input shaft is selectively connected to a first rotational element of the first planetary gear train via a fourth clutch, the output shaft is permanently connected to a second rotational element of the third planetary gear train, and a third rotational element of the first planetary gear train is permanently connected to a third rotational element of the fourth planetary gear train. 
     The first complex planetary gear train is configured so that a second rotational element of the first planetary gear train and a third rotational element of the second planetary gear train are permanently connected to each other, and a third rotational element of the first planetary gear train and a second rotational element of the second planetary gear train are selectively connected to each other via the first clutch. 
     The second complex planetary gear train is configured so that a first rotational element of the third planetary gear train and a first rotational element of the fourth planetary gear train are permanently connected to each other, and a third rotational element of the third planetary gear train and a second rotational element of the fourth planetary gear train are permanently connected to each other. 
     First, second, and third rotational elements of the first planetary gear train sequentially correspond to a first sun gear, a first carrier, and a first ring gear, first, second, and third rotational elements of the second planetary gear train sequentially correspond to a second sun gear, a second carrier, and a second ring gear, first, second, and third rotational elements of the third planetary gear train sequentially correspond to a third sun gear, a third carrier, and a third ring gear, first, second, and third rotational elements of the fourth planetary gear train sequentially correspond to a fourth sun gear, a fourth carrier, and a fourth ring gear, first complex planetary gear train is configured as a CR-CR type complex planetary gear train when the first carrier is permanently connected to the second ring gear and when the first ring gear is selectively connected to the second carrier via the first clutch. 
     The second complex planetary gear train is configured as a Simpson type complex planetary gear train when the third sun gear is permanently connected to the fourth sun gear and when the third ring gear is permanently connected to the fourth carrier, and the fourth ring gear is permanently connected to the first ring gear. 
     The input shaft is permanently connected to the second sun gear, is selectively connected to a connector between the first carrier and the second ring gear via a second clutch and a connector between the third ring gear and the fourth carrier via a third clutch, and is selectively connected to the first sun gear via a fourth clutch, and the output shaft is connected to the third carrier. 
     The first brake is installed so as to be able to selectively lock the connector between the first carrier and the second ring gear, the second brake is installed so as to be able to selectively lock the first sun gear, and the third brake is installed so as to be able to selectively lock a connector between the third sun gear and the fourth sun gear. 
     The transmission may further include a one-way clutch that prevents the connector between the first carrier and the second ring gear from rotating in a reverse direction. 
     According to the present invention, the transmission employs as few parts as possible to provide forward 11-speed and reverse 1-speed gear ratios while having a relatively simple configuration, thereby allowing the operational state of an engine connected to the transmission to be an optimal state, and thus making it possible to improve fuel efficiency and to secure smooth driving performance of the vehicle. 
     The methods and apparatuses of the present invention may have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows configuration of a transmission for a vehicle according to an exemplary embodiment of the present invention. 
         FIG. 2  shows an operational chart of operating elements of the transmission of  FIG. 1 . 
         FIG. 3  is a lever diagram explaining operation of the transmission of  FIG. 1 . 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
     In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
     DETAILED DESCRIPTION 
     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 the 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 may include d within the spirit and scope of the invention as defined by the appended claims. 
     Referring to  FIGS. 1 to 3 , a transmission for a vehicle according to an exemplary embodiment of the present invention may include a first complex planetary gear train CG 1  in which a first planetary gear train PG 1  and a second planetary gear train PG 2  are coupled to each other, a second complex planetary gear train CG 2  in which a third planetary gear train PG 3  and a fourth planetary gear train PG 4  are coupled to each other and at least one rotational element thereof is connected with a rotational element of the first complex planetary gear train CG 1 , an input shaft IN which is permanently connected to at least one rotational element of the first complex planetary gear train CG 1  and is selectively connected to another rotational element of the first complex planetary gear train CG 1  and a rotational element of the second complex planetary gear train CG 2 , an output shaft OUT which is connected to one of the rotational elements of the second complex planetary gear train CG 2 , first and second brakes B 1  and B 2  which lock the rotational elements of the first complex planetary gear train CG 1 , a third brake B 3  which locks the rotational element of the second complex planetary gear train CG 2 , and a first clutch CL 1  which selectively connects the rotational element of the first planetary gear train PG 1  and the rotational element of the second planetary gear train PG 2  to each other. 
     As described above, the input shaft IN is connected to the rotational elements of the first and second complex planetary gear trains CG 1  and CG 2  via a plurality of paths. In the present embodiment, the input shaft IN is permanently connected to a first rotational element of the second planetary gear train PG 2 . In addition to this, the input shaft IN is selectively connected to the second rotational element of the first planetary gear train PG 1  and the third rotational element of the second planetary gear train PG 2  via a second clutch CL 2 , to a third rotational element of the third planetary gear train PG 3  and a second rotational element of the fourth planetary gear train PG 4  via a third clutch CL 3 , and to a first rotational element of the first planetary gear train PG 1  via a fourth clutch CL 4 . 
     Further, the output shaft OUT is connected to a second rotational element of the third planetary gear train PG 3 . A third rotational element of the first planetary gear train PG 1  is permanently connected to a third rotational element of the fourth planetary gear train PG 4 . 
     The first complex planetary gear train CG 1  is configured so that a second rotational element of the first planetary gear train PG 1  is permanently connected to a third rotational element of the second planetary gear train PG 2 , and that a third rotational element of the first planetary gear train PG 1  is selectively connected to a second rotational element of the second planetary gear train PG 2  via the first clutch CL 1 , and vice versa. 
     The second complex planetary gear train CG 2  is configured to permanently connect a first rotational element of the third planetary gear train PG 3  and a first rotational element of the fourth planetary gear train PG 4  to each other and a third rotational element of the third planetary gear train PG 3  and a second rotational element of the fourth planetary gear train PG 4  to each other. 
     Herein, the first, second, and third rotational elements of the first planetary gear train PG 1  are sequentially referred to as a first sun gear S 1 , a first carrier C 1 , and a first ring gear R 1 . The first, second, and third rotational elements of the second planetary gear train PG 2  are sequentially referred to as a second sun gear S 2 , a second carrier C 2 , and a second ring gear R 2 . The first, second, and third rotational elements of the third planetary gear train PG 3  are sequentially referred to as a third sun gear S 3 , a third carrier C 3 , and a third ring gear R 3 . The first, second, and third rotational elements of the fourth planetary gear train PG 4  are sequentially referred to as a fourth sun gear S 4 , a fourth carrier C 4 , and a fourth ring gear R 4 . 
     Thus, in the first complex planetary gear train CG 1 , the first carrier C 1  is permanently connected to the second ring gear R 2 , and the first ring gear R 1  is selectively connected to the second carrier C 2  via the first clutch CL 1 . When the selective connection is made by the first clutch CL 1 , the first complex planetary gear train CG 1  is configured as a CR-CR type complex planetary gear train. 
     Further, in the second complex planetary gear train CG 2 , the third sun gear S 3  is permanently connected to a fourth sun gear S 4 , and the third ring gear R 3  is permanently connected to the fourth carrier C 4 . Thereby, the second complex planetary gear train CG 2  is configured as a Simpson type complex planetary gear train. 
     The input shaft IN is permanently connected to the second sun gear S 2 , is selectively connected to a connector between the first carrier C 1  and the second ring gear R 2  via the second clutch CL 2  and a connector between the third ring gear R 3  and the fourth carrier C 4  via the third clutch CL 3 , and is selectively connected to the first sun gear S 1  via the fourth clutch CL 4 . The output shaft OUT is connected to the third carrier C 3 , and the fourth ring gear R 4  is permanently connected to the first ring gear R 1 . 
     The first brake B 1  is installed so as to be able to selectively lock the connector between the first carrier C 1  and the second ring gear R 2 . The second brake B 2  is installed so as to be able to selectively lock the first sun gear  51 . The third brake B 3  is installed so as to be able to selectively lock a connector between the third sung gear S 3  and the fourth sun gear S 4 . 
     Further, to prevent the connector between the first carrier C 1  and the second ring gear R 2  from rotating in reverse, a one-way clutch F 1  is provided. 
     The first to fourth clutches CL 1  to CL 4  and the first to third brakes B 1  to B 3  are operated as in Table of  FIG. 2 . Thereby, the transmission for a vehicle configured as described above realizes forward 1-speed to 11-speed gear ratios and a reverse 1-speed gear ratio. This operation is shown in a lever diagram in  FIG. 3   
     As shown on the left side of  FIG. 3 , the first complex planetary gear train CG 1  realizes two forward reduction ratios, one reverse reduction ratio, one step-up ratio, one 11 ratio, and one zero ratio. The second complex planetary gear train CG 2  to which power shifted by this gear ratios realizes forward 11-speed and reverse 1-speed gear ratios as shown in the right side of  FIG. 3 . 
     The foregoing descriptions of specific exemplary embodiments of the present invention may 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.