Abstract:
A transmission for a vehicle employs four planetary gear trains to realizing at least forward 10-speed and reverse 3-speed gear ratios, thereby reducing the number of rotations of a second sun gear of a second planetary gear train so as to increase the efficiency of power transmission and to improve the longevity of related components of the second planetary gear train, such as a pinion gear, a pinion shaft, and a needle roller bearing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority of Korean Patent Application Number 10-2011-0095033 filed Sep. 21, 2011, the entire contents of which application is incorporated herein for all purposes by this reference. 
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates, in general, to a transmission for a vehicle, and, more particularly, to a structure of a transmission for a vehicle, capable of realizing forward 10-speed and reverse 4-speed gear ratios. 
     2. Description of Related Art 
       FIG. 1  shows a structure of a conventional forward 10-speed and reverse 3-speed transmission. The transmission is made up of a first compound planetary gear train CG 1  having a first planetary gear train PG 1  and a second planetary gear train PG 2 , and a second compound planetary gear train CG 2  having a third planetary gear train PG 3  and a fourth planetary gear train PG 4 . The first planetary gear train PG 1  is made up of a first sun gear S 1 , a first carrier C 1 , and a first ring gear R 1 . The second planetary gear train PG 2  is made up of a second sun gear S 2 , a second carrier C 2 , and a second ring gear R 2 . The third planetary gear train PG 3  is made up of a third sun gear S 3 , a third carrier C 3 , and a third ring gear R 3 . The fourth planetary gear train PG 4  is made up of a four sun gear S 4 , a four carrier C 4 , and a fourth ring gear R 4 . The first ring gear R 1  and the second carrier C 2  are permanently connected to each other, and are integrally connected to the third sun gear S 3 . 
     Further, the transmission is equipped with: a first clutch CL 1 , a second clutch CL 2 , and a third clutch CL 3 ; a first brake B 1 , a second brake B 2 , a third brake B 3 , and fourth brake B 4 ; and one one-way clutch F 1 . An input shaft IN is input by means of first to third clutches CL 1  to CL 3 , and an output shaft OUT is connected to the third ring gear R 3  and the fourth carrier C 4 . 
     The conventional 10-speed transmission as mentioned above realizes forward 10-speed and reverse 3-speed gear ratios by means of a combination of components as shown in  FIG. 2 , and a lever diagram thereof is shown in  FIG. 3 . 
     In the conventional transmission configured as mentioned above, the rotational speed of the second sun gear S 2  is frequently excessive. As a result, the efficiency of power transmission is reduced, and the durability of related components of the second planetary gear train PG 2  such as a pinion gear, a pinion shaft, and a needle roller bearing, is reduced. 
     That is, referring to  FIGS. 2 and 3 , in the 4-speed and 6-speed gear ratios in which the second clutch CL 2  and the second brake B 2  are operated at the same time, the rotational speed of the second gear S 2  is excessively high. 
     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. 
     SUMMARY OF INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and proposes a transmission for a vehicle, which employs four planetary gear trains to realize at least forward 10-speed and reverse 3-speed gear ratios, thereby reducing the number of rotations of a second sun gear of a second planetary gear train so as to increase the efficiency of power transmission and to improve the longevity of related components of the second planetary gear train, such as a pinion gear, a pinion shaft, and a needle roller bearing. 
     Various aspects of the present invention provide for a transmission for a vehicle, which includes: a first compound planetary gear train in which a first planetary gear train and a second planetary gear train are connected to each other; a second compound planetary gear train which is connected with the first compound planetary gear train and in which a third planetary gear train and a fourth planetary gear train are connected to each other; an input shaft which is connected to the first compound planetary gear train; an output shaft which is connected to the second compound planetary gear train; a first clutch which selectively connects a third rotational element of the first planetary gear train and a second rotational element of the second planetary gear train to each other; a second clutch which selectively connects the input shaft to a second rotational element of the first planetary gear train and a third rotational element of the second planetary gear train; a third clutch which selectively connects the input shaft to a third rotational element of the third planetary gear train; a first brake B 1  which selectively locks the second rotational element of the first planetary gear train and the third rotational element of the second planetary gear train; a second brake which selectively locks a first rotational element of the first planetary gear train; a third brake which selectively locks a first rotational element of the third planetary gear train along with a first rotational element of the fourth planetary gear train; and a fourth brake which selectively locks the third rotational element of the third planetary gear train along with a second rotational element of the fourth planetary gear train. 
     According to the present invention, the transmission employs four planetary gear trains to realize at least forward 10-speed and reverse 3-speed gear ratios, thereby reducing the number of rotations of a second sun gear of a second planetary gear train so as to increase the efficiency of power transmission and to improve the longevity of related components of the second planetary gear train, such as the pinion gear, pinion shaft, and needle roller bearing. 
     The methods and apparatuses of the present invention 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 conventional transmission for a vehicle. 
         FIG. 2  shows an operation chart of operating elements of the transmission of  FIG. 1 . 
         FIG. 3  is a lever diagram explaining operation of the transmission of  FIG. 1 . 
         FIG. 4  shows configuration of an exemplary transmission for a vehicle according to the present invention; 
         FIG. 5  shows an operation chart of operating elements of the transmission of  FIG. 4 . 
         FIG. 6  is a lever diagram explaining operation of the transmission of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts. 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. 
     Referring to  FIGS. 4 to 6 , a transmission for a vehicle according to various embodiments of the present invention includes: a first compound planetary gear train CG 1  in which a first planetary gear train PG 1  and a second planetary gear train PG 2  are connected to each other; a second compound planetary gear train CG 2  which is connected with the first compound planetary gear train CG 1  and in which a third planetary gear train PG 3  and a fourth planetary gear train PG 4  are connected to each other; an input shaft IN which is connected to the first compound planetary gear train CG 1 ; an output shaft OUT which is connected to the second compound planetary gear train CG 2 ; a first clutch CL 1  which selectively connects a third rotational element of the first planetary gear train PG 1  and a second rotational element of the second planetary gear train PG 2  to each other; a second clutch CL 2  which selectively connects the input shaft IN to a second rotational element of the first planetary gear train. PG 1  and a third rotational element of the second planetary gear train PG 2 ; a third clutch CL 3  which selectively connects the input shaft IN to a third rotational element of the third planetary gear train PG 3 ; a first brake B 1  which selectively locks 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 ; a second brake B 2  which selectively locks a first rotational element of the first planetary gear train PG 1 ; a third brake B 3  which selectively locks a first rotational element of the third planetary gear train PG 3  along with a first rotational element of the fourth planetary gear train PG 4 ; and a fourth brake B 4  which selectively locks the third rotational element of the third planetary gear train PG 3  along with a second rotational element of the fourth planetary gear train PG 4 . 
     The input shaft IN is permanently connected to a first rotational element of the second planetary gear train PG 2 . 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 . Further, the output shaft OUT is connected to a second rotational element of the third planetary gear train PG 3 . 
     The first compound planetary gear train CG 1  is configured to permanently connect 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  and to selectively connect the third rotational element of the first planetary gear train PG 1  and the second rotational element of the second planetary gear train PG 2  using the first clutch CL 1 . 
     The second compound planetary gear train CG 2  is configured to permanently connect the first rotational element of the third planetary gear train PG 3  and the first rotational element of the fourth planetary gear train PG 4  and to permanently connect the third rotational element of the third planetary gear train PG 3  and the second rotational element of the fourth planetary gear train PG 4 . 
     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 compound 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 compound planetary gear train CG 1  is configured as a CR-CR type compound planetary gear train. 
     Further, in the second compound 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 compound planetary gear train CG 2  is configured as a Simpson type compound planetary gear train, in which the fourth ring gear R 4  is permanently connected to the first ring gear R 1 . 
     Further, the input shaft IN is selectively connected to a connector between the first carrier C 1  and the first ring gear R 1  via the second clutch CL 2 , is permanently connected to the second sun gear S 2 , and is selectively connected to a connector between the third ring gear R 3  and the fourth carrier C 4  via the third clutch CL 3 . The output shaft OUT is connected to the third carrier C 3 . 
     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 S 1 . 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 . The fourth brake B 4  is installed so as to be able to selectively lock a connector between the third ring gear R 3  and the fourth carrier C 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. 
     With the aforementioned configuration, the transmission for a vehicle according to various embodiments of the present invention has gear ratios on the basis of the operational chart of  FIG. 5 , and this operation can be arranged as in the lever diagram of  FIG. 6 . 
     In particular, the inventive transmission is designed to permanently connect the second sun gear S 2  of the second planetary gear train PG 2  to the input shaft IN, and to variably connect the first ring gear R 1  of the first planetary gear train PG 1  and the second carrier C 2  of the second planetary gear train PG 2  using the first clutch CL 1 , thereby reducing the number of rotations of the second sun gear S 2  so as to increase the efficiency of power transmission and to improve the durability of a pinion gear, a pinion shaft, and a needle roller bearing of the second planetary gear train PG 2 . 
     That is, the second sun gear S 2  is connected to the input shaft IN, so that the second sun gear S 2  does not rotate above a rotation speed of the input shaft IN, and the first clutch CL 1  is released in 4-speed, 6-speed, and reverse 4-speed gear ratios where the second clutch CL 2  is operated along with the second brake B 2 , so that the rotational speed of the second sun gear S 2  maintains that of the input shaft IN without exceeding that of the input shaft IN. 
     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.