Abstract:
The present disclosure provides a planetary gear train of an automatic transmission for a vehicle. The planetary gear train may include: an input shaft receiving torque of an engine; an output shaft outputting changed torque; a first planetary gear set including first, second, and third rotation elements; a second planetary gear set including fourth, fifth, and sixth rotation elements; a third planetary gear set including seventh, eighth, and ninth rotation elements; a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements. The planetary gear train improves power delivery performance and fuel economy by achieving at least eleven forward speed stages and widening speed ratio (or gear ratio) with a reduced number of constituent elements being used, and secures linearity of step ratios.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2016-0023312, filed on Feb. 26, 2016, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The present disclosure relates to an automatic transmission for a vehicle. More particularly, the present disclosure relates to a planetary gear train of an automatic transmission for a vehicle. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    Generally, an automatic transmission achieving more speed stages has been developed to enhance fuel economy and optimize drivability. 
         [0005]    Such an automatic transmission achieving more speed stages is preferred to maximize power performance and driving efficiency according to downsizing of an engine. Particularly, we have discovered that a high efficiency multiple-speeds transmission having excellent linearity of step ratios can be used as an index closely related to drivability such as acceleration before and after shift and rhythmical engine speed in order to secure competitiveness in the automatic transmission field. 
         [0006]    However, in the automatic transmission, as the number of speed stages increase, the number of internal components increase, and as a result, mountability, cost, weight, transmission efficiency, and the like may still deteriorate. 
         [0007]    Accordingly, development of a planetary gear train which may achieve improved efficiency with a small number of components can increase a fuel efficiency enhancement effect through the multiple-speeds. 
         [0008]    In this aspect, in recent years, 8-speed automatic transmissions tend to be implemented and the research and development of a planetary gear train capable of implementing more speed stages has also been actively conducted. 
         [0009]    However, since a conventional 8-speed automatic transmission has gear ratio span of 6.5-7.5 (gear ratio span is an important factor for securing linearity of step ratios), improvement of power performance and fuel economy may not be very good. 
         [0010]    In addition, if an 8-speed automatic transmission has a gear ratio span larger than 9.0, it is hard to secure linearity of step ratios. Therefore, driving efficiency of an engine and drivability of a vehicle may be deteriorated. 
         [0011]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. 
         [0012]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
       SUMMARY 
       [0013]    The present disclosure provides a planetary gear train of an automatic transmission for a vehicle having advantages of improving power delivery performance and fuel economy by achieving at least eleven forward speed stages and one reverse speed stage, and widening a gear ratio span and of securing linearity of step ratios. 
         [0014]    A planetary gear train of an automatic transmission for a vehicle according to one form of the present disclosure may include: an input shaft receiving torque of an engine; an output shaft outputting torque; a first planetary gear set including first, second, and third rotation elements; a second planetary gear set including fourth, fifth, and sixth rotation elements; a third planetary gear set including seventh, eighth, and ninth rotation elements; a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements; a first shaft connected with the first rotation element; a second shaft connecting the second rotation element, the sixth rotation element, and the seventh rotation element; a third shaft connecting the third rotation element and the fifth rotation element; a fourth shaft connected with the fourth rotation element; a fifth shaft connected with the eighth rotation element and directly connected with the output shaft; a sixth shaft connected with the ninth rotation element; a seventh shaft connected with the eleventh rotation element, selectively connected with the third shaft or the fourth shaft, and directly connected with the input shaft; and an eighth shaft connected with one of the tenth rotation element or the twelfth rotation element. 
         [0015]    The first shaft, the third shaft, the fourth shaft, and the sixth shaft may be selectively connected with the transmission housing. 
         [0016]    The eighth shaft may be connected with the twelfth rotation element and selectively connected with the fifth shaft, and the tenth rotation element may be connected with the second shaft. 
         [0017]    The planetary gear train may further include: a first clutch selectively connecting the fifth shaft and the eighth shaft; a second clutch selectively connecting the fourth shaft and the seventh shaft; a third clutch selectively connecting the third shaft and the seventh shaft; a first brake selectively connecting the fourth shaft with the transmission housing; a second brake selectively connecting the first shaft with the transmission housing; a third brake selectively connecting the third shaft with the transmission housing; and a fourth brake selectively connecting the sixth shaft with the transmission housing. 
         [0018]    The eighth shaft may be connected with the tenth rotation element and selectively connected with the second shaft, and the twelfth rotation element may be connected with the fifth shaft. 
         [0019]    The planetary gear train may further include: a first clutch selectively connecting the second shaft and the eighth shaft; a second clutch selectively connecting the fourth shaft and the seventh shaft; a third clutch selectively connecting the third shaft and the seventh shaft; a first brake selectively connecting the fourth shaft with the transmission housing; a second brake selectively connecting the first shaft with the transmission housing; a third brake selectively connecting the third shaft with the transmission housing; and a fourth brake selectively connecting the sixth shaft with the transmission housing. 
         [0020]    The first, second, and third rotational elements of the first planetary gear set may be respectively a first sun gear, a first planet carrier, and a first ring gear of the first planetary gear set, the fourth, fifth, and sixth rotational elements of the second planetary gear set may be respectively a second sun gear, a second planet carrier, and a second ring gear of the second planetary gear set, the seventh, eighth, and ninth rotational elements of the third planetary gear set may be respectively a third sun gear, a third planet carrier, and a third ring gear of the third planetary gear set, and the tenth, eleventh, and twelfth rotational elements of the fourth planetary gear set may be respectively a fourth sun gear, a fourth planet carrier, and a fourth ring gear of the fourth planetary gear set. 
         [0021]    One form of the present disclosure may achieve at least eleven forward speed stages and one reverse speed stage by combining four planetary gear sets being simple planetary gear sets with seven control elements. 
         [0022]    In addition, driving efficiency of the engine may be maximized by at least eleven forward speed stages. In addition, since linearity of step ratios can be secured due to multiple speed stages, drivability such as acceleration before and after shift, rhythmical engine speed, and so on may be improved. 
         [0023]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0024]    In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
           [0025]      FIG. 1  is a schematic diagram of a planetary gear train according to a first form of the present disclosure; 
           [0026]      FIG. 2  is an operational chart for respective friction elements at respective shift-stages in a planetary gear train according to a form of the present disclosure; and 
           [0027]      FIG. 3  is a schematic diagram of a planetary gear train according to a second form of the present disclosure. 
       
    
    
       [0028]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
       DESCRIPTION OF SYMBOLS 
       [0000]    
       
         
           
             B 1 , B 2 , B 3 , B 4 : first, second, third, and fourth brakes 
             C 1 , C 2 , C 3 : first, second, and third clutches 
             PG 1 , PG 2 , PG 3 , PG 4 : first, second, third, and fourth planetary gear sets 
             S 1 , S 2 , S 3 , S 4 : first, second, third, and fourth sun gears 
             PC 1 , PC 2 , PC 3 , PC 4 : first, second, third, and fourth planet carriers 
             R 1 , R 2 , R 3 , R 4 : first, second, third, and fourth ring gears 
             IS: input shaft 
             OS: output shaft 
             TM 1 , TM 2 , TM 3 , TM 4 , TM 5 , TM 6 , TM 7 , TM 8 : first, second, third, fourth, fifth, sixth, seventh, and eighth shafts 
           
         
       
     
       DETAILED DESCRIPTION 
       [0038]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0039]    Hereinafter, one form of the present disclosure will be described in detail with reference to drawings. 
         [0040]    However, parts which are not related with the description are omitted for clearly describing the forms of the present disclosure and like reference numerals refer to like or similar elements throughout the specification. 
         [0041]    In the following description, dividing names of components into first, second, and the like is to divide the names because the names of the components are the same as each other and an order thereof is not particularly limited. As used herein, “connect” and its variants includes connection for transmission of force such as torque, e.g., a first component connected to a second component for rotation therewith, or a first component connected to a second component for fixation of the components, e.g. braking or restraining movement. 
         [0042]      FIG. 1  is a schematic diagram of a planetary gear train according to a first form of the present disclosure. 
         [0043]    Referring to  FIG. 1 , a planetary gear train includes first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  arranged on the same axis, an input shaft IS, an output shaft OS, eight shafts TM 1  to TM 8  interconnecting rotational elements of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , three clutches C 1  to C 3  and four brakes B 1  to B 4  as control elements, and a transmission housing H. 
         [0044]    Torque input from the input shaft IS is shifted by cooperative operation of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , and then output through the output shaft OS. 
         [0045]    The planetary gear sets are arranged in the order of first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , from an engine side. 
         [0046]    The input shaft IS is an input member and the torque from a crankshaft of an engine is input into the input shaft IS, after being torque-converted through a torque converter. 
         [0047]    The output shaft OS is an output member, is disposed in parallel with the input shaft IS, and transmits driving torque to a driving wheel through a differential apparatus. 
         [0048]    The first planetary gear set PG 1  is a single pinion planetary gear set and includes a first sun gear S 1 , a first planet carrier PC 1  rotatably supporting a first pinion P 1  that is externally meshed with the first sun gear S 1 , and a first ring gear R 1  that is internally meshed with the first pinion P 1  respectively as first, second, and third rotation elements N 1 , N 2 , and N 3 . 
         [0049]    The second planetary gear set PG 2  is a single pinion planetary gear set and includes a second sun gear S 2 , a second planet carrier PC 2  rotatably supporting a second pinion P 2  that is externally meshed with the second sun gear S 2 , and a second ring gear R 2  that is internally meshed with the second pinion P 2  respectively as fourth, fifth, and sixth rotation elements N 4 , N 5 , and N 6 . 
         [0050]    The third planetary gear set PG 3  is a single pinion planetary gear set and includes a third sun gear S 3 , a third planet carrier PC 3  rotatably supporting a third pinion P 3  that is externally meshed with the third sun gear S 3 , and a third ring gear R 3  that is internally meshed with the third pinion P 3  respectively as seventh, eighth, and ninth rotation elements N 7 , N 8 , and N 9 . 
         [0051]    The fourth planetary gear set PG 4  is a single pinion planetary gear set and includes a fourth sun gear S 4 , a fourth planet carrier PC 4  rotatably supporting a fourth pinion P 4  that is externally meshed with the fourth sun gear S 4 , and a fourth ring gear R 4  that is internally meshed with the fourth pinion P 4  respectively as tenth, eleventh, and twelfth rotation elements N 10 , N 11 , and N 12 . 
         [0052]    The second rotation element N 2 , the sixth rotation element N 6 , the seventh rotation element N 7  and the tenth rotation element N 10  are directly connected with each other, and the third rotation element N 3  is directly connected to the fifth rotation element N 5  by two shafts among the eight shafts TM 1  to TM 8 . 
         [0053]    The eight shafts TM 1  to TM 8  will be described in further detail. 
         [0054]    The eight shafts TM 1  to TM 8  directly connect a plurality of rotation elements among the rotation elements of the planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , and are rotation members that are directly connected to any one rotation element of the planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  and rotate with the any one rotation element to transmit torque, or are fixed members that directly connect any one rotation element (or more) of the planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  to the transmission housing H to fix the any one rotation element. 
         [0055]    The first shaft TM 1  is connected with the first rotation element N 1  (first sun gear S 1 ) and selectively connected with the transmission housing H. 
         [0056]    The second shaft TM 2  directly connects the second rotation element N 2  (first planet carrier PC 1 ), the sixth rotation element N 6  (second ring gear R 2 ), the seventh rotation element N 7  (third sun gear S 3 ) and the tenth rotation element N 10  (fourth sun gear S 4 ). 
         [0057]    The third shaft TM 3  directly connects the third rotation element N 3  (first ring gear R 1 ) and the fifth rotation element N 5  (second planet carrier PC 2 ), and is selectively connected with the transmission housing H. 
         [0058]    The fourth shaft TM 4  is connected with the fourth rotation element N 4  (second sun gear S 2 ), and selectively connected with the transmission housing H. 
         [0059]    The fifth shaft TM 5  is connected with the eighth rotation element N 8  (third planet carrier PC 3 ), and directly connected with the output shaft OS, thereby always acting as an output element. 
         [0060]    The sixth shaft TM 6  is connected with the ninth rotation element N 9  (third ring gear R 3 ), and selectively connected with the transmission housing H. 
         [0061]    The seventh shaft TM 7  is connected with the eleventh rotation element N 11  (fourth planet carrier PC 4 ), selectively connected with the third shaft TM 3  and the fourth shaft TM 4 , and directly connected with the input shaft IS, thereby always acting as an input element. 
         [0062]    The eighth shaft TM 8  is connected with the twelfth rotation element N 12  (fourth ring gear R 4 ), and selectively connected with the fifth shaft TM 5 . 
         [0063]    In addition, three clutches C 1 , C 2 , and C 3  are disposed at portions at which any two shafts among the eight shafts TM 1  to TM 8  including the input shaft IS and the output shaft OS are selectively connected to each other. 
         [0064]    In addition, four brakes B 1 , B 2 , B 3 , and B 4  are disposed at portions at which any one shaft among the eight shafts TM 1  to TM 8  is selectively connected to the transmission housing H. 
         [0065]    Arrangements of the three clutches C 1  to C 3  and the four brakes B 1  to B 4  are described in detail. 
         [0066]    The first clutch C 1  is disposed between the fifth shaft TM 5  and the eighth shaft TM 8 , and selectively connects the fifth shaft TM 5  with the eighth shaft TM 8 . 
         [0067]    The second clutch C 2  is disposed between the fourth shaft TM 4  and the seventh shaft TM 7 , and selectively connects the fourth shaft TM 4  and the seventh shaft TM 7 . 
         [0068]    The third clutch C 3  is disposed between the third shaft TM 3  and the seventh shaft TM 7 , and selectively connects the third shaft TM 3  and the seventh shaft TM 7 . 
         [0069]    The first brake B 1  is disposed between the fourth shaft TM 4  and the transmission housing H, and selectively connects the fourth shaft TM 4  with the transmission housing H. 
         [0070]    The second brake B 2  is disposed between the first shaft TM 1  and the transmission housing H, and selectively connects the first shaft TM 1  with the transmission housing H. 
         [0071]    The third brake B 3  is disposed between the third shaft TM 3  and the transmission housing H, and selectively connects the third shaft TM 3  with the transmission housing H. 
         [0072]    The fourth brake B 4  is disposed between the sixth shaft TM 6  and the transmission housing H, and selectively connects the sixth shaft TM 6  with the transmission housing H. 
         [0073]    The control elements including the first, second, and third clutches C 1 , C 2 , and C 3  and the first, second, third, and fourth brakes B 1 , B 2 , B 3 , and B 4  may be multi-plates friction elements of wet type that are operated by hydraulic pressure, although other types of clutches or brakes may also be employed. 
         [0074]      FIG. 2  is an operational chart for respective friction elements at respective shift-stages in a planetary gear train according to a first form of the present disclosure. 
         [0075]    Referring to  FIG. 2 , three control elements among the first, second, and third clutches C 1 , C 2 , and C 3  and the first, second, third, and fourth brakes B 1 , B 2 , B 3 , and B 4  are operated at each speed stage in the planetary gear train. The forms of the present disclosure can achieve at least one reverse speed stage and at least eleven forward speed stages. 
         [0076]    The second clutch C 2  and second and fourth brakes B 2  and B 4  are simultaneously operated at a first forward speed stage D 1 . 
         [0077]    In a state that the fourth shaft TM 4  is connected to the seventh shaft TM 7 , torque of the input shaft IS is input to the fourth shaft TM 4  and the seventh shaft TM 7 . In addition, the first shaft TM 1  and the sixth shaft TM 6  are operated as the fixed elements. Therefore, the torque of the input shaft IS is shifted into the first forward speed stage, and the first forward speed stage is output to the output shaft OS connected to the fifth shaft TM 5 . 
         [0078]    The third clutch C 3  and second and fourth brakes B 2  and B 4  are simultaneously operated at a second forward speed stage D 2 . 
         [0079]    In a state that the third shaft TM 3  is connected to the seventh shaft TM 7 , the torque of the input shaft IS is input to the third shaft TM 3  and the seventh shaft TM 7 . In addition, the first shaft TM 1  and the sixth shaft TM 6  are operated as the fixed elements. Therefore, the torque of the input shaft IS is shifted into the second forward speed stage, and the second forward speed stage is output to the output shaft OS connected to the fifth shaft TM 5 . 
         [0080]    The second and third clutches C 2  and C 3  and fourth brake B 4  are simultaneously operated at a third forward speed stage D 3 . 
         [0081]    In a state that the fourth shaft TM 4  is connected to the seventh shaft TM 7  and the third shaft TM 3  is connected to the seventh shaft TM 7 , the torque of the input shaft IS is input to the third shaft TM 3 , the fourth shaft TM 4  and the seventh shaft TM 7 . In addition, the sixth shaft TM 6  is operated as the fixed elements. Therefore, the torque of the input shaft IS is shifted into the third forward speed stage, and the third forward speed stage is output to the output shaft OS connected to the fifth shaft TM 5 . 
         [0082]    The third clutch C 3  and first and fourth brakes B 1  and B 4  are simultaneously operated at a fourth forward speed stage D 4 . 
         [0083]    In a state that the third shaft TM 3  is connected to the seventh shaft TM 7 , the torque of the input shaft IS is input to the seventh shaft TM 7 . In addition, the fourth shaft TM 4  and the sixth shaft TM 6  are operated as the fixed elements. Therefore, the torque of the input shaft IS is shifted into the fourth forward speed stage, and the fourth forward speed stage is output to the output shaft OS connected to the fifth shaft TM 5 . 
         [0084]    The first clutch C 1  and first and fourth brakes B 1  and B 4  are simultaneously operated at a fifth forward speed stage D 5 . 
         [0085]    In a state that the fifth shaft TM 5  is connected to the eighth shaft TM 8 , the torque of the input shaft IS is input to the seventh shaft TM 7 . In addition, the fourth shaft TM 4  and the sixth shaft TM 6  are operated as the fixed elements. Therefore, the torque of the input shaft IS is shifted into the fifth forward speed stage, and the fifth forward speed stage is output to the output shaft OS connected to the fifth shaft TM 5 . 
         [0086]    The first and third clutches C 1  and C 3  and first brake B 1  are simultaneously operated at a sixth forward speed stage D 6 . 
         [0087]    In a state that the fifth shaft TM 5  is connected to the eighth shaft TM 8  and the third shaft TM 3  is connected to the seventh shaft TM 7 , the torque of the input shaft IS is input to the third shaft TM 3  and the seventh shaft TM 7 . In addition, the fourth shaft TM 4  is operated as the fixed elements. Therefore, the torque of the input shaft IS is shifted into the sixth forward speed stage, and the sixth forward speed stage is output to the output shaft OS connected to the fifth shaft TM 5 . 
         [0088]    The first, second, and third clutches C 1 , C 2 , and C 3  are simultaneously operated at a seventh forward speed stage D 7 . 
         [0089]    Since the fifth shaft TM 5  is connected to the eighth shaft TM 8 , the fourth shaft TM 4  is connected to the seventh shaft TM 7 , and the third shaft TM 3  is connected to the seventh shaft TM 7 , all the planetary gear sets become lock-up states. In this state, the torque of the input shaft IS is input to the third shaft TM 3 , the fourth shaft TM 4 , and seventh shaft TM 7  and the seventh forward speed stage is output to the output shaft OS connected to the seventh shaft TM 7 . Rotation speed that is the same as rotation speed of the input shaft IS is output at the seventh forward speed stage. 
         [0090]    The first and third clutches C 1  and C 3  and the second brake B 2  are simultaneously operated at an eighth forward speed stage D 8 . 
         [0091]    In a state that the fifth shaft TM 5  is connected to the eighth shaft TM 8  and the third shaft TM 3  is connected to the seventh shaft TM 7 , the torque of the input shaft IS is input to the third shaft TM 3  and the seventh shaft TM 7 . In addition, the first shaft TM 1  is operated as the fixed elements. Therefore, the torque of the input shaft IS is shifted into the eighth forward speed stage, and the eighth forward speed stage is output to the output shaft OS connected to the fifth shaft TM 5 . 
         [0092]    The first and second clutches C 1  and C 2  and the second brake B 2  are simultaneously operated at a ninth forward speed stage D 9 . 
         [0093]    In a state that the fifth shaft TM 5  is connected to the eighth shaft TM 8  and the fourth shaft TM 4  is connected to the seventh shaft TM 7 , the torque of the input shaft IS is input to the fourth shaft TM 4  and the seventh shaft TM 7 . In addition, the first shaft TM 1  is operated as the fixed elements. Therefore, the torque of the input shaft IS is shifted into the ninth forward speed stage, and the ninth forward speed stage is output to the output shaft OS connected to the fifth shaft TM 5 . 
         [0094]    The first clutch C 1  and the second and third brakes B 2  and B 3  are simultaneously operated at a tenth forward speed stage D 10 . 
         [0095]    In a state that the fifth shaft TM 5  is connected to the eighth shaft TM 8 , the torque of the input shaft IS is input to the seventh shaft TM 7 . In addition, the first shaft TM 1  and the third shaft TM 3  are operated as the fixed elements. Therefore, the torque of the input shaft IS is shifted into the tenth forward speed stage, and the tenth forward speed stage is output to the output shaft OS connected to the fifth shaft TM 5 . 
         [0096]    The first and second clutches C 1  and C 2  and the third brake B 3  are simultaneously operated at an eleventh forward speed stage D 11 . 
         [0097]    In a state that the fifth shaft TM 5  is connected to the eighth shaft TM 8  and the fourth shaft TM 4  is connected to the seventh shaft TM 7 , the torque of the input shaft IS is input to the fourth shaft TM 4  and the seventh shaft TM 7 . In addition, the third shaft TM 3  is operated as the fixed elements. Therefore, the torque of the input shaft IS is shifted into the eleventh forward speed stage, and the eleventh forward speed stage is output to the output shaft OS connected to the fifth shaft TM 5 . 
         [0098]    The second clutch C 2  and the third and fourth brakes B 3  and B 4  are simultaneously operated at a reverse speed stage REV. 
         [0099]    In a state that the fourth shaft TM 4  is connected to the seventh shaft TM 7 , the torque of the input shaft IS is input to the fourth shaft TM 4  and the seventh shaft TM 7 . In addition, the third shaft TM 3  and the sixth shaft TM 6  are operated as the fixed elements. Therefore, the torque of the input shaft IS is shifted into the reverse speed stage, and the reverse speed stage is output to the output shaft OS connected to the fifth shaft TM 5 . 
         [0100]      FIG. 3  is a schematic diagram of a planetary gear train according to a second form of the present disclosure. 
         [0101]    In a planetary gear train according to a first form of the present disclosure, the eighth shaft TM 8  is connected with the twelfth rotation element N 12  (fourth ring gear R 4 ) and is selectively connected with the fifth shaft TM 5  by the first clutch C 1 , and the tenth rotation element N 10  (fourth sun gear S 4 ) is connected with the second shaft TM 2 , as shown in  FIG. 1 . 
         [0102]    However, referring to  FIG. 3 , the eighth shaft TM 8  is connected with the tenth rotation element N 10  (fourth sun gear S 4 ) and is selectively connected with the second shaft TM 2  by the first clutch C 1 , and the twelfth rotation element N 12  (fourth ring gear R 4 ) is connected with the fifth shaft TM 5 , in a planetary gear train according to a second form. 
         [0103]    As a result, the second form merely differs from a planetary gear train according to a first form in a connection relationship of rotation elements of the third and fourth planetary gear sets PG 3  and PG 4  according to the location of the first clutch C 1  but maintains a same operation and function, which is therefore not described in further detail. 
         [0104]    The planetary gear train according to the forms of the present disclosure may achieve at least eleven forward speed stages and one reverse speed stage by combining four planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  with the three clutches C 1 , C 2 , and C 3  and the fourth brakes B 1 , B 2 , B 3 , and B 4 , thereby improving an engine driving efficiency and a fuel efficiency due to multiple speed stages. 
         [0105]    In addition, since linearity of step ratios can be secured due to multiple speed stages, drivability such as acceleration before and after shift, rhythmical engine speed, and so on may be improved. 
         [0106]    While this disclosure has been described in connection with what is presently considered to be practical forms, it is to be understood that the disclosure is not limited to the disclosed forms, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the present disclosure. 
         [0107]    The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.