Abstract:
A planetary gear train of an automatic transmission for a vehicle having an input shaft for receiving torque of an engine; an output shaft for 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; and a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements, improves power delivery performance and fuel economy by achieving at least ten forward speed stages.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2016-0053330 filed on Apr. 29, 2016, the entirety of which is hereby incorporated by reference. 
     FIELD 
     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 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Generally, an automatic transmission achieving more speed stages has been developed to enhance fuel economy and improve drivability. 
     Such an automatic transmission achieving more speed stages allows for improved power performance and driving efficiency when downsizing an engine. Providing high efficiency multiple-speed transmissions with smooth step ratios that can be used as an index closely related to drivability such as acceleration before and after a shift increases competitiveness of an automatic transmission in the automotive field. 
     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. 
     Accordingly, development of a planetary gear train that improves efficiency with a small number of components may be provided in order to increase a fuel efficiency enhancement effect through the multiple-speeds. 
     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. 
     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 be minimal. 
     In addition, if an 8-speed automatic transmission has a gear ratio span larger than 9.0, we have found that it is difficult to secure linearity of step ratios. Therefore, driving efficiency of an engine and drivability of a vehicle may be deteriorated, and thus, development of high efficiency automatic transmissions which achieve at least nine forward speed stages is desired. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY 
     The present disclosure provides a planetary gear train of an automatic transmission for a vehicle capable of improving power delivery performance and fuel economy by achieving at least ten forward speed stages and one reverse speed stage, widening a gear ratio span, and securing linearity of step ratios. 
     A planetary gear train of an automatic transmission for a vehicle according to an embodiment 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 connecting the first rotational element, the sixth rotational element, the eighth rotational element and the tenth rotational element; a second shaft connected to the second rotational element and directly connected to the input shaft; a third shaft connecting the third rotational element with the seventh rotational element; a fourth shaft connected to the fourth rotational element and selectively connected to the second shaft; a fifth shaft connected to the fifth rotational element and selectively connected to the second shaft; a sixth shaft connected to the ninth rotational element; and a seventh shaft connected to the eleventh rotational element and directly connected to the output shaft. 
     The third shaft is selectively connected to the seventh shaft, the fourth shaft is selectively connected to a transmission housing in a state of not being connected to the second shaft, and the fifth shaft is selectively connected to the sixth shaft, and is selectively connected to the transmission housing in a state of not being connected to the second shaft. 
     The planetary gear train may further include an eighth shaft connected to the twelfth rotational element and selectively connected to the transmission housing. 
     The first, second, and third rotation elements of the first planetary gear set may be a first sun gear, a first planet carrier, and a first ring gear, the fourth, fifth, and sixth rotation elements of the second planetary gear set may be a second sun gear, a second planet carrier, and a second ring gear, the seventh, eighth, and ninth rotation elements of the third planetary gear set may be a third sun gear, a third planet carrier, and a third ring gear, and a tenth, eleventh, and twelfth rotation elements of the fourth planetary gear set may be a fourth sun gear, a fourth planet carrier, and a fourth ring gear, respectively. 
     In one aspect, the first, second, third, and fourth planetary gear sets may be disposed in a sequence of the second planetary gear set, the third planetary gear set, the first planetary gear set, and the fourth planetary gear set from the engine. 
     In another aspect, the first, second, third, and fourth planetary gear sets may be disposed in a sequence of the second planetary gear set, the third planetary gear set, the fourth planetary gear set, and the first planetary gear set from the engine. 
     The planetary gear train may further include: a first clutch selectively connecting the third shaft with the seventh shaft; a second clutch selectively connecting the second shaft with the fourth shaft; a third clutch selectively connecting the second shaft with the fifth shaft; a fourth clutch selectively connecting the fifth shaft with the sixth shaft; a first brake selectively connecting the fourth shaft with the transmission housing; a second brake selectively connecting the fifth shaft with the transmission housing; and a third brake selectively connecting the eighth shaft with the transmission housing. 
     A planetary gear train of an automatic transmission for a vehicle according to another exemplary embodiment 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; and a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements, wherein the input shaft is directly connected to the second rotational element, the output shaft is directly connected to the eleventh rotational element, the first rotational element is directly connected to the sixth rotational element, the eighth rotational element and the tenth rotational element, the third rotational element is directly connected to the seventh rotational element, the fourth rotational element is selectively connected to a transmission housing, the fifth rotational element is selectively connected to the ninth rotational element and is selectively connected to the transmission housing, and the eighth rotational element is selectively connected to the transmission housing. 
     The third rotational element is selectively connected to the eleventh rotational element, the fourth rotational element is selectively connected to the second rotational element in a state of not being connected to the transmission housing, and the fifth rotational element is selectively connected to the second rotational element in a state of not being connected to the transmission housing. 
     The first, second, and third rotation elements of the first planetary gear set may be a first sun gear, a first planet carrier, and a first ring gear, the fourth, fifth, and sixth rotation elements of the second planetary gear set may be a second sun gear, a second planet carrier, and a second ring gear, the seventh, eighth, and ninth rotation elements of the third planetary gear set may be a third sun gear, a third planet carrier, and a third ring gear, and the tenth, eleventh, and twelfth rotation elements of the fourth planetary gear set may be a fourth sun gear, a fourth planet carrier, and a fourth ring gear, respectively. 
     In one aspect, the first, second, third, and fourth planetary gear sets may be disposed in a sequence of the second planetary gear set, the third planetary gear set, the first planetary gear set, and the fourth planetary gear set from the engine. 
     In another aspect, the first, second, third, and fourth planetary gear sets may be disposed in a sequence of the second planetary gear set, the third planetary gear set, the fourth planetary gear set, and the first planetary gear set from the engine. 
     The planetary gear train may further include: a first clutch selectively connecting the third rotational element with the eleventh rotational element; a second clutch selectively connecting the second rotational element with the fourth rotational element; a third clutch selectively connecting the second rotational element with the fifth rotational element; a fourth clutch selectively connecting the fifth rotational element with the ninth rotational element; a first brake selectively connecting the fourth rotational element with the transmission housing; a second brake selectively connecting the fifth rotational element with the transmission housing; and a third brake selectively connecting the twelfth rotational element with the transmission housing. 
     An exemplary embodiment of the present disclosure may achieve at least ten forward speed stages and one reverse speed stage by combining four planetary gear sets being simple planetary gear sets with seven control elements. 
     In addition, since gear ratio span greater than 10.0 is secured, driving efficiency of the engine may be maximized. 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. 
     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 
       In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, references being made to the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a planetary gear train according to the first embodiment of the present disclosure; 
         FIG. 2  is an operation chart of control elements at each speed stage in the planetary gear train according to the first embodiment of the present disclosure; and 
         FIG. 3  is a schematic diagram of a planetary gear train according to the second embodiment of the present disclosure. 
     
    
    
     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 
     B 1 , B 2 , B 3 : first, second, and third brakes 
     C 1 , C 2 , C 3 , C 4 : first, second, third, and fourth 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 
     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. 
     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. 
       FIG. 1  is a schematic diagram of a planetary gear train according to the first embodiment of the present disclosure. 
     As shown in  FIG. 1 , a planetary gear train according to first embodiment of the present disclosure includes first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  disposed on the same axis, an input shaft IS, an output shaft OS, eight shafts TM 1 , TM 2 , TM 3 , TM 4 , TM 5 , TM 6 , TM 7 , and TM 8  connected to at least one of rotation elements of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , four clutches C 1 , C 2 , C 3 , and C 4  and three brakes B 1 , B 2 , and B 3  that are control elements, and a transmission housing H. 
     Torque input from the input shaft IS is changed by cooperation of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , and the changed torque is output through the output shaft OS. 
     The planetary gear set in the first embodiment of the present disclosure are disposed in a sequence of the second, third, first, and fourth planetary gear sets PG 2 , PG 3 , PG 1 , and PG 4  from the engine. 
     The input shaft IS is an input member and torque from a crankshaft of the engine is torque-converted through a torque converter to be input into the input shaft IS. 
     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. 
     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 . 
     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 . 
     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 . 
     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 . 
     The first rotational element N 1  is directly connected to the sixth rotational element N 6 , the eighth rotational element N 8 , and the tenth rotational element N 10 , and the third rotational element N 3  is directly connected to the seventh rotational element N 7  such that the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  include eight shafts TM 1 , TM 2 , TM 3 , TM 4 , TM 5 , TM 6 , TM 7 , and TM 8 . 
     The eight shafts TM 1 , TM 2 , TM 3 , TM 4 , TM 5 , TM 6 , TM 7 , and TM 8  will be described in further detail. 
     The eight shafts TM 1 , TM 2 , TM 3 , TM 4 , TM 5 , TM 6 , TM 7 , and 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 . The eight shafts TM 1 , TM 2 , TM 3 , TM 4 , TM 5 , TM 6 , TM 7 , and TM 8  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 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. 
     The first shaft TM 1  directly connects the first rotational element N 1  (first sun gear S 1 ) with the sixth rotational element N 6  (second ring gear R 2 ), the eighth rotational element N 8  (third planet carrier PC 3 ), and the tenth rotational element N 10  (fourth sun gear S 4 ). 
     The second shaft TM 2  is directly connected to the second rotational element N 2  (first planet carrier PC 1 ) and is directly connected to the input shaft IS so as to be operated as an input element continuously. 
     The third shaft TM 3  directly connects the third rotational element N 3  (first ring gear R 1 ) with the seventh rotational element N 7  (third sun gear S 3 ). 
     The fourth shaft TM 4  is connected to the fourth rotational element N 4  (second sun gear S 2 , and is selectively connected to the second shaft TM 2  so as to be operated as a selective input element or is connected to the transmission housing H so as to be operated as a selective fixed element. 
     Herein, the fourth shaft TM 4  is selectively connected to the transmission housing H in a state of not being connected to the second shaft TM 2 . 
     The fifth shaft TM 5  is connected to the fifth rotational element N 5  (second planet carrier PC 2 ), and is selectively connected to the second shaft TM 2  so as to be operated as a selective input element or is selectively connected to the transmission housing H so as to be operated as a selective fixed element. 
     Herein, the fifth shaft TM 5  is selectively connected to the transmission housing H in a state of not being connected to the second shaft TM 2 . 
     The sixth shaft TM 6  is connected to ninth rotational element N 9  (third ring gear R 3 ) and is selectively connected to the fifth shaft TM 5 . 
     The seventh shaft TM 7  is connected to the eleventh rotational element N 11  (fourth planet carrier PC 4 ), is selectively connected to the third shaft TM 3 , and is directly connected to the output shaft OS so as to be continuously connected to an output element. 
     The eighth shaft TM 8  is connected to the twelfth rotational element N 12  (fourth ring gear R 4 ) and is selectively connected to the transmission housing H so as to be operated as a selective fixed element. 
     In addition, four clutches C 1 , C 2 , C 3 , and C 4  are disposed at portions at which any two shafts among the eight shafts TM 1 , TM 2 , TM 3 , TM 4 , TM 5 , TM 6 , TM 7 , and TM 8  including the input shaft IS and the output shaft OS are selectively connected to each other. 
     In addition, three brakes B 1 , B 2 , and B 3  are disposed at portions at which any one shaft among the eight shafts TM 1 , TM 2 , TM 3 , TM 4 , TM 5 , TM 6 , TM 7 , and TM 8  is selectively connected to the transmission housing H. 
     Arrangements of the four clutches C 1 , C 2 , C 3 , and C 4  and the three brakes B 1 , B 2 , and B 3  are described in detail. 
     The first clutch C 1  is disposed between the third shaft TM 3  and the seventh shaft TM 7  or the output shaft OS and selectively connects the third shaft TM 3  with the seventh shaft TM 7  or the output shaft OS. 
     The second clutch C 2  is disposed between the second shaft TM 2  and the fourth shaft TM 4  and selectively connects the second shaft TM 2  with the fourth shaft TM 4 . 
     The third clutch C 3  is disposed between the second shaft TM 2  and the fifth shaft TM 5  and selectively connects the second shaft TM 2  with the fifth shaft TM 5 . 
     The fourth clutch C 4  is disposed between the fifth shaft TM 5  and the sixth shaft TM 6  and selectively connects the fifth shaft TM 5  with the sixth shaft TM 6 . 
     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. 
     The second brake B 2  is disposed between the fifth shaft TM 5  and the transmission housing H and selectively connects the fifth shaft TM 5  with the transmission housing H. 
     The third brake B 3  is disposed between the eighth shaft TM 8  and the transmission housing H and selectively connects the eighth shaft TM 8  with the transmission housing H. 
     As shown in  FIG. 1  that the second clutch C 2  and the third clutch C 3  selectively connect the second shaft TM 2  with the fourth shaft TM 4  and the second shaft TM 2  with the fifth shaft TM 5 , respectively. Since the second shaft TM 2  is directly connected to the input shaft IS, the second clutch C 2  can selectively connect the input shaft IS with the fourth shaft TM 4  and the third clutch C 3  can selectively connect the input shaft IS with the fifth shaft TM 5 . 
     The second clutch C 2  and the first brake B 1  selectively connect the fourth shaft TM 4  with the second shaft TM 2  directly connected to the input shaft IS and the transmission housing H, respectively. Therefore, both of the second clutch C 2  and the first brake B 1  are not simultaneously operated at each speed stage. 
     In addition, the third clutch C 3  and the second brake B 2  selectively connect the fifth shaft TM 5  with the second shaft TM 2  directly connected to the input shaft IS and the transmission housing H, respectively. Therefore, both of the third clutch C 3  and the second brake B 2  are not simultaneously operated at each speed stage. 
     The control elements including the first, second, third, and fourth clutches C 1 , C 2 , C 3 , and C 4  and the first, second, and third brakes B 1 , B 2 , and B 3  may be multi-plates friction elements of wet type that are operated by hydraulic pressure. 
       FIG. 2  is an operation chart of control elements at each speed stage in the planetary gear train according to the first embodiment of the present disclosure. 
     As shown in  FIG. 2 , three control elements among the first, second, third, and fourth clutches C 1 , C 2 , C 3 , and C 4  and the first, second, and third brakes B 1 , B 2 , and B 3  are operated at each speed stage in the planetary gear train according to the first embodiment of the present disclosure. The first embodiment of the present disclosure can achieve one reverse speed stage and ten forward speed stages and shifting processes will be described in detail. 
     The second and third brakes B 2  and B 3  and the fourth clutch C 4  are simultaneously operated at a first forward speed stage D 1 . 
     In a state that the fifth shaft TM 5  is connected to the sixth shaft TM 6  by operation of the fourth clutch C 4 , the torque of the input shaft IS is input to the second shaft TM 2 . In addition, the fifth shaft TM 5  and the eighth shaft TM 8  are operated as the fixed elements by operation of the second and third brakes B 2  and B 3 . Therefore, the torque of the input shaft IS is shifted into the first forward speed stage, and the first forward speed stage is output through the output shaft OS connected to the seventh shaft TM 7 . 
     The first and third brakes B 1  and B 3  and the fourth clutch C 4  are simultaneously operated at a second forward speed stage D 2 . 
     In a state that the fifth shaft TM 5  is connected to the sixth shaft TM 6  by operation of the fourth clutch C 4 , the torque of the input shaft IS is input to the second shaft TM 2 . In addition, the fourth shaft TM 4  and the eighth shaft TM 8  are operated as the fixed elements by operation of the first and third brakes B 1  and B 3 . Therefore, the torque of the input shaft IS is shifted into the second forward speed stage, and the second forward speed stage is output through the output shaft OS connected to the seventh shaft TM 7 . 
     The third brake B 3  and the third and fourth clutches C 3  and C 4  are simultaneously operated at a third forward speed stage D 3 . 
     In a state that the second shaft TM 2  is connected to the fifth shaft TM 5  by operation of the third clutch C 3  and the fifth shaft TM 5  is connected to the sixth shaft TM 6  by operation of the fourth clutch C 4 , the torque of the input shaft IS is input to the second shaft TM 2  and the fifth shaft TM 5 . In addition, the eighth shaft TM 8  is operated as the fixed element by operation of the third brake B 3 . Therefore, the torque of the input shaft IS is shifted into the third forward speed stage, and the third forward speed stage is output through the output shaft OS connected to the seventh shaft TM 7 . 
     The first and third brakes B 1  and B 3  and the third clutch C 3  are simultaneously operated at a fourth forward speed stage D 4 . 
     In a state that the second shaft TM 2  is connected to the fifth shaft TM 5  by operation of the third clutch C 3 , the torque of the input shaft IS is input to the second shaft TM 2  and the fifth shaft TM 5 . In addition, the fourth shaft TM 4  and the eighth shaft TM 8  are operated as the fixed elements by operation of the first and third brakes B 1  and B 3 . Therefore, the torque of the input shaft IS is shifted into the fourth forward speed stage, and the fourth forward speed stage is output through the output shaft OS connected to the seventh shaft TM 7 . 
     The first and third brakes B 1  and B 3  and the first clutch C 1  are simultaneously operated at a fifth forward speed stage D 5 . 
     In a state that the third shaft TM 3  is connected to the seventh shaft TM 7  by operation of the first clutch C 1 , the torque of the input shaft IS is input to the second shaft TM 2 . In addition, the fourth shaft TM 4  and the eighth shaft TM 8  are operated as the fixed elements by operation of the first and third brakes B 1  and B 3 . Therefore, the torque of the input shaft IS is shifted into the fifth forward speed stage, and the fifth forward speed stage is output through the output shaft OS connected to the seventh shaft TM 7 . 
     The first brake B 1  and the first and third clutches C 1  and C 3  are simultaneously operated at a sixth forward speed stage D 6 . 
     In a state that the third shaft TM 3  is connected to the seventh shaft TM 7  by operation of the first clutch C 1  and the second shaft TM 2  is connected to the fifth shaft TM 5  by operation of the third clutch C 3 , the torque of the input shaft IS is input to the second shaft TM 2  and the fifth shaft TM 5 . In addition, the fourth shaft TM 4  is operated as the fixed element by operation of the first brake B 1 . Therefore, the torque of the input shaft IS is shifted into the sixth forward speed stage, and the sixth forward speed stage is output through the output shaft OS connected to the seventh shaft TM 7 . 
     The first, third, and fourth clutches C 1 , C 3 , and C 4  are simultaneously operated at a seventh forward speed stage D 7 . 
     In a state that the third shaft TM 3  is connected to the seventh shaft TM 7  by operation of the first clutch C 1 , the second shaft TM 2  is connected to the fifth shaft TM 5  by operation of the third clutch C 3 , and the fifth shaft TM 5  is connected to the sixth shaft TM 6  by operation of the fourth clutch C 4 , the torque of the input shaft IS is input to the second shaft TM 2  and the fifth shaft TM 5 . Therefore, all the planetary gear sets become lock-up states, thereby the torque of the input shaft IS being shifted into the seventh forward speed stage, and the seventh forward speed stage being output through the output shaft OS connected to the seventh shaft TM 7 . 
     The second brake B 2  and the first and fourth clutches C 1  and C 4  are simultaneously operated at an eighth forward speed stage D 8 . 
     In a state that the third shaft TM 3  is connected to the seventh shaft TM 7  by operation of the first clutch C 1  and the fifth shaft TM 5  is connected to the sixth shaft TM 6  by operation of the fourth clutch C 4 , the torque of the input shaft IS is input to the second shaft TM 2 . In addition, the fifth shaft TM 5  is operated as the fixed element by operation of the second brake B 2 . Therefore, the torque of the input shaft IS is shifted into the eighth forward speed stage, and the eighth forward speed stage is output through the output shaft OS connected to the seventh shaft TM 7 . 
     The first and second brakes B 1  and B 2  and the first clutch C 1  are simultaneously operated at a ninth forward speed stage D 9 . 
     In a state that the third shaft TM 3  is connected to the seventh shaft TM 7  by operation of the first clutch C 1 , the torque of the input shaft IS is input to the second shaft TM 2 . In addition, the fourth shaft TM 4  and the fifth shaft TM 5  are operated as the fixed elements by operation of the first and second brakes B 1  and B 2 . Therefore, the torque of the input shaft IS is shifted into the ninth forward speed stage, and first, second brake B 1  and B 2  is output through the output shaft OS connected to the seventh shaft TM 7 . 
     The second brake B 2  and the first and second clutches C 1  and C 2  are simultaneously operated at a tenth forward speed stage D 10 . 
     In a state that the third shaft TM 3  is connected to the seventh shaft TM 7  by operation of the first clutch C 1  and the second shaft TM 2  is connected to the fourth shaft TM 4  by operation of the second clutch C 2 , the torque of the input shaft IS is input to the second shaft TM 2  and the fourth shaft TM 4 . In addition, the fifth shaft TM 5  is operated as the fixed element by operation of the second brake B 2 . Therefore, the torque of the input shaft IS is shifted into the tenth forward speed stage, and the tenth forward speed stage is output through the output shaft OS connected to the seventh shaft TM 7 . 
     The second and third brakes B 2  and B 3  and the second clutch C 2  are simultaneously operated at a reverse speed stage REV. 
     In a state that the second shaft TM 2  is connected to the fourth shaft TM 4  by operation of the second clutch C 2 , the torque of the input shaft IS is input to the second shaft TM 2  and the fourth shaft TM 4 . In addition, the fifth shaft TM 5  and the eighth shaft TM 8  are operated as the fixed elements by operation of the second and third brakes B 2  and B 3 . Therefore, the torque of the input shaft IS is shifted into the reverse speed stage, and the reverse speed stage is output through the output shaft OS connected to the seventh shaft TM 7  as an inverse rotation speed. 
     The planetary gear trains according to the first embodiment of the present disclosure may achieve at least ten 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 four clutches C 1 , C 2 , C 3 , and C 4  and the three brakes B 1 , B 2 , and B 3 . 
     In addition, since a gear ratio span greater than 10.53 is secured, driving efficiency of the engine may be increased. 
     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. 
       FIG. 3  is a schematic diagram of a planetary gear train according to the second embodiment of the present disclosure. 
     Referring to  FIG. 1 , the first, second, third, and fourth planetary gear sets are disposed in a sequence of the second, third, first, and fourth planetary gear sets PG 2 , PG 3 , PG 1 , and PG 4  from the engine according to the first embodiment, but, as shown in  FIG. 3 , the first, second, third, and fourth planetary gear sets are disposed in a sequence of the second, third, fourth, and first planetary gear trains PG 2 , PG 3 , PG 4 , and PG 1  from the engine according to the second embodiment. 
     The connections of the shafts and the transmission housing according to the second embodiment are the same as those according to the first embodiment but arrangements of the planetary gear sets according to the second embodiment are different from those according to the first embodiment. The shifting processes of the second embodiment are the same as those of the first embodiment. 
     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.