Abstract:
The present disclosure provides a planetary gear train of an automatic transmission for a vehicle including an input shaft, an output shaft, four planetary gear sets respectively having three rotational elements, and six control elements for selectively interconnecting the rotational elements and a transmission housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2016-0118080 filed on Sep. 13, 2016, which is incorporated herein by reference in its entirety. 
     FIELD 
     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. 
     In the field of an automatic transmission, more multiplicity of shift-stages is used to enhance fuel efficiency and drivability of a vehicle. The increase of oil price makes it difficult to improve fuel consumption of a vehicle. 
     The engine downsizing has been attempted for purposes of weight reduction and fuel efficiency. Simultaneously, the development of more shift stages of an automatic transmission has caused to provide the enhanced driving stability and fuel efficiency. 
     For more shift-stages of an automatic transmission, the number of parts is typically increased, which may affect installability, production cost, weight and/or power flow efficiency. 
     In that aspect, less number of parts is desired to enhance fuel efficiency of an automatic transmission having more shift-stages. 
     An eight-speed automatic transmission has been introduced recently and a planetary gear train for an automatic transmission enabling more shift-stages is under development. 
     An automatic transmission of eight or more shift-stages typically includes three to four planetary gear sets and five to seven control elements (frictional elements), and this may largely affect the weight of the vehicle. 
     In this regard, disposing planetary gear sets in parallel or employing dog clutches instead of wet-type control elements has been attempted. However, such an arrangement may not be widely applicable, and using dog clutches may easily deteriorate shift-feel. 
     SUMMARY 
     The present disclosure provides a planetary gear train of an automatic transmission for a vehicle having shift-stages of ten forward speeds and one reverse speed by less number of parts, thereby improving power delivery performance and fuel consumption by multi-stages of an automatic transmission, as well as driving stability of a vehicle by utilizing a low rotation speed of an engine. 
     A planetary gear train according to one form of the present disclosure includes an input shaft configured to receive an engine torque; an output shaft configured to output a shifted torque; a first planetary gear set having a first, a second, and a third rotational elements; a second planetary gear set having a fourth, a fifth, and a sixth rotational elements; a third planetary gear set having a seventh, an eighth, and a ninth rotational elements; a fourth planetary gear set having a tenth, an eleventh, and a twelfth rotational elements; a first shaft connected to the first rotational element and the fourth rotational element; a second shaft connected to the second rotational element and connected to the input shaft; a third shaft connected to the third rotational element and the seventh rotational element; a fourth shaft connected to the fifth rotational element and the eighth rotational element, the twelfth rotational element; a fifth shaft connected to the sixth rotational element; a sixth shaft connected to the ninth rotational element; a seventh shaft connected to the tenth rotational element, and selectively connected to the second shaft, the third shaft, and the sixth shaft respectively; and an eighth shaft connected to the eleventh rotational element, selectively connected to the sixth shaft, and connected to the output shaft. 
     The first shaft and the fifth shaft may be selectively connected to a transmission housing respectively. 
     The first, the second, and the 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, the fifth, and the 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, the eighth, and the 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. The tenth, the eleventh, and the 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. 
     The first, the second, the third, and the fourth planetary gear sets may be arranged in an order of the first, the second, the third, and the fourth from an engine side. 
     A planetary gear train according to one form of the present disclosure may further include a first clutch selectively connecting the second shaft and the seventh shaft; a second clutch selectively connecting the third shaft and the seventh shaft; a third clutch selectively connecting the sixth shaft and the eighth shaft; a fourth clutch selectively connecting the sixth shaft and the seventh shaft; a first brake selectively connecting the first shaft and the transmission housing, and a second brake selectively connecting the fifth shaft and the transmission housing. 
     A planetary gear train according to one form of the present disclosure may realize at least ten forward speeds and at least one reverse speed by operating the four planetary gear sets and controlling six control elements. 
     In addition, a planetary gear train according to one form of the present disclosure may improve driving stability when shift-stages become suitable for rotation speed of an engine. 
     Moreover, a planetary gear train according to one form of the present disclosure may increase engine driving efficiency by multi-stages of an automatic transmission, and may further improve power delivery performance and fuel efficiency. 
     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, reference being made to the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a planetary gear train; and 
         FIG. 2  is an operational chart for respective control elements at respective shift-stages in a planetary gear train. 
     
    
    
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
     DETAILED DESCRIPTION 
     The following description is merely one 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 avoid any confusion as the names of the components are identical to one another; thus, an order thereof is not particularly limited. 
       FIG. 1  is a schematic diagram of a planetary gear train according to one form of the present disclosure. 
     Referring to  FIG. 1 , a planetary gear train according to one form of the present disclosure includes a first, a second, a third, and a fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  arranged on a same axis, input shaft IS, output shaft OS, eight shafts TM 1  to TM 8  connected to rotational elements of the first, the second, the third, and the fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , control elements of four clutches C 1  to C 4  and two brakes B 1  and B 2 , and a transmission housing H. 
     Torque taken from the input shaft IS is shifted by cooperative operation of the first, the second, the third, and the fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , and then delivered through the output shaft OS. 
     The planetary gear sets are arranged in the order of the first, the second, the third, and the fourth from an engine side. 
     The input shaft IS is an input member and the torque from a crankshaft of an engine is delivered into the input shaft IS, after being torque-converted through a torque converter. 
     The output shaft OS is an output member, and being arranged on a same axis with the input shaft IS, delivers a shifted driving torque to a drive shaft through a differential apparatus (not shown). 
     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  that rotatably supports a plurality of first pinion gears P 1  externally gear-meshed with the first sun gear S 1 , and a first ring gear R 1  that is internally gear-meshed with the plurality of first pinion gears P 1 . The first sun gear S 1  acts as a first rotational element N 1 , the first planet carrier PC 1  acts as a second rotational element N 2 , and the first ring gear R 1  acts as a third rotational element 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  that rotatably supports a plurality of second pinion gears P 2  externally gear-meshed with the second sun gear S 2 , and second ring gear R 2  that is internally gear-meshed with the plurality of second pinion gears P 2 . The second sun gear S 2  acts as a fourth rotational element N 4 , the second planet carrier PC 2  acts as a fifth rotational element N 5 , and the second ring gear R 2  acts as a sixth rotational element 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  that rotatably supports a plurality of third pinion gears P 3  externally gear-meshed with the third sun gear S 3 , and a third ring gear R 3  that is internally gear-meshed with the plurality of third pinion gears P 3 . The third sun gear S 3  acts as a seventh rotational element N 7 , the third planet carrier PC 3  acts as an eighth rotational element N 8 , and the third ring gear R 3  acts as a ninth rotational element N 9 . 
     The fourth planetary gear set PG 4  is a single pinion planetary gear set, and includes a fourth sun gear  34 , a fourth planet carrier PC 4  that rotatably supports a plurality of fourth pinion gears P 4  externally gear-meshed with the fourth sun gear S 4 , and a fourth ring gear R 4  that is internally gear-meshed with the plurality of fourth pinion gears P 4 . The fourth sun gear S 4  acts as a tenth rotational element N 10 , the fourth planet carrier PC 4  acts as an eleventh rotational element N 11 , and the fourth ring gear R 4  acts as a twelfth rotational element N 12   
     In the arrangement of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , the first rotational element N 1  and the fourth rotational element N 4  are directly connected, the third rotational element N 3  and the seventh rotational element N 7  are directly connected, and fifth rotational element N 5 , the eighth rotational element N 8 , and the twelfth rotational element N 12  are directly connected, respectively, by one of eight shafts TM 1  to TM 8 . 
     The eight shafts TM 1  to TM 8  are arranged as follows. 
     Each of the eight shafts TM 1  to TM 8  may be a rotational member that directly interconnects the input and output shafts and rotational elements of the planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , or may be a rotational member that selectively interconnects a rotational element to the transmission housing H, or may be a fixed member fixed to the transmission housing H. 
     The first shaft TM 1  is connected to the first rotational element N 1  (first sun gear S 1 ) and the fourth rotational element N 4  (second sun gear S 2 ), and selectively connected with the transmission housing H thereby selectively acting as a fixed element. 
     The second shaft TM 2  is connected to the second rotational element N 2  (first planet carrier PC 1 ), and directly connected to the input shaft IS thereby always acting as an input element. 
     The third shaft TM 3  is connected to the third rotational element N 3  (first ring gear R 1 ) and the seventh rotational element N 7  (third sun gear S 3 ). 
     The fourth shaft TM 4  is connected to the fifth rotational element N 5  (second planet carrier PC 2 ), the eighth rotational element N 8  (third planet carrier PC 3 ), and the twelfth rotational element N 12  (fourth ring gear R 4 ). 
     The fifth shaft TM 5  is connected to the sixth rotational element N 6  (second ring gear R 2 ), and selectively connected to the transmission housing H thereby selectively acting as a fixed element. 
     The sixth shaft TM 6  is connected to the ninth rotational element N 9  (third ring gear R 3 ). 
     The seventh shaft TM 7  is connected to the tenth rotational element N 10  (fourth sun gear  34 ), and selectively connected to the second shaft TM 2 , the third shaft TM 3 , and the sixth shaft TM 6  respectively. 
     The eighth shaft TM 8  is connected to the eleventh rotational element N 11  (fourth planet carrier PC 4 ), selectively connected to the sixth shaft TM 6 , and directly connected to the output shaft OS thereby always acting as an output element. 
     The eight shafts TM 1  to TM 8 , the input shaft IS, and the output shaft OS may be selectively interconnected to one another by control elements of four clutches C 1 , C 2 , C 3 , and C 4 . 
     The eight shafts TM 1  to TM 8  may be selectively connected to the transmission housing H, by control elements of two brakes B 1  and B 2 . 
     The four clutches C 1  to C 4  and the two brakes B 1  and B 2  are arranged as follows. 
     The first clutch C 1  is arranged between the second shaft TM 2  and the seventh shaft TM 7 , and selectively connects the second shaft TM 2  and the seventh shaft TM 7 , thereby controlling power delivery therebetween. 
     The second clutch C 2  is arranged 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 , thereby controlling power delivery therebetween. 
     The third clutch C 3  is arranged between the sixth shaft TM 6  and the eighth shaft TM 8 , and selectively connects the sixth shaft TM 6  and the eighth shaft TM 8 , thereby controlling power delivery therebetween. 
     The fourth clutch C 4  is arranged between the sixth shaft TM 6  and the seventh shaft TM 7 , and selectively connects the sixth shaft TM 6  and the seventh shaft TM 7 , thereby controlling power delivery therebetween. 
     The first brake B 1  is arranged between the first shaft TM 1  and the transmission housing H, and selectively connects the first shaft TM 1  to the transmission housing H. 
     The second brake B 2  is arranged between the fifth shaft TM 5  and the transmission housing H, and selectively connects the fifth shaft TM 5  to the transmission housing H. 
     The control elements of the first, the second, the third and the fourth clutch C 1 , C 2 , C 3  and C 4  and the first and the secondbrake B 1 , B 2  may be realized as multi-plate hydraulic pressure friction devices that are frictionally engaged by hydraulic pressure. 
       FIG. 2  is an operational chart for respective control elements at respective shift-stages in a planetary gear train according to one form of the present disclosure. 
     Referring to  FIG. 2 , a planetary gear train according to one form of the present disclosure realizes ten forward speeds and one reverse speed by operating three control elements among the first, the second, the third, and the fourth clutches C 1 , C 2 , C 3 , and C 4  and the first and the second brakes B 1  and B 2  at respective shift-stages. 
     In the forward first speed D 1 , the first clutch C 1  and the first and the second brakes B 1  and B 2  are simultaneously operated. 
     As a result, the second shaft TM 2  is connected to the seventh shaft TM 7  by the operation of the first clutch C 1 . In this state, the torque of the input shaft IS is delivered to the second shaft TM 2  and the seventh shaft TM 7 . 
     In addition, the first shaft TM 1  and the fifth shaft TM 5  act as fixed elements by the operation of the first and the second brakes B 1  and B 2 , thereby realizing the forward first speed by cooperative operation of respective shafts and delivering a shifted torque to the output shaft OS connected to the eighth shaft TM 8 . 
     In the forward second speed D 2 , the second clutch C 2  and the first and the second brakes B 1  and B 2  are simultaneously operated. 
     As a result, the third shaft TM 3  is connected to the seventh shaft TM 7  by the operation of the second clutch C 2 . In this state, the torque of the input shaft IS is delivered to the second shaft TM 2 . 
     In addition, the first shaft TM 1  and the fifth shaft TM 5  act as fixed elements by the operation of the first and the second brakes B 1  and B 2 , thereby realizing the forward second speed by cooperative operation of respective shafts and delivering a shifted torque to the output shaft OS connected to the eighth shaft TM 8 . 
     In the forward third speed D 3 , the first and the second clutch C 1  and C 2  and the second brake B 2  are simultaneously operated. 
     As a result, the second shaft TM 2  is connected to the seventh shaft TM 7  by the operation of the first clutch C 1 , and the third shaft TM 3  is connected to the seventh shaft TM 7  by the operation of the second clutch C 2 . In this state, the torque of the input shaft IS is delivered to the second shaft TM 2  and the seventh shaft TM 7 . 
     In addition, the fifth shaft TM 5  acts as a fixed element by the operation of the second brake B 2 , thereby realizing the forward third speed by cooperative operation of respective shafts and delivering a shifted torque to the output shaft OS connected to the eighth shaft TM 8 . 
     In the forward fourth speed D 4 , the second and the third clutches C 2  and C 3  and the second brake B 2  are simultaneously operated. 
     As a result, the third shaft TM 3  is connected to the seventh shaft TM 7  by the operation of the second clutch C 2 , and the sixth shaft TM 6  is connected to the eighth shaft TM 8  by the operation of the third clutch C 3 . In this state, the torque of the input shaft IS is delivered to the second shaft TM 2 . 
     In addition, the fifth shaft TM 5  acts as a fixed element by the operation of the second brake B 2 , thereby realizing the forward fourth speed by cooperative operation of respective shafts and delivering a shifted torque to the output shaft OS connected to the eighth shaft TM 8 . 
     In the forward fifth speed D 5 , the first and the third clutches C 1  and C 3  and the second brake B 2  are simultaneously operated. 
     As a result, the second shaft TM 2  is connected to the seventh shaft TM 7  by the operation of the first clutch C 1 , and the sixth shaft TM 6  is connected to the eighth shaft TM 8  by the operation of the third clutch C 3 . In this state, the torque of the input shaft IS is delivered to the second shaft TM 2  and the seventh shaft TM 7 . 
     In addition, the fifth shaft TM 5  acts as a fixed element by the operation of the second brake B 2 , thereby realizing the forward fifth speed by cooperative operation of respective shafts and delivering a shifted torque to the output shaft OS connected to the eighth shaft TM 8 . 
     In the forward sixth speed D 6 , the first and the fourth clutches C 1  and C 4  and the second brake B 2  are simultaneously operated. 
     As a result, the second shaft TM 2  is connected to the seventh shaft TM 7  by the operation of the first clutch C 1 , and the sixth shaft TM 6  is connected to the seventh shaft TM 7  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is delivered to the second shaft TM 2  and the seventh shaft TM 7 . 
     In addition, the fifth shaft TM 5  acts as a fixed element by the operation of the second brake B 2 , thereby realizing the forward sixth speed by cooperative operation of respective shafts and delivering a shifted torque to the output shaft OS connected to the eighth shaft TM 8 . 
     In the forward seventh speed D 7 , the first, the third, and the fourth clutches C 1  C 3 , and C 4  are simultaneously operated. 
     As a result, the second shaft TM 2  is connected to the seventh shaft TM 7  by the operation of the first clutch C 1 , the sixth shaft TM 6  is connected to the eighth shaft TM 8  by the operation of the third clutch C 3 , and the sixth shaft TM 6  is connected to the seventh shaft TM 7  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is delivered to the second shaft TM 2  and the seventh shaft TM 7 . 
     In this case, the first, second, the third, and the fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  integrally rotate, and a torque is outputted as inputted, thereby forming the forward seventh speed and delivering a shifted torque to the output shaft OS connected to the eighth shaft TM 8 . 
     In the forward eighth speed D 8 , the first and the fourth clutches C 1  and C 4  and the first brake B 1  are simultaneously operated. 
     As a result, the second shaft TM 2  is connected to the seventh shaft TM 7  by the operation of the first clutch C 1 , and the sixth shaft TM 6  is connected to the seventh shaft TM 7  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is delivered to the second shaft TM 2  and the seventh shaft TM 7 . 
     In addition, the first shaft TM 1  acts as a fixed element by the operation of the first brake B 1 , thereby realizing the forward eighth speed, which is an overdrive gear, by cooperative operation of respective shafts and delivering a shifted torque to the output shaft OS connected to the eighth shaft TM 8 . 
     In the forward ninth speed D 9 , the first and the third clutches C 1  and C 3  and the first brake B 1  are simultaneously operated. 
     As a result, the second shaft TM 2  is connected to the seventh shaft TM 7  by the operation of the first clutch C 1 , and the sixth shaft TM 6  is connected to the eighth shaft TM 8  by the operation of the third clutch C 3 . In this state, the torque of the input shaft IS is delivered to the second shaft TM 2  and the seventh shaft TM 7 . 
     In addition, the first shaft TM 1  acts as a fixed element by the operation of the first brake B 1 , thereby realizing the forward ninth speed, which is an overdrive gear, by cooperative operation of respective shafts and delivering a shifted torque to the output shaft OS connected to the eighth shaft TM 8 . 
     In the forward tenth speed D 10 , the third and the fourth clutches C 3  and C 4  and the first brake B 1  are simultaneously operated. 
     As a result, the sixth shaft TM 6  is connected to the eighth shaft TM 8  by the operation of the third clutch C 3 , and the sixth shaft TM 6  is connected to the seventh shaft TM 7  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is delivered to the second shaft TM 2 . 
     In addition, the first shaft TM 1  acts as a fixed element by the operation of the first brake B 1 , thereby realizing the forward tenth speed, which is a highest gear, by cooperative operation of respective shafts and delivering a shifted torque to the output shaft OS connected to the eighth shaft TM 8 . 
     In the reverse speed REV, the fourth clutch C 4  and the first and the second brakes B 1  and B 2  are simultaneously operated. 
     As a result, the sixth shaft TM 6  is connected to the seventh shaft TM 7  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is delivered to the second shaft TM 2 . 
     In addition, the first shaft TM 1  and the fifth shaft TM 5  respectively act as fixed elements by the operation of the first and the second brakes B 1  and B 2 , thereby realizing the reverse speed by cooperative operation of respective shafts and delivering a shifted torque to the output shaft OS connected to the eighth shaft TM 8 . 
     As described above, a planetary gear train according to one form of the present disclosure may realize the forward tenth speed and one reverse speed by operating four planetary gear set PG 1 , PG 2 , PG 3 , and PG 4  by controlling four clutches C 1 , C 2 , C 3 , and C 4  and two brakes B 1  and B 2 . 
     In addition, a planetary gear train according to one form of the present disclosure may improve driving stability when shift-stages become suitable for rotation speed of an engine. 
     Moreover, a planetary gear train according to one form of the present disclosure may increase engine driving efficiency by multi-stages of an automatic transmission, and may further improve power delivery performance and fuel efficiency. 
     The description of the disclosure is merely one 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.