Patent Publication Number: US-10316936-B2

Title: Planetary gear train of automatic transmission for vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2016-0170766, filed on Dec. 14, 2016, which is incorporated herein by reference in its entirety. 
     FIELD 
     The present disclosure relates to 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. 
     Recently, increase of oil price leads more competition for improving fuel efficiency of a vehicle. 
     In this sense, research on an automatic transmission has been performed to simultaneously provide better drivability and fuel consumption by achieving more shift stages. 
     In order to achieve more shift stages for an automatic transmission, the number of parts is typically increased, which may deteriorate installability, production cost, weight and/or power flow efficiency. 
     Therefore, in order to enhance fuel efficiency of an automatic transmission through more shift stages with reduced number of components, a planetary gear train for an automatic transmission enabling more shift-stages has been developed. 
     We have discovered that since an automatic transmission for eight or more shift-stages typically includes three to four planetary gear sets and five to six engagement elements (frictional elements), and the transmission may easily become lengthy, thereby deteriorating installability. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the present 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. 
     SUMMARY 
     The present disclosure provides a planetary gear train of an automatic transmission for a vehicle having advantages of realizing at least nine forward speeds and at least one reverse speed by a combination of four planetary gear sets, two external gears and six engagement elements, thereby providing improvement of power delivery performance and fuel consumption and improving installability by reducing a length. 
     In addition, a wide available range of varying gear teeth of transfer gears enables easily obtaining desired gear ratios for respective vehicles, thereby improving power delivery performance and fuel consumption. 
     In one form of the present disclosure, a planetary gear train includes: first, second, third, and fourth planetary gear sets, first and second externally-engaged gear sets, an input shaft, and an output shaft. The first planetary gear set forms first, second, and third rotational elements. The second planetary gear set forms fourth, fifth, and sixth rotational elements. The third planetary gear set forms seventh, eighth, and ninth rotational elements. The fourth planetary gear set forms tenth, eleventh, and twelfth rotational elements. The first externally-engaged gear set forms thirteenth and fourteenth rotational elements. The second externally-engaged gear set forms fifteenth and sixteenth rotational elements. The input shaft is disposed coaxial with the first, second, and third planetary gear sets. The output shaft is disposed in parallel with the input shaft and coaxial with the fourth planetary gear set. The first rotational element and the seventh rotational element are connected with the tenth rotational element through the second externally-engaged gear set. The second rotational element is fixedly connected with the input shaft. The twelfth rotational element is selectively connected with a transmission housing. The third rotational element is selectively externally-engaged with the eleventh rotational element that is fixedly connected with the output shaft. 
     The exemplary gear train may further include first to tenth shafts. The first shaft may be fixedly connected with the first rotational element and the seventh rotational element. The second shaft may be fixedly connected with the second rotational element, the fifth rotational element, and the input shaft. The third shaft may be fixedly connected with the third rotational element and connected with the thirteenth rotational element. The fourth shaft may be fixedly connected with the fourth rotational element and fixedly connected with the transmission housing. The fifth shaft may be fixedly connected with the sixth rotational element. The sixth shaft may be fixedly connected with the eighth rotational element and selectively connected with the fifth shaft. The seventh shaft may be fixedly connected with the ninth rotational element, selectively connected with the fifth shaft, and selectively connected with the transmission housing. The eighth shaft may be fixedly connected with the tenth rotational element and externally gear-meshed with the first shaft. The ninth shaft may be fixedly connected with the eleventh rotational element, selectively externally-engaged with the third shaft, and fixedly connected with the output shaft. The tenth shaft may be fixedly connected with the twelfth rotational element and selectively connected with the transmission housing. 
     In an exemplary form, two shafts among the first shaft, the sixth shaft, and the seventh shaft may be selectively interconnected, such that the third planetary gear set integrally rotate when the two shafts are connectedly operated. 
     An exemplary gear train may further include: a first clutch arranged between the second shaft and the seventh shaft, a second clutch arranged between the first shaft and the sixth shaft, a third clutch arranged between the ninth shaft and the fourteenth rotational element, a fourth clutch arranged between the fifth shaft and the sixth shaft, a first brake arranged between the seventh shaft and the transmission housing, and a second brake arranged between the tenth shaft and the transmission housing. 
     In one form, an gear train may further include: a first clutch arranged between the second shaft and the seventh shaft, a second clutch arranged between the first shaft and the seventh shaft, a third clutch arranged between the ninth shaft and the fourteenth rotational element, a fourth clutch arranged between the fifth shaft and the sixth shaft, a first brake arranged between the seventh shaft and the transmission housing, and a second brake arranged between the tenth shaft and the transmission housing. 
     In another form, an exemplary gear train may further include: a first clutch arranged between the second shaft and the seventh shaft, a second clutch arranged between the sixth shaft and the seventh shaft, a third clutch arranged between the ninth shaft and the fourteenth rotational element, a fourth clutch arranged between the fifth shaft and the sixth shaft, a first brake arranged between the seventh shaft and the transmission housing, and a second brake arranged between the tenth shaft and the transmission housing. 
     An exemplary gear train may further include: a first clutch arranged between the second shaft and the seventh shaft, a second clutch arranged between the first shaft and the sixth shaft, a third clutch arranged between the third shaft and the thirteenth rotational element, a fourth clutch arranged between the fifth shaft and the sixth shaft, a first brake arranged between the seventh shaft and the transmission housing, and a second brake arranged between the tenth shaft and the transmission housing. 
     An exemplary gear train may further include: a first clutch arranged between the second shaft and the seventh shaft, a second clutch arranged between the first shaft and the seventh shaft, a third clutch arranged between the third shaft and the thirteenth rotational element, a fourth clutch arranged between the fifth shaft and the sixth shaft, a first brake arranged between the seventh shaft and the transmission housing, and a second brake arranged between the tenth shaft and the transmission housing. 
     An exemplary gear train may further include: a first clutch arranged between the second shaft and the seventh shaft, a second clutch arranged between the sixth shaft and the seventh shaft, a third clutch arranged between the third shaft and thirteenth rotational element, a fourth clutch arranged between the fifth shaft and the sixth shaft, a first brake arranged between the seventh shaft and the transmission housing, and a second brake arranged between the tenth shaft and the transmission housing. 
     The first planetary gear set may include: a first sun gear as the first rotational element, a first planet carrier as the second rotational element, and a first ring gear as the third rotational element. The second planetary gear set may include a second sun gear as the fourth rotational element, a second planet carrier as the fifth rotational element, and a second ring gear as the sixth rotational element. The third planetary gear set may include a third sun gear as the seventh rotational element, a third planet carrier as the eighth rotational element, and a third ring gear as the ninth rotational element. The fourth planetary gear set may include a fourth sun gear as the tenth rotational element, a fourth planet carrier as the eleventh rotational element, and a fourth ring gear as the twelfth rotational element. 
     The first planetary gear set may be a single pinion planetary gear set. The second planetary gear set may be a double pinion planetary gear set. The third planetary gear set may be a double pinion planetary gear set. The fourth planetary gear set may be a single pinion planetary gear set. 
     According to a planetary gear train according to an exemplary form of the present disclosure, planetary gear sets are dividedly arranged on input and output shafts disposed in parallel, thereby reducing a length and improving installability. 
     According to a planetary gear train according to an exemplary form of the present disclosure, at least eight forward speeds and at least one reverse speed may be realized by employing two externally engaged transfer gears in addition to a combination of planetary gear sets, thereby providing a wide range of varying gear teeth so as to easily achieve desired gear ratio and to easily comply with desired performance for respective vehicles. 
     In addition, according to a planetary gear train according to an exemplary form of the present disclosure, a gear ratio span of more than 9.7 may be achieved while realizing at least nine forward speeds and at least one reverse speed, thereby increasing an engine driving efficiency. 
     In addition, the linearity of step ratios of shift stages is secured while multi-staging the shift stage with high efficiency, thereby making it possible to improve drivability such as acceleration before and after a shift, an engine speed rhythmic sense, and the like. 
     Further, effects that can be obtained or expected from exemplary forms of the present disclosure are directly or suggestively described in the following detailed description. That is, various effects expected from exemplary forms of the present disclosure will be described in the following detailed description. 
     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 according to a first exemplary form of the present disclosure; 
         FIG. 2  is an operational chart for respective engagement elements at respective shift-stages in a planetary gear train according to a first exemplary form of the present disclosure; 
         FIG. 3  is a schematic diagram of a planetary gear train according to a second exemplary form of the present disclosure; 
         FIG. 4  is a schematic diagram of a planetary gear train according to a third exemplary form of the present disclosure; 
         FIG. 5  is a schematic diagram of a planetary gear train according to a fourth exemplary form of the present disclosure; 
         FIG. 6  is a schematic diagram of a planetary gear train according to a fifth exemplary form of the present disclosure; 
         FIG. 7  is a schematic diagram of a planetary gear train according to a sixth exemplary form of the present disclosure; 
         FIG. 8  is a schematic diagram of a planetary gear train according to a seventh exemplary form of the present disclosure; 
         FIG. 9  is a schematic diagram of a planetary gear train according to an eighth exemplary form of the present disclosure; 
         FIG. 10  is a schematic diagram of a planetary gear train according to a ninth exemplary form of the present disclosure; 
         FIG. 11  is a schematic diagram of a planetary gear train according to a tenth exemplary form of the present disclosure; 
         FIG. 12  is a schematic diagram of a planetary gear train according to a eleventh exemplary form of the present disclosure; and 
         FIG. 13  is a schematic diagram of a planetary gear train according to a twelfth exemplary form 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. 
     DETAILED DESCRIPTION 
     The present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary forms of the present disclosure are shown. As those skilled in the art would realize, the described forms may be modified in various different ways, all without departing from the spirit or scope of the present disclosure. 
     The drawings and description are to be regarded as illustrative in nature and not restrictive, and like reference numerals designate like elements throughout the specification. 
     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 a first exemplary form of the present disclosure. 
     Referring to  FIG. 1 , a planetary gear train includes: an input shaft IS, an output shaft OS, first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , first and second transfer gears TF 1  and TF 2  as first and second externally-engaged gear sets, and engagement elements of four clutches C 1 , C 2 , C 3 , and C 4  and two brakes B 1  and B 2 . 
     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. 
     The output shaft OS is an output member, and, arranged in parallel with the input shaft IS, outputs a shifted driving torque to a drive shaft through a differential apparatus. 
     The first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3  are arranged at external circumference of the input shaft IS and form a main shifting portion. The first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3  are arranged in the order of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3  from an engine side. 
     The fourth planetary gear set PG 4  is arranged at external circumference of the output shaft OS disposed in parallel with the input shaft IS and forms an auxiliary shifting portion. 
     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 supports first pinion P 1  externally engaged with the first sun gear S 1 , and a first ring gear R 1  that is internally engaged with the first pinion 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 double pinion planetary gear set, and includes a second sun gear S 2 , a second planet carrier PC 2  that rotatably supports a second pinion P 2  externally gear-meshed with the second sun gear S 2 , and a second ring gear R 2  that is internally engaged with the second pinion 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 double pinion planetary gear set, and includes a third sun gear S 3 , a third planet carrier PC 3  that rotatably supports a third pinion P 3  externally gear-meshed with the third sun gear S 3 , and a third ring gear R 3  that is internally engaged with the third pinion 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 S 4 , a fourth planet carrier PC 4  that supports fourth pinion P 4  externally engaged with the fourth sun gear S 4 , and a fourth ring gear R 4  that is internally engaged with the fourth pinion 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, and third planetary gear sets PG 1 , PG 2 , and PG 3 , the first rotational element N 1  is fixedly connected with the seventh rotational element N 7 , the second rotational element N 2  is fixedly connected with the fifth rotational element N 5 , and seven shafts TM 1  to TM 7  are formed. 
     Three shafts TM 8  to TM 10  are connected to the fourth planetary gear set PG 4 . 
     The ten shafts TM 1  to TM 10  are hereinafter described in detail. 
     The first shaft TM 1  is fixedly connected with the first rotational element N 1  (first sun gear S 1 ) and the seventh rotational element N 7  (third sun gear S 3 ). 
     The second shaft TM 2  is fixedly connected with the second rotational element N 2  (first planet carrier PC 1 ) and the fifth rotational element N 5  (second planet carrier PC 2 ), and fixedly connected with the input shaft IS, thereby always acting as an input element. 
     The third shaft TM 3  is fixedly connected with the third rotational element N 3  (first ring gear R 1 ). 
     The fourth shaft TM 4  is fixedly connected with the fourth rotational element N 4  (second sun gear S 2 ), and fixedly connected with the transmission housing H, thereby always acting as a fixed element. 
     The fifth shaft TM 5  is fixedly connected with the sixth rotational element N 6  (second ring gear R 2 ). 
     The sixth shaft TM 6  is connected with the eighth rotational element N 8  (third planet carrier PC 3 ), selectively connected with the fifth shaft TMS, and selectively connected with the first shaft TM 1 . 
     The seventh shaft TM 7  is fixedly connected with the ninth rotational element N 9  (third ring gear R 3 ), selectively connected with the second shaft TM 2 , and selectively connected with the transmission housing H, thereby selectively acting as a fixed element. 
     The eighth shaft TM 8  is fixedly connected with the tenth rotational element N 10  (fourth sun gear S 4 ), and externally gear-meshed with the first shaft TM 1 . 
     The ninth shaft TM 9  is fixedly connected with the eleventh rotational element N 11  (fourth planet carrier PC 4 ), fixedly connected with the output shaft OS thereby always acting as an output element, and selectively gear-meshed with the third shaft TM 3  externally. 
     The tenth shaft TM 10  is fixedly connected with the twelfth rotational element N 12  (fourth ring gear R 4 ), and selectively connected with the transmission housing H, thereby selectively acting as a fixed element. 
     The first and second transfer gears TF 1  and TF 2  formed as externally-engaged gear sets deliver a shifted torque of the main shifting portion having the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3  to the auxiliary shifting portion having the fourth planetary gear set PG 4 . 
     The first transfer gear TF 1  includes a first transfer drive gear TF 1   a  and a first transfer driven gear TF 1   b  that are externally gear-meshed with each other. The first transfer drive gear TF 1   a  acts as a thirteenth rotational element N 13  fixedly connected with the third shaft TM 3 , and the first transfer driven gear TF 1   b  acts as a fourteenth rotational element N 14  fixedly connected with the ninth shaft TM 9 . Thereby, the third shaft TM 3  and the ninth shaft TM 9  are externally gear-meshed with each other through the first transfer gear TF 1 . 
     The second transfer gear TF 2  includes a second transfer drive gear TF 2   a  and a second transfer driven gear TF 2   b  that are externally gear-meshed with each other. The second transfer drive gear TF 2   a  acts as a fifteenth rotational element N 15  fixedly connected with the first shaft TM 1 , and the second transfer driven gear TF 2   b  acts as a sixteenth rotational element N 16  fixedly connected with the eighth shaft TM 8 . Thereby, the first shaft TM 1  and the eighth shaft TM 8  are externally gear-meshed with each other through the second transfer gear TF 2 . 
     As a result, respective shafts externally gear-meshed by the first or second transfer gear TF 1  or TF 2  rotate in opposite directions, and the gear ratios of the first and second transfer gears TF 1  and TF 2  may be preset in consideration of desired speed ratio of the transmission. 
     Each of the eleven shafts TM 1  to TM 11  may be a rotational member that fixedly 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. 
     In the disclosure, when two or more members are described to be “fixedly connected”, where the member may be any of a shaft, an input shaft, an output shaft, a rotational member, and a transmission housing, it means that the fixedly connected members always rotate at a same speed. 
     When two or more members are described to be “selectively connected” by an engagement element, it means that the selectively connected members rotates separately when the engagement element is not engaged, and rotates at a same speed when the engagement element is engaged. 
     The engagement elements include the four clutches C 1 , C 2 , C 3 , and C 4  and the two brakes B 1  and B 2 , and are arranged as follows. 
     The first clutch C 1  is arranged between the second shaft TM 2  and the seventh shaft TM 7 , such that the second shaft TM 2  and the seventh shaft TM 7  may selectively become integral. 
     The second clutch C 2  is arranged between the first shaft TM 1  and the sixth shaft TM 6 , such that the first shaft TM 1  and the sixth shaft TM 6  may selectively become integral. 
     The third clutch C 3  is arranged between the ninth shaft TM 9  and the fourteenth rotational element N 14  of the first transfer gear TF 1 , such that the ninth shaft TM 9  and the fourteenth rotational element N 14  of the first transfer gear TF 1  may selectively become integral. 
     The fourth clutch C 4  is arranged between the fifth shaft TM 5  and the sixth shaft TM 6 , such that the fifth shaft TM 5  and the sixth shaft TM 6  may selectively become integral. 
     The first brake B 1  is arranged between the seventh shaft TM 7  and the transmission housing H, such that the seventh shaft TM 7  may selectively act as a fixed element. 
     The second brake B 2  is arranged between the tenth shaft TM 10  and the transmission housing H, such that the tenth shaft TM 10  may selectively act as a fixed element. 
     The second clutch C 2  enables the third planetary gear set PG 3  to integrally rotate, and for such a purpose the second clutch C 2  is described to selectively connect the first shaft TM 1  and the sixth shaft TM 6 , in the first exemplary form. It will be obviously understood that the same function and result may achieved by selectively connecting two of the seventh, eighth, and ninth rotational elements N 7 , N 8 , and N 9 , or alternatively, by selectively connecting two shafts of the first shaft TM 1 , the sixth shaft TM 6 , and the seventh shaft TM 7 . 
     The engagement elements of the first, second, third, and fourth clutches C 1 , C 2 , C 3 , and C 4  and the first and second brakes B 1  and B 2  may be realized as multi-plate hydraulic pressure friction devices that are frictionally engaged by hydraulic pressure, however, it should not be understood to be limited thereto, since various other configuration that are electrically controllable may be available. 
       FIG. 2  is an operational chart for respective engagement elements at respective shift-stages in a planetary gear train according to a first exemplary form of the present disclosure. 
     Referring to  FIG. 2 , a planetary gear train according to a first exemplary form of the present disclosure realizes shifting by operating three engagement elements among the four clutches C 1 , C 2 , C 3 , and C 4  and the two brakes B 1  and B 2 . 
     [The Forward First Speed] 
     In the forward first speed D 1 , the second and fourth clutches C 2  and C 4  and the second brake B 2  are simultaneously operated. 
     As a result, third planetary gear set PG 3  integrally rotates by the operation of the second clutch C 2 , and the fifth shaft TM 5  is connected with the sixth shaft TM 6  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is input to the second shaft TM 2 . 
     Then, the fourth shaft TM 4  always acts as a fixed element, and the tenth shaft TM 10  acts as a fixed element by the operation of the second brake B 2 , thereby realizing the forward first speed by cooperative operation of respective shafts and outputting a shifted torque to the output shaft OS connected with the ninth shaft TM 9 . 
     [The Forward Second Speed] 
     In the forward second speed D 2 , the first and second clutch C 1  and C 2  and the second brake B 2  are simultaneously operated. 
     As a result, third planetary gear set PG 3  integrally rotates by the operation of the second clutch C 2 , and the second shaft TM 2  is connected with 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 input to the second shaft TM 2 . 
     Then, the fourth shaft TM 4  always acts as a fixed element, and the tenth shaft TM 10  acts as a fixed element by the operation of the second brake B 2 , thereby realizing the forward second speed by cooperative operation of respective shafts and outputting a shifted torque to the output shaft OS connected with the ninth shaft TM 9 . 
     [The Forward Third Speed] 
     In the forward third speed D 3 , the first and 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 with the seventh shaft TM 7  by the operation of the first clutch C 1 , and the fifth shaft TM 5  is connected with the sixth shaft TM 6  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is input to the second shaft TM 2 . 
     Then, the fourth shaft TM 4  always acts as a fixed element, and the tenth shaft TM 10  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 outputting a shifted torque to the output shaft OS connected with the ninth shaft TM 9 . 
     [The Forward Fourth Speed] 
     In the forward fourth speed D 4 , the first and 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 with the seventh shaft TM 7  by the operation of the first clutch C 1 , and the ninth shaft TM 9  is connected with first transfer gear TF 1  by the operation of the third clutch C 3 . In this state, the torque of the input shaft IS is input to the second shaft TM 2 . 
     Then, the fourth shaft TM 4  always acts as a fixed element, and the tenth shaft TM 10  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 outputting a shifted torque to the output shaft OS connected with the ninth shaft TM 9 . 
     In addition, the forward fourth speed D 4  may be realized by simultaneously operating the third and fourth clutches C 3  and C 4  and the second brake B 2 . 
     In this case, the ninth shaft TM 9  is connected with the first transfer gear TF 1  by the operation of the third clutch C 3 , and the fifth shaft TM 5  is connected with the sixth shaft TM 6  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is input to the second shaft TM 2 . 
     Then, the fourth shaft TM 4  always acts as a fixed element, and the tenth shaft TM 10  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 outputting a shifted torque to the output shaft OS connected with the ninth shaft TM 9 . 
     [The Forward Fifth Speed] 
     In the forward fifth speed D 5 , the first, third, and fourth clutches C 1 , C 3 , and C 4  are simultaneously operated. 
     As a result, the second shaft TM 2  is connected with the seventh shaft TM 7  by the operation of the first clutch C 1 , the ninth shaft TM 9  is connected with the first transfer gear TF 1  by the operation of the third clutch C 3 , and the fifth shaft TM 5  is connected with the sixth shaft TM 6  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is input to the second shaft TM 2 . 
     Then, the fourth shaft TM 4  always acts as a fixed element, thereby realizing the forward fifth speed by cooperative operation of respective shafts and outputting a shifted torque to the output shaft OS connected with the ninth shaft TM 9 . 
     [The Forward Sixth Speed] 
     In the forward sixth speed D 6 , the first, second, and third clutches C 1 , C 2 , and C 3  are simultaneously operated. 
     As a result, third planetary gear set PG 3  integrally rotates by the operation of the second clutch C 2 , the second shaft TM 2  is connected with the seventh shaft TM 7  by the operation of the first clutch C 1 , and the ninth shaft TM 9  is connected with first transfer gear TF 1  by the operation of the third clutch C 3 . In this state, the torque of the input shaft IS is input to the second shaft TM 2 . 
     Then, the fourth shaft TM 4  always acts as a fixed element, thereby realizing the forward sixth speed by cooperative operation of respective shafts and outputting a shifted torque to the output shaft OS connected with the ninth shaft TM 9 . 
     [The Forward Seventh Speed] 
     In the forward seventh speed D 7 , the second, third, and fourth clutches C 2 , C 3 , and C 4  are simultaneously operated. 
     As a result, third planetary gear set PG 3  integrally rotates by the operation of the second clutch C 2 , the ninth shaft TM 9  is connected with the first transfer gear TF 1  by the operation of the third clutch C 3 , and the fifth shaft TM 5  is connected with the sixth shaft TM 6  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is input to the second shaft TM 2 . 
     Then, the fourth shaft TM 4  always acts as a fixed element, and the fourth shaft TM 4  acts as a fixed element by the operation of the first brake B 1 , thereby realizing the forward seventh speed by cooperative operation of respective shafts and outputting a shifted torque to the output shaft OS connected with the ninth shaft TM 9 . 
     [The Forward Eighth Speed] 
     In the forward eighth speed D 8 , the second and third clutches C 2  and C 3  and the first brake B 1  are simultaneously operated. 
     As a result, third planetary gear set PG 3  integrally rotates by the operation of the second clutch C 2 , and the ninth shaft TM 9  is connected with first transfer gear TF 1  by the operation of the third clutch C 3 . In this state, the torque of the input shaft IS is input to the second shaft TM 2 . 
     Then, the fourth shaft TM 4  always acts as a fixed element, and the seventh shaft TM 7  acts as a fixed element by the operation of the first brake B 1 , thereby realizing the forward eighth speed by cooperative operation of respective shafts and outputting a shifted torque to the output shaft OS connected with the ninth shaft TM 9 . 
     [The Forward Ninth Speed] 
     In the forward ninth speed D 9 , the third and fourth clutches C 3  and C 4  and the first brake B 1  are simultaneously operated. 
     As a result, the ninth shaft TM 9  is connected with the first transfer gear TF 1  by the operation of the third clutch C 3 , and the fifth shaft TM 5  is connected with the sixth shaft TM 6  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is input to the second shaft TM 2 . 
     Then, the fourth shaft TM 4  always acts as a fixed element, and the seventh shaft TM 7  acts as a fixed element by the operation of the first brake B 1 , thereby realizing the forward ninth speed by cooperative operation of respective shafts and outputting a shifted torque to the output shaft OS connected with the ninth shaft TM 9 . 
     [The Reverse Speed] 
     In the reverse speed REV, the fourth clutch C 4  and the first and second brakes B 1  and B 2  are simultaneously operated. 
     As a result, the fifth shaft TM 5  is connected with the sixth shaft TM 6  by the operation of the fourth clutch C 4 . In this state, the torque of the input shaft IS is input to the second shaft TM 2 . 
     Then, the fourth shaft TM 4  always acts as a fixed element, and the seventh shaft and the tenth shaft TM 7  and TM 10  acts as a fixed element by the operation of the first and second brakes B 1  and B 2 , thereby realizing the reverse speed by cooperative operation of the shafts and outputting a reverse torque through the output shaft OS connected with the ninth shaft TM 9 . 
       FIG. 2  shows gear ratios calculated under the condition that the gear ratio of the first ring gear R 1 /the first sun gear S 1  is 2.40, the gear ratio of the second ring gear R 2 /the second sun gear S 2  is 2.61, the gear ratio of the third ring gear R 3 /the third sun gear S 3  is 2.22, the gear ratio of the fourth ring gear R 4 /the fourth sun gear S 4  is 2.13, the gear ratio of the first transfer driven gear TF 1   b /the first transfer drive gear TF 1   a  is 1.01, and the gear ratio of the second transfer driven gear TF 2   b /the second transfer drive gear TF 2   a  is 1.01. 
       FIG. 3  is a schematic diagram of a planetary gear train according to a second exemplary form of the present disclosure. 
     In a planetary gear train according to a first exemplary form of the present disclosure shown in  FIG. 1 , the second clutch C 2  enforcing the third planetary gear set PG 3  to integrally rotate is arranged between the first shaft TM 1  and the sixth shaft TM 6 . However, referring to  FIG. 3 , the second clutch C 2  is arranged between the first shaft TM 1  and the seventh shaft TM 7  in a planetary gear train according to a second exemplary form. 
     As a result, the second exemplary form merely differs from a planetary gear train according to a first exemplary form in the location of the second clutch C 2 , and maintains operation and function of the first exemplary form, which is therefore not described in further detail. 
       FIG. 4  is a schematic diagram of a planetary gear train according to a third exemplary form of the present disclosure. 
     In a planetary gear train according to a first exemplary form of the present disclosure shown in  FIG. 1 , the second clutch C 2  enforcing the third planetary gear set PG 3  to integrally rotate is arranged between the first shaft TM 1  and the sixth shaft TM 6 . However, referring to  FIG. 4 , the second clutch C 2  is arranged between the sixth shaft TM 6  and the seventh shaft TM 7  in a planetary gear train according to a third exemplary form. 
     As a result, the third exemplary form merely differs from a planetary gear train according to a first exemplary form in the location of the second clutch C 2 , and maintains operation and function of the first exemplary form, which is therefore not described in further detail. 
       FIG. 5  is a schematic diagram of a planetary gear train according to a fourth exemplary form of the present disclosure. 
     In a planetary gear train according to a first exemplary form of the present disclosure shown in  FIG. 1 , the third clutch C 3  is arranged between the ninth shaft TM 9  and the first transfer gear TF 1 . However, referring to  FIG. 5 , the third clutch C 3  is arranged between the third shaft TM 3  and the first transfer gear TF 1  in a planetary gear train according to a fourth exemplary form. 
     As a result, the fourth exemplary form merely differs from a planetary gear train according to a first exemplary form in the location of the third clutch C 3 , and maintains operation and function of the first exemplary form, which is therefore not described in further detail. 
       FIG. 6  is a schematic diagram of a planetary gear train according to a fifth exemplary form of the present disclosure. 
     In a planetary gear train according to a second exemplary form of the present disclosure shown in  FIG. 3 , the third clutch C 3  is arranged between the ninth shaft TM 9  and the first transfer gear TF 1 . However, referring to  FIG. 6 , the third clutch C 3  is arranged between the third shaft TM 3  and the first transfer gear TF 1  in a planetary gear train according to a fifth exemplary form. 
     As a result, the fifth exemplary form merely differs from a planetary gear train according to a second exemplary form in the location of the third clutch C 3 , and maintains operation and function of the second exemplary form, which is therefore not described in further detail. 
       FIG. 7  is a schematic diagram of a planetary gear train according to a sixth exemplary form of the present disclosure. 
     In a planetary gear train according to a third exemplary form of the present disclosure shown in  FIG. 4 , the third clutch C 3  is arranged between the ninth shaft TM 9  and the first transfer gear TF 1 . However, referring to  FIG. 7 , the third clutch C 3  is arranged between the third shaft TM 3  and the first transfer gear TF 1  in a planetary gear train according to a sixth exemplary form. 
     As a result, the sixth exemplary form merely differs from a planetary gear train according to a third exemplary form in the location of the third clutch C 3 , and maintains operation and function of the third exemplary form, which is therefore not described in further detail. 
       FIG. 8  is a schematic diagram of a planetary gear train according to a seventh exemplary form of the present disclosure. 
     In a planetary gear train according to a first exemplary form of the present disclosure shown in  FIG. 1 , the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3  are arranged in the order of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3  from an engine side. However, in a planetary gear train according to a seventh exemplary form as illustrated in  FIG. 8 , the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3  are arranged in the order of the first, third, second planetary gear sets PG 1 , PG 3 , and PG 2  from the engine side. 
     As a result, the seventh exemplary form merely differs from a planetary gear train according to a first exemplary form in the location of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 , and maintains operation and function of the first exemplary form, which is therefore not described in further detail. 
       FIG. 9  is a schematic diagram of a planetary gear train according to an eighth exemplary form of the present disclosure. 
     In a planetary gear train according to a seventh exemplary form of the present disclosure shown in  FIG. 8 , the second clutch C 2  enforcing third planetary gear set PG 3  to integrally rotate is arranged between the first shaft TM 1  and the sixth shaft TM 6 . However, referring to  FIG. 9 , the second clutch C 2  is arranged between the first shaft TM 1  and the seventh shaft TM 7  in a planetary gear train according to an eighth exemplary form. 
     As a result, the eighth exemplary form merely differs from a planetary gear train according to a seventh exemplary form in the location of the second clutch C 2 , and maintains operation and function of the seventh exemplary form, which is therefore not described in further detail. 
       FIG. 10  is a schematic diagram of a planetary gear train according to a ninth exemplary form of the present disclosure. 
     In a planetary gear train according to a seventh exemplary form of the present disclosure shown in  FIG. 8 , the second clutch C 2  enforcing third planetary gear set PG 3  to integrally rotate is arranged between the first shaft TM 1  and the sixth shaft TM 6 . However, referring to  FIG. 10 , the second clutch C 2  is arranged between the sixth shaft TM 6  and the seventh shaft TM 7  in a planetary gear train according to the ninth exemplary form. 
     As a result, the ninth exemplary form merely differs from a planetary gear train according to a seventh exemplary form in the location of the second clutch C 2 , and maintains operation and function of the seventh exemplary form, which is therefore not described in further detail. 
       FIG. 11  is a schematic diagram of a planetary gear train according to a tenth exemplary form of the present disclosure. 
     In a planetary gear train according to a seventh exemplary form of the present disclosure shown in  FIG. 8 , the third clutch C 3  is arranged between the ninth shaft TM 9  and the first transfer gear TF 1 . However, referring to  FIG. 11 , the third clutch C 3  is arranged between the first transfer gear TF 1  and the third shaft TM 3  in a planetary gear train according to the tenth exemplary form. 
     As a result, the tenth exemplary form merely differs from a planetary gear train according to a seventh exemplary form in the location of the third clutch C 3 , and maintains operation and function of the seventh exemplary form, which is therefore not described in further detail. 
       FIG. 12  is a schematic diagram of a planetary gear train according to an eleventh exemplary form of the present disclosure. 
     In a planetary gear train according to an eighth exemplary form of the present disclosure shown in  FIG. 9 , the third clutch C 3  is arranged between the ninth shaft TM 9  and the first transfer gear TF 1 . However, referring to  FIG. 12 , the third clutch C 3  is arranged between the first transfer gear TF 1  and the third shaft TM 3  in a planetary gear train according to an eleventh exemplary form. 
     As a result, the eleventh exemplary form merely differs from a planetary gear train according to an eighth exemplary form in the location of the third clutch C 3 , and maintains operation and function of the eighth exemplary form, which is therefore not described in further detail. 
       FIG. 13  is a schematic diagram of a planetary gear train according to a twelfth exemplary form of the present disclosure. 
     In a planetary gear train according to a ninth exemplary form of the present disclosure shown in  FIG. 10 , the third clutch C 3  is arranged between the ninth shaft TM 9  and the first transfer gear TF 1 . However, referring to  FIG. 13 , the third clutch C 3  is arranged between the first transfer gear TF 1  and the third shaft TM 3  in a planetary gear train according to the twelfth exemplary form. 
     As a result, the twelfth exemplary form merely differs from a planetary gear train according to a ninth exemplary form in the location of the third clutch C 3 , and maintains operation and function of the ninth exemplary form, which is therefore not described in further detail. 
     As described above, according to a planetary gear train according to an exemplary form of the present disclosure, at least nine forward speeds and at least one reverse speed may be realized by a combination of four planetary gear sets, two transfer gears, and five or six engagement elements, thereby providing improvement of power delivery performance and fuel consumption and improving installability by shortening the length of an automatic transmission. 
     In addition, according to a planetary gear train according to an exemplary form of the present disclosure, two transfer gears of external gears arranged on the output shaft OS are employed in addition to three planetary gear sets, and thus, gear teeth may be widely varied so as to easily achieve desired gear ratio and to easily comply with desired performance for respective vehicles. 
     In addition, according to a planetary gear train according to an exemplary form of the present disclosure, a gear ratio span of more than 8.7 may be achieved while realizing at least nine forward speeds and at least one reverse speed, thereby increasing an engine driving efficiency. 
     In addition, the linearity of step ratios of shift stages is secured while multi-staging the shift stage with high efficiency, thereby making it possible to improve drivability such as acceleration before and after a shift, an engine speed rhythmic sense, and the like. 
     While this present disclosure has been described in connection with what is presently considered to be practical exemplary forms, it is to be understood that the present 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. 
     DESCRIPTION OF SYMBOLS 
     
         
         
           
             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 
             B 1 , B 2 : first and second brakes 
             C 1 , C 2 , C 3 , C 4 : first, second, third, and fourth clutches 
             TF 1 , TF 2 : first and second transfer gears 
             TM 1 , TM 2 , TM 3 , TM 4 , TMS, TM 6 , TM 7 , TM 8 , TM 9 , TM 10 : first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth shafts