Abstract:
A planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting changed torque, a first planetary gear set including first, second, and third rotation elements, a second planetary gear set including fourth, fifth, and sixth rotation elements, a compound planetary gear set formed by combining third and fourth planetary gear sets and including seventh, eighth, ninth, and tenth rotation elements, a fifth planetary gear set including eleventh, twelfth, and thirteenth rotation elements, and six friction elements disposed between any one rotation element among thirteen rotation elements and another rotation element or the input shaft, or between any one rotation element among the thirteen rotation elements and a transmission housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2014-0180671 filed Dec. 15, 2014, the entire contents of which is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an automatic transmission for a vehicle. More particularly, the present invention relates to a planetary gear train of an automatic transmission for a vehicle which improves power delivery performance and reduces fuel consumption by achieving nine forward speed stages using a minimum number of constituent elements. 
     Description of Related Art 
     In recent years, a rise in oil price causes dashing into unlimited competition for enhancing fuel efficiency. 
     As a result, research into reduction of weight and the enhancement of fuel efficiency through down-sizing is conducted in the case of an engine and research for simultaneously securing operability and fuel efficiency competitiveness through multiple speed stages is conducted in the case of an automatic transmission. 
     However, in the automatic transmission, as the number of speed stages increase, the number of internal components increase, and as a result, mountability, transmission efficiency, and the like may still deteriorate and cost and weight may increase. 
     Accordingly, development of a planetary gear train which may bring about maximum efficiency with a small number of components may be important in order to increase a fuel efficiency enhancement effect through the multi-stages. 
     In this aspect, in recent years, 8 and 9-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. 
     The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
     BRIEF SUMMARY 
     Various aspects of the present invention are directed to providing a planetary gear train of an automatic transmission for a vehicle that implements nine forward speed stages and one reverse speed stage with a minimum configuration and reduces drag torque by minimizing non-operated friction elements while three friction elements operate in respective gear stages to improve power transmission performance and fuel efficiency. 
     According to various aspects of the present invention, a planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting changed torque, a first planetary gear set including first, second, and third rotation elements, a second planetary gear set including fourth, fifth, and sixth rotation elements, a compound planetary gear set formed by combining third and fourth planetary gear sets and including seventh, eighth, ninth, and tenth rotation elements, a fifth planetary gear set including eleventh, twelfth, and thirteenth rotation elements, and six friction elements disposed between any one rotation element among thirteen rotation elements and another rotation element or the input shaft, or between any one rotation element among the thirteen rotation elements and a transmission housing, in which the input shaft may be continuously connected to the fifth rotation element, the output shaft may be continuously connected to the twelfth rotation element, the ninth rotation element may be selectively connected to the input shaft through a first clutch, the tenth rotation element may be continuously connected to the eleventh rotation element, the seventh rotation element may be continuously connected to the sixth rotation element, the seventh rotation element may be selectively connected to the twelfth rotation element so as to achieve a fifth forward speed stage, the eighth rotation element may be selectively connected to the thirteenth rotation element so as to achieve a sixth forward speed stage, an eighth forward speed stage, and a reverse speed stage, and three friction elements among the six friction elements are operated so as to achieve nine forward speed stages and at least one reverse speed stage. 
     The eighth rotation element may be selectively connected to the thirteenth rotation element through a second clutch, two rotation elements among the seventh, eighth, ninth, and tenth rotation elements may be selectively connected to each other through a third clutch, and the seventh rotation element may be selectively connected to the twelfth rotation element through a fourth clutch. 
     The first rotation element may be continuously connected to the fourth rotation element, the second rotation element may be continuously connected to the thirteenth rotation element, the first rotation element may be selectively connected to the transmission housing through a first brake, and the third rotation element may be selectively connected to the transmission housing through a second brake. 
     A sun gear, a planet carrier, and a ring gear of the first planetary gear set may be set as the first, second, and third rotation elements, a sun gear, a planet carrier, and a ring gear of the second planetary gear set may be set as the fourth, fifth, and sixth rotation elements, and a sun gear, a planet carrier, and a ring gear of the fifth planetary gear set may be set as the eleventh, twelfth, and thirteenth rotation elements. 
     The compound planetary gear set may be formed by combining the third and fourth planetary gear sets that are single pinion planetary gear sets, the seventh rotation element may include third and fourth sun gears that are directly connected to each other, the eighth rotation element may include third and fourth planet carriers that are directly connected to each other, the ninth rotation element may include a third ring gear, and the tenth rotation element may include a fourth ring gear. 
     According to various aspects of the present invention, a planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting changed torque, a first planetary gear set including first, second, and third rotation elements, a second planetary gear set including fourth, fifth, and sixth rotation elements, a compound planetary gear set formed by combining third and fourth planetary gear sets and including seventh, eighth, ninth, and tenth rotation elements, a fifth planetary gear set including eleventh, twelfth, and thirteenth rotation elements, a first rotation shaft including the third rotation element, a second rotation shaft including the second and thirteenth rotation elements, a third rotation shaft including the first and fourth rotation elements, a fourth rotation shaft including the fifth rotation element and directly connected to the input shaft, a fifth rotation shaft including the sixth rotation element and the seventh rotation element, a sixth rotation shaft including the eighth rotation element, a seventh rotation shaft including the ninth rotation element, an eighth rotation shaft including the tenth rotation element and the eleventh rotation element, a ninth rotation shaft including the twelfth rotation element and directly connected to the output shaft, a first clutch selectively connecting the fourth rotation shaft to the seventh rotation shaft, a second clutch selectively connecting the second rotation shaft to the sixth rotation shaft, a third clutch connecting any two rotation shafts among the fifth, sixth, seventh, and eighth rotation shafts so as to direct-couple the third and fourth planetary gear sets, a fourth clutch selectively connecting the fifth rotation shaft to the ninth rotation shaft, a first brake selectively connecting the third rotation shaft to a transmission housing, and a second brake selectively connecting the first rotation shaft to the transmission housing. 
     The first, second, third, fourth, and fifth planetary gear sets may be disposed sequentially from an engine side. 
     The third clutch may be disposed between the fifth rotation shaft and the eighth rotation shaft. 
     A first forward speed stage may be achieved by operation of the first clutch and the first and second brakes, a second forward speed stage may be achieved by operation of the third clutch and the first and second brakes, a third forward speed stage may be achieved by operation of the first and third clutches and the second brake, a fourth forward speed stage may be achieved by operation of the third and fourth clutches and the second brake, a fifth forward speed stage may be achieved by operation of the first and fourth clutches and the second brake, a sixth forward speed stage may be achieved by operation of the first and second clutches and the second brake, a seventh forward speed stage may be achieved by operation of the first, second, and third clutches, an eighth forward speed stage may be achieved by operation of the first and second clutches and the first brake, a ninth forward speed stage may be achieved by operation of the second and fourth clutches and the first brake, and a reverse speed stage may be achieved by operation of the second clutch and the first and second brakes. 
     According to various aspects of the present invention, a planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting changed torque, a first planetary gear set including a first sun gear, a first planet carrier, and a first ring gear, a second planetary gear set including a second sun gear, a second planet carrier, and a second ring gear, a third planetary gear set including a third sun gear, a third planet carrier, and a third ring gear, a fourth planetary gear set including a fourth sun gear, a fourth planet carrier, and a fourth ring gear, a fifth planetary gear set including a fifth sun gear, a fifth planet carrier, and a fifth ring gear, a first rotation shaft including the first ring gear and selectively connected to a transmission housing, a second rotation shaft including the first planet carrier and the fifth ring gear, a third rotation shaft including the first and second sun gears and selectively connected to the transmission housing, a fourth rotation shaft including the second planet carrier and directly connected to the input shaft, a fifth rotation shaft including the second ring gear and the third and fourth sun gears, a sixth rotation shaft including the third and fourth planet carriers and selectively connected to the second rotation shaft, a seventh rotation shaft including the third ring gear and selectively connected to the fourth rotation shaft, an eighth rotation shaft including the fourth ring gear and the fifth sun gear and selectively connected to the fifth rotation shaft, a ninth rotation shaft including the fifth planet carrier, selectively connected to the fifth rotation shaft, and directly connected to the output shaft, and six friction elements disposed between one rotation shaft and another rotation shaft or between one rotation shaft and the transmission housing. 
     Each of the first, second, third, fourth, and fifth planetary gear sets may be a single pinion planetary gear set. 
     The six friction elements comprise a first clutch disposed between the fourth rotation shaft and the seventh rotation shaft, a second clutch disposed between the second rotation shaft and the sixth rotation shaft, a third clutch disposed between the fifth rotation shaft and the eighth rotation shaft, a fourth clutch disposed between the fifth rotation shaft and the ninth rotation shaft, a first brake disposed between the third rotation shaft and the transmission housing, and a second brake disposed between the first rotation shaft and the transmission housing. 
     Various embodiments of the present invention may achieve nine forward speed stages by combining five planetary gear sets that are simple planetary gear sets with six friction elements. Therefore, power delivery performance and fuel economy may be improved. 
     In addition, three friction elements operate at each speed stage, and as a result, a friction drag loss is decreased by minimizing the number of friction elements which do not operate. Therefore, drag torque and power loss may be reduced. 
     It is understood that the term “vehicle” or “vehicular” or other similar terms as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g., fuel derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example, both gasoline-powered and electric-powered vehicles. 
     The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an exemplary planetary gear train according to the present invention. 
         FIG. 2  is an operation chart of friction elements at each speed in the exemplary planetary gear train according to the present invention. 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
       FIG. 1  is a schematic diagram of a planetary gear train according to various embodiments of the present invention. 
     Referring to  FIG. 1 , a planetary gear train according to various embodiments of the present invention includes first, second, third, fourth, and fifth planetary gear sets PG 1 , PG 2 , PG 3 , PG 4 , and PG 5  disposed on the same axis, and input shaft IS, an output shaft OS, nine rotation shafts TM 1  to TM 9  including at least one of rotation elements of the first, second, third, fourth, and fifth planetary gear sets PG 1 , PG 2 , PG 3 , PG 4 , and PG 5 , six friction elements C 1  to C 4  and B 1  to B 2 , and a transmission housing H. 
     As a result, torque input from the input shaft IS is changed by cooperation of the first, second, third, fourth, and fifth planetary gear sets PG 1 , PG 2 , PG 3 , PG 4 , and PG 5 , and the changed torque is output through the output shaft OS. 
     The simple planetary gear sets are disposed in a sequence of the first, second, third, fourth, and fifth planetary gear sets PG 1 , PG 2 , PG 3 , PG 4 , and PG 5  from an engine side. 
     The input shaft IS is an input member and power from a crankshaft of an 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  of a first rotation element N 1 , a first planet carrier PC 1  of a second rotation element N 2  rotatably supporting a first pinion P 1  externally engaged with the first sun gear S 1 , and a first ring gear R 1  of a third rotation element N 3  internally engaged with the first pinion P 1 . 
     The second planetary gear set PG 2  is a single pinion planetary gear set, and includes a second sun gear S 2  of a fourth rotation element N 4 , a second planet carrier PC 2  of a fifth rotation element N 5  rotatably supporting a second pinion P 2  externally engaged with the second sun gear S 2 , and a second ring gear R 2  of a sixth rotation element N 6  internally engaged with the second pinion P 2 . 
     The third and fourth planetary gear sets PG 3  and PG 4  are single pinion planetary gear sets, and one rotation element of the third planetary gear set PG 3  is directly connected to one rotation element of the fourth planetary gear set PG 4  and another rotation element of the third planetary gear set PG 3  is directly connected to another rotation element of the fourth planetary gear set PG 4  such that the third and fourth planetary gear sets PG 3  and PG 4  operated as a compound planetary gear set CPG having four rotation elements. Herein, the compound planetary gear set CPG includes third and fourth sun gears S 3  and S 4  of a seventh rotation element N 7 , third and fourth planet carriers PC 3  and PC 4  of an eighth rotation element N 8  rotatably supporting third and fourth pinions P 3  and P 4  externally engaged with the third and fourth sun gears S 3  and S 4  respectively, and a fourth ring gear R 4  of a ninth rotation element N 9  internally engaged with the fourth pinion P 4 , and a third ring gear R 3  of a tenth rotation element N 10  internally engaged with the third pinion P 3 . 
     The fifth planetary gear set PG 5  is a single pinion planetary gear set, and includes a fifth sun gear S 5  of an eleventh rotation element N 11 , a fifth planet carrier PC 5  of a twelfth rotation element N 12  rotatably supporting a fifth pinion P 5  externally engaged with the fifth sun gear S 5 , and a fifth ring gear R 5  of a thirteenth rotation element N 13  internally engaged with the fifth pinion P 5 . 
     The first rotation element N 1  is directly connected to the fourth rotation element N 4 , the second rotation element N 2  is directly connected to the thirteenth rotation element, the sixth rotation element N 6  is directly connected to the seventh rotation element N 7 , and the tenth rotation element N 10  is directly connected to the eleventh rotation element N 11  such that the first, second, third, fourth, and fifth planetary gear sets PG 1 , PG 2 , PG 3 , PG 4 , and PG 5  have nine rotation shafts TM 1  to TM 9 . 
     The nine rotation shafts TM 1  to TM 9  will be described in further detail. 
     The first rotation shaft TM 1  includes the first ring gear R 1  of the third rotation element N 3  and is selectively connected to the transmission housing H so as to be operated as a selective fixed element. 
     The second rotation shaft TM 2  includes the first planet carrier PC 1  and the fifth ring gear R 5  that are the second and thirteenth rotation elements N 2  and N 13  respectively. 
     The third rotation shaft TM 3  includes the first and second sun gears S 1  and S 2  that are the first and fourth rotation elements N 1  and N 4  respectively, and is selectively connected to the transmission housing H so as to be operated as a selective fixed element. 
     The fourth rotation shaft TM 4  includes the second planet carrier PC 2  of the fifth rotation element N 5  and is directly connected to the input shaft IS so as to be continuously operated as an input element. 
     The fifth rotation shaft TM 5  includes the second ring gear R 2  and the third and fourth sun gears S 3  and S 4  that are the sixth rotation element N 6  and the seventh rotation element N 7  respectively. 
     The sixth rotation shaft TM 6  includes the third and fourth planet carriers PC 3  and PC 4  of the eighth rotation element N 8  and is selectively connected to the second rotation shaft TM 2 . 
     The seventh rotation shaft TM 7  includes the third ring gear R 3  of the ninth rotation element N 9  and is selectively connected to the fourth rotation shaft TM 4  so as to be operated as a selective input element. 
     The eighth rotation shaft TM 8  includes the fourth ring gear R 4  of the tenth rotation element N 10  and the fifth sun gear S 5  of the eleventh rotation element N 11 , and is selectively connected to the fifth rotation shaft TM 5 . 
     The ninth rotation shaft TM 9  includes the fifth planet carrier PC 5  of the twelfth rotation element N 12 , is selectively connected to the fifth rotation shaft TM 5 , and is directly connected to the output shaft OS so as to be continuously operated as an output element. 
     In addition, four clutches C 1 , C 2 , C 3 , and C 4  which are friction elements are disposed at connection portions between the input shaft IS and any one rotation shaft or between any two rotation shafts. 
     In addition, two brakes B 1  and B 2  which are friction elements are disposed at connection portions between any one rotation shaft and the transmission housing H. 
     The six friction elements C 1  to C 4  and B 1  to B 2  are described in further detail. 
     A first clutch C 1  is disposed between the fourth rotation shaft TM 4  and the seventh rotation shaft TM 7  and selectively connects the fourth rotation shaft TM 4  and the seventh rotation shaft TM 7 . 
     A second clutch C 2  is disposed between the second rotation shaft TM 2  and the sixth rotation shaft TM 6  and selectively connects the second rotation shaft TM 2  and the sixth rotation shaft TM 6 . 
     A third clutch C 3  is disposed between the fifth rotation shaft TM 5  and the eighth rotation shaft TM 8  and selectively connects the fifth rotation shaft TM 5  and the eighth rotation shaft TM 8  so as to cause the third planetary gear set PG 3  and the fourth planetary gear set PG 4  to become direct-coupling states. 
     A fourth clutch C 4  is disposed between the fifth rotation shaft TM 5  and the ninth rotation shaft TM 9  and selectively connects the fifth rotation shaft TM 5  and the ninth rotation shaft TM 9 . 
     A first brake B 1  is interposed between the third rotation shaft TM 3  and the transmission housing H and causes the third rotation shaft TM 3  to be operated as the selective fixed element. 
     A second brake B 2  is interposed between the first rotation shaft TM 1  and the transmission housing H and causes the first rotation shaft TM 1  to be operated as the selective fixed element. 
     The friction elements including 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 multi-plates friction elements of wet type that are operated by hydraulic pressure. 
       FIG. 2  is an operation chart of friction elements at each speed in the planetary gear train according to various embodiments of the present invention. 
     As shown in  FIG. 2 , three friction elements are operated at each speed stage in the planetary gear train according to various embodiments of the present invention. 
     The first clutch C 1  and the first and second brakes B 1  and B 2  are operated at a first forward speed stage 1ST. The fourth rotation shaft TM 4  and the seventh rotation shaft TM 7  due to operation of the first clutch C 1  are operated as the input elements, and the first, second, and third rotation shafts TM 1 , TM 2 , and TM 3  are operated as the fixed elements by operation of the first and second brakes B 1  and B 2 . Therefore, the first forward speed stage is achieved. 
     The third clutch C 3  and the first and second brakes B 1  and B 2  are operated at a second forward speed stage 2ND. In a state that the fifth rotation shaft TM 5  is connected to the eighth rotation shaft TM 8  by operation of the third clutch C 3 , the fourth rotation shaft TM 4  is operated as the input element, and the first, second, and third rotation shafts TM 1 , TM 2 , and TM 3  are operated as the fixed elements by operation of the first and second brakes B 1  and B 2 . Therefore, the second forward speed stage is achieved. 
     The first and third clutches C 1  and C 3  and the second brake B 2  are operated at a third forward speed stage 3RD. In a state that the fifth rotation shaft TM 5  is connected to the eighth rotation shaft TM 8  by operation of the third clutch C 3 , the fourth rotation shaft TM 4  and the seventh rotation shaft TM 7  due to operation of the first clutch C 1  are operated as the input elements, and the first rotation shaft TM 1  is operated as the fixed element by operation of the second brake B 2 . Therefore, the third forward speed stage is achieved. 
     The third and fourth clutches C 3  and C 4  and the second brake B 2  are operated at a fourth forward speed stage 4TH. In a state that the fifth rotation shaft TM 5  is connected to the eighth rotation shaft TM 8  by operation of the third clutch C 3  and the fifth rotation shaft TM 5  is connected to the ninth rotation shaft TM 9  by operation of the fourth clutch C 4 , the fourth rotation shaft TM 4  is operated as the input element and the first rotation shaft TM 1  is operated as the fixed element by operation of the second brake B 2 . Therefore, the fourth forward speed stage is achieved. 
     The first and fourth clutches C 1  and C 4  and the second brake B 2  are operated at a fifth forward speed stage 5TH. In a state that the fifth rotation shaft TM 5  is connected to the ninth rotation shaft TM 9  by operation of the fourth clutch C 4 , the fourth rotation shaft TM 4  and the seventh rotation shaft TM 7  are operated as the input elements by operation of the first clutch C 1 , the first rotation shaft TM 1  is operated as the fixed element by operation of the second brake B 2 . Therefore, the fifth forward speed stage is achieved. 
     The first and second clutches C 1  and C 2  and the second brake B 2  are operated at a sixth forward speed stage 6TH. In a state that the second rotation shaft TM 2  is connected to the sixth rotation shaft TM 6  by operation of the second clutch C 2 , the fourth rotation shaft TM 4  and the seventh rotation shaft TM 7  are operated as the input elements by operation of the first clutch C 1 , and the first rotation shaft TM 1  is operated as the fixed element by operation of the second brake B 2 . Therefore, the sixth forward speed stage is achieved. 
     The first, second, and third clutches C 1 , C 2 , and C 3  are operated at a seventh forward speed stage 7TH. In a state that the second rotation shaft TM 2  is connected to the sixth rotation shaft TM 6  by operation of the second clutch C 2  and the fifth rotation shaft TM 5  is connected to the eighth rotation shaft TM 8  by operation of the third clutch C 3 , the fourth rotation shaft TM 4  and the seventh rotation shaft TM 7  are operated as the input elements such that all the planetary gear sets become direct-coupling states. Therefore, the seventh forward speed stage is achieved. At the seventh forward speed stage, a rotation speed that is the same as that of the input shaft IS is output. 
     The first and second clutches C 1  and C 2  and the first brake B 1  are operated at an eighth forward speed stage 8TH. In a state that the second rotation shaft TM 2  is connected to the sixth rotation shaft TM 6  by operation of the second clutch C 2 , the fourth rotation shaft TM 4  and the seventh rotation shaft TM 7  are operated as the input elements by operation of the first clutch C 1  and the third rotation shaft TM 3  is operated as the fixed element by operation of the first brake B 1 . Therefore, the eighth forward speed stage is achieved. 
     The second and fourth clutches C 2  and C 4  and the first brake B 1  are operated at the ninth forward speed stage 9TH. In a state that the second rotation shaft TM 2  is connected to the sixth rotation shaft TM 6  by operation of the second clutch C 2  and the fifth rotation shaft TM 5  is connected to the ninth rotation shaft TM 9  by operation of the fourth clutch C 4 , the fourth rotation shaft TM 4  is operated as the input element and the third rotation shaft TM 3  is operated as the fixed element by operation of the first brake B 1 . Therefore, the ninth forward speed stage is achieved. 
     The second clutch C 2  and the first and second brakes B 1  and B 2  are operated at a reverse speed stage REV. In a state that the second rotation shaft TM 2  is connected to the sixth rotation shaft TM 6  by operation of the second clutch C 2 , the fourth rotation shaft TM 4  is operated as the input element and the first, second, and third rotation shafts TM 1 , TM 2 , and TM 3  are operated as the fixed elements by operation of the first and second brakes B 1  and B 2 . Therefore, the reverse speed stage is achieved. 
     The planetary gear train according to various embodiments of the present invention may achieve nine forward speed stages and one reverse speed stage by controlling five planetary gear sets PG 1 , PG 2 , PG 3 , PG 4 , and PG 5  through four clutches C 1 , C 2 , C 3 , and C 4  and two brakes B 1  and B 2 . 
     Therefore, the planetary gear train according to various embodiments of the present invention may improve power delivery efficiency and fuel economy due to multiple gear stages. 
     In addition, since three friction elements operate at each speed stage and the number of non-operating friction elements is minimized, a friction drag loss may be decreased. Therefore, power delivery efficiency and fuel economy may be improved. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.