Abstract:
A gear train of an automatic transmission for vehicles which achieving at least ten forward speeds and one reverse speed, may include an input shaft receiving torque of an engine which may be driving source, an output gear outputting a changed torque, first, second, third, and fourth planetary gear sets respectively having first, second, third, and fourth sun gears, first, second, third, and fourth planet carriers, and first, second, third, and fourth ring gears as rotation elements thereof, eight rotation shafts formed by connecting one rotation element to other rotation element, the input shaft, or the output gear, or being the rotation element, and friction members provided with first, second, third, and fourth clutches disposed between selected rotation shafts and controls delivery of the torque therebetween and first and second brakes selectively connecting selected rotation shaft to a transmission housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2010-0063167 filed in the Korean Intellectual Property Office on Jun. 30, 2010, the entire contents of which is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a gear train of an automatic transmission for vehicles which achieves at least ten forward speeds and one reverse speed by combining four simple planetary gear sets with four clutches and two brakes such that power delivery performance is improved and fuel consumption is reduced. 
     2. Description of Related Art 
     A typical shift mechanism of an automatic transmission utilizes a combination of a plurality of planetary gear sets. A gear train of such an automatic transmission that includes the plurality of planetary gear sets changes rotational speed and torque received from a torque converter of the automatic transmission, and accordingly transmits the changed torque to an output shaft. 
     It is well known that when a transmission realizes a greater number of shift speeds, speed ratios of the transmission can be more optimally designed, and therefore a vehicle can have economical fuel mileage and better performance. For that reason, an automatic transmission that is able to realize more shift speeds is under continuous investigation. 
     In addition, with the same number of speeds, features of a gear train, such as durability, efficiency in power transmission, and size, substantially depend on the layout of the combined planetary gear sets. Therefore, designs for a combining structure of a gear train are also under continuous investigation. 
     A manual transmission that has too many speeds causes inconvenience to a driver. Therefore, the advantageous features of having more shift-speeds are more important in an automatic transmission because an automatic transmission automatically controls the shifting operations. 
     Currently, four-speed and five-speed automatic transmissions are most often found on the market. However, six-speed automatic transmissions have also been realized for enhancement of performance of power transmission and for enhanced fuel mileage of a vehicle. In addition, seven-speed automatic transmissions and eight-speed automatic transmissions have been developed at a good pace. 
     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 OF THE INVENTION 
     Various aspects of the present invention are directed to provide a gear train of an automatic transmission for vehicles having advantages of simplifying structures of the automatic transmission and improving power delivery performance and fuel economy as a consequence of realizing at least ten forward speeds and one reverse speed by combining four simple planetary gear sets with four clutches and two brakes. 
     A gear train of an automatic transmission for vehicles according to exemplary embodiments of the present invention may achieve at least ten forward speeds and one reverse speed. The gear train may include an input shaft receiving torque of an engine which may be driving source, an output gear outputting changed torque, first, second, third, and fourth planetary gear sets respectively having first, second, third, and fourth sun gears, first, second, third, and fourth planet carriers, and first, second, third, and fourth ring gears as rotation elements thereof, eight rotation shafts formed by connecting one rotation element to other rotation element, the input shaft, or the output gear, or being the rotation element, and friction members provided with first, second, third, and fourth clutches disposed between selected rotation shafts and controls delivery of the torque therebetween and first and second brakes selectively connecting selected rotation shaft to a transmission housing. 
     The eight rotation shafts may include a first rotation shaft directly connecting the input shaft with the second planet carrier, a second rotation shaft directly connecting the output gear with the third planet carrier, a third rotation shaft directly connecting the first planet carrier with the second sun gear, a fourth rotation shaft being the first sun gear, a fifth rotation shaft directly connecting the third sun gear with the fourth ring gear, a sixth rotation shaft directly connecting the first ring gear with the third ring gear, a seventh rotation shaft directly connecting the second ring gear with the fourth sun gear, and an eighth rotation shaft being the fourth planet carrier. 
     The friction members may include the first clutch selectively connecting the second rotation shaft with the eighth rotation shaft, the second clutch selectively connecting the seventh rotation shaft with the eighth rotation shaft, the third clutch selectively connecting the first rotation shaft with the fifth rotation shaft, the fourth clutch selectively connecting the sixth rotation shaft with the eighth rotation shaft, the first brake selectively connecting the fourth rotation shaft with the transmission housing, and the second brake selectively connecting the third rotation shaft with the transmission housing. 
     According to the first exemplary embodiment, the first planetary gear set may be disposed close to the engine and the second, third, and fourth planetary gear sets may be sequentially disposed at the rear of the first planetary gear set. 
     The first and second brakes may be disposed at the front of the first planetary gear set, the first and fourth clutches may be disposed between the second and third planetary gear sets, and the second and third clutches may be disposed at the rear of the fourth planetary gear set. 
     The first planetary gear set may be a double pinion planetary gear set, and the second, third, and fourth planetary gear sets may be single pinion planetary gear sets. 
     The third clutch and the first and second brakes may be operated at a first forward speed, the second clutch and the first and second brakes may be operated at a second forward speed, the second and third clutches and the first brake may be operated at a third forward speed, the first and second clutches and the first brake may be operated at a fourth forward speed, the first and third clutches and the first brake may be operated at a fifth forward speed, the third and fourth clutches and the first brake may be operated at a sixth forward speed, the second, third, and fourth clutches may be operated at a seventh forward speed, the third and fourth clutches and the second brake may be operated at an eighth forward speed, the first and third clutches and the second brake may be operated at a ninth forward speed, the first and second clutches and the second brake may be operated at a tenth forward speed, and the first clutch and the first and second brakes may be operated at a reverse speed. 
     According to the second exemplary embodiment, the first planetary gear set may be disposed close to the engine and the third, fourth, and second planetary gear sets may be sequentially disposed at the rear of the first planetary gear set. 
     The first and second brakes may be disposed at the front of the first planetary gear set, the first and fourth clutches may be disposed between the first and third planetary gear sets, and the second and third clutches may be disposed between the fourth and second planetary gear sets. 
     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 of the Invention, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a gear train according to the first exemplary embodiment of the present invention. 
         FIG. 2  is an operational chart for a gear train according to the first exemplary embodiment of the present invention. 
         FIG. 3  is a lever diagram for a gear train according to the first exemplary embodiment of the present invention at the first forward speed. 
         FIG. 4  is a lever diagram for a gear train according to the first exemplary embodiment of the present invention at the second forward speed. 
         FIG. 5  is a lever diagram for a gear train according to the first exemplary embodiment of the present invention at the third forward speed. 
         FIG. 6  is a lever diagram for a gear train according to the first exemplary embodiment of the present invention at the fourth forward speed. 
         FIG. 7  is a lever diagram for a gear train according to the first exemplary embodiment of the present invention at the fifth forward speed. 
         FIG. 8  is a lever diagram for a gear train according to the first exemplary embodiment of the present invention at the sixth forward speed. 
         FIG. 9  is a lever diagram for a gear train according to the first exemplary embodiment of the present invention at the seventh forward speed. 
         FIG. 10  is a lever diagram for a gear train according to the first exemplary embodiment of the present invention at the eighth forward speed. 
         FIG. 11  is a lever diagram for a gear train according to the first exemplary embodiment of the present invention at the ninth forward speed. 
         FIG. 12  is a lever diagram for a gear train according to the first exemplary embodiment of the present invention at the tenth forward speed. 
         FIG. 13  is a lever diagram for a gear train according to the first exemplary embodiment of the present invention at the reverse speed. 
         FIG. 14  is a schematic diagram of a gear train according to the second exemplary embodiment of 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. 
     In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
     DETAILED DESCRIPTION OF THE INVENTION 
     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 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. 
     Description of components that are not necessary for explaining the present invention will be omitted, and the same constituent elements are denoted by the same reference numerals in this specification. 
     In the detailed description, ordinal numbers are used for distinguishing constituent elements having the same terms, and have no specific meanings. 
       FIG. 1  is a schematic diagram of a gear train according to the first exemplary embodiment of the present invention. A gear train according to the first exemplary embodiment of the present invention includes first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  disposed on the same axis, clutch means including four clutches C 1 , C 2 , C 3 , and C 4 , and brake means including two brakes B 1  and B 2 . 
     Accordingly, a rotational speed input from an input shaft IS is changed by the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  and is output through an output gear OG. The first planetary gear set PG 1  is disposed close to an engine, and the second, third, and fourth planetary gear sets PG 2 , PG 3 , and PG 4  are sequentially dispose at the rear of the first planetary gear set PG 1 . 
     The input shaft IS is an input member and denotes a turbine shaft of a torque converter. Torque transmitted from a crankshaft of the engine is converted by the torque converter and is input to the gear train through the input shaft IS. The output gear OG is an output member and is connected to a well-known differential apparatus so as to transmit an output of the gear train to driving wheels. 
     The first planetary gear set PG 1  is a double pinion planetary gear set, and has three rotation elements including a sun gear, a planet carrier, and a ring gear. For better comprehension and ease of description, the sun gear is indicated by a first sun gear S 1 , the planet carrier is indicated by a first planet carrier PC 1 , and the ring gear is indicated by a first ring gear R 1 . 
     The second planetary gear set PG 2  is a single pinion planetary gear set, and has three rotation elements including a sun gear, a planet carrier, and a ring gear. For better comprehension and ease of description, the sun gear is indicated by a second sun gear S 2 , the planet carrier is indicated by a second planet carrier PC 2 , and the ring gear is indicated by a second ring gear R 2 . 
     The third planetary gear set PG 3  is a single pinion planetary gear set, and has three rotation elements including a sun gear, a planet carrier, and a ring gear. For better comprehension and ease of description, the sun gear is indicated by a third sun gear S 3 , the planet carrier is indicated by a third planet carrier PC 3 , and the ring gear is indicated by a third ring gear R 3 . 
     The fourth planetary gear set PG 4  is a single pinion planetary gear set, and has three rotation elements including a sun gear, a planet carrier, and a ring gear. For better comprehension and ease of description, the sun gear is indicated by a fourth sun gear S 4 , the planet carrier is indicated by a fourth planet carrier PC 4 , and the ring gear is indicated by a fourth ring gear R 4 . 
     The rotation elements of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  are connected such that one rotation element of the first planetary gear set PG 1  is connected to one rotation element of the second planetary gear set PG 2 , another rotation element of the second planetary gear set PG 2  is connected to one rotation element of the fourth planetary gear set PG 4 , one rotation element of the third planetary gear set PG 3  is connected to another rotation element of the fourth planetary gear set PG 4 , and another rotation element of the third planetary gear set PG 3  is connected to another rotation element of the first planetary gear set PG 1 . Therefore, eight rotation shafts TM 1 -TM 8  are included. 
     In further detail, the first rotation shaft TM 1  directly connects the input shaft IS with the second planet carrier PC 2 . 
     The second rotation shaft TM 2  directly connects the output gear OG with the third planet carrier PC 3 . 
     The third rotation shaft TM 3  directly connects the first planet carrier PC 1  with the second sun gear S 2 . 
     The fourth rotation shaft TM 4  is the first sun gear S 1 . 
     The fifth rotation shaft TM 5  directly connects the third sun gear S 3  with the fourth ring gear R 4 . 
     The sixth rotation shaft TM 6  directly connects the first ring gear R 1  with the third ring gear R 3 . 
     The seventh rotation shaft TM 7  directly connects the second ring gear R 2  with the fourth sun gear S 4 . 
     The eighth rotation shaft TM 8  is the fourth planet carrier PC 4 . 
     A friction member C 1  is the first clutch, and selectively connects the second rotation shaft TM 2  with the eighth rotation shaft TM 8  so as to transmit torque therebetween. 
     A friction member C 2  is the second clutch, and selectively connects the seventh rotation shaft TM 7  with the eighth rotation shaft TM 8  so as to transmit torque therebetween. 
     A friction member C 3  is the third clutch, and selectively connects the first rotation shaft TM 1  with the fifth rotation shaft TM 5  so as to transmit torque therebetween. 
     A friction member C 4  is the fourth clutch, and selectively connects the sixth rotation shaft TM 6  with the eighth rotation shaft TM 8  so as to transmit torque therebetween. 
     A friction member B 1  is the first brake, and selectively connects the fourth rotation shaft TM 4  with a transmission housing H such that the fourth rotation shaft TM 4  is operated as a selective fixed element. 
     A friction member B 2  is the second brake, and selectively connects the third rotation shaft TM 3  with the transmission housing H such that the third rotation shaft TM 3  is operated as a selective fixed element. 
     Friction members 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  are conventional multi-plate friction elements of wet type that are operated by hydraulic pressure. 
     In addition, the first and second brakes B 1  and B 2  are disposed at an external circumferential portion of the front of the first planetary gear set PG 1 , the fourth and first clutches C 4  and C 1  are disposed between the second and third planetary gear sets PG 2  and PG 3 , and the second and third clutches C 2  and C 3  are disposed at the rear of the fourth planetary gear set PG 4 . 
     If the friction members are dispersed as described above, formation of hydraulic lines for supplying hydraulic pressure to such friction members may be simplified, and weight balance in the automatic transmission may be enhanced. 
       FIG. 2  is an operational chart for a gear train according to the first exemplary embodiment of the present invention. That is,  FIG. 2  shows which clutches and brakes are operated at each shift-speed. As shown in  FIG. 2 , three friction members are operated at each shift-speed according to the first exemplary embodiment of the present invention. 
     That is, the third clutch C 3  and the first and second brakes B 1  and B 2  are operated at a first forward speed D 1 , the second clutch C 2  and the first and second brakes B 1  and B 2  are operated at a second forward speed D 2 , the second and third clutches C 2  and C 3  and the first brake B 1  are operated at a third forward speed D 3 , the first and second clutches C 1  and C 2  and the first brake B 1  are operated at a fourth forward speed D 4 , the first and third clutches C 1  and C 3  and the first brake B 1  are operated at a fifth forward speed D 5 , the third and fourth clutches C 3  and C 4  and the first brake B 1  are operated at a sixth forward speed D 6 , the second, third, and fourth clutches C 2 , C 3 , and C 4  are operated at a seventh forward speed D 7 , the third and fourth clutches C 3  and C 4  and the second brake B 2  are operated at an eighth forward speed D 8 , the first and third clutches C 1  and C 3  and the second brake B 2  are operated at a ninth forward speed D 9 , the first and second clutches C 1  and C 2  and the second brake B 2  are operated at a tenth forward speed D 10 , and the first clutch C 1  and the first and second brakes B 1  and B 2  are operated at a reverse speed REV. 
       FIG. 3  to  FIG. 13  are lever diagrams for a gear train according to the first exemplary embodiment of the present invention. In the drawings, a lower horizontal line represents a rotational speed is “0”, and an upper horizontal line represents a rotational speed is “1.0”, that is, the rotational speed thereof is the same as that of the input shaft IS. 
     Three vertical lines of the first planetary gear set PG 1  sequentially represent a first rotation element N 1  to a third rotation element N 3  from the left to the right, and distances therebetween are set according to a gear ratio (teeth number of the sun gear/teeth number of the ring gear) of the first planetary gear set PG 1 . The first planet carrier PC 1  is set as the first rotation element N 1 , the first ring gear R 1  is set as the second rotation element N 2 , and the first sun gear S 1  is set as the third rotation element N 3 . 
     Three vertical lines of the second planetary gear set PG 2  sequentially represent a fourth rotation element N 4  to a sixth rotation element N 6  from the left to the right, and distances therebetween are set according to a gear ratio (teeth number of the sun gear/teeth number of the ring gear) of the second planetary gear set PG 2 . The second sun gear S 2  is set as the fourth rotation element N 4 , the second planet carrier PC 2  is set as the fifth rotation element N 5 , and the second ring gear R 2  is set as the sixth rotation element N 6 . 
     Three vertical lines of the fourth planetary gear set PG 4  sequentially represent a seventh rotation element N 7  to a ninth rotation element N 9  from the left to the right, and distances therebetween are set according to a gear ratio (teeth number of the sun gear/teeth number of the ring gear) of the fourth planetary gear set PG 4 . The fourth sun gear S 4  is set as the seventh rotation element N 7 , the fourth planet carrier PC 4  is set as the eighth rotation element N 8 , the fourth ring gear R 4  is set as the ninth rotation element N 9 . 
     Three vertical lines of the third planetary gear set PG 3  sequentially represent a tenth rotation element N 10  to a twelfth rotation element N 12  from the left to the right, and distances therebetween are set according to a gear ratio (teeth number of the sun gear/teeth number of the ring gear) of the third planetary gear set PG 3 . The third sun gear S 3  is set as the tenth rotation element N 10 , the third planet carrier PC 3  is set as the eleventh rotation element N 11 , the third ring gear R 3  is set as the twelfth rotation element N 12 . 
     [First Forward Speed] 
     As shown in  FIG. 2 , the third clutch C 3  and the first and second brakes B 1  and B 2  are operate at the first forward speed D 1 . 
     As shown in  FIG. 3 , in a state that a rotation speed of the input shaft IS is input to the fifth rotation element N 5 , all the rotation elements of the first planetary gear set PG 1  are stopped by operations of the first and second brakes B 1  and B 2  and the fourth rotation element N 4  directly connected to the first rotation element N 1  is operated as a fixed element. Accordingly, the sixth rotation element N 6  outputs an increased rotation speed. 
     In addition, the rotation speed of the input shaft IS is transmitted to the ninth rotation element N 9  and the tenth rotation element N 10  by operation of the third clutch C 3 , and the rotation speed of the sixth rotation element N 6  is transmitted to the seventh rotation element N 7  directly connected thereto. 
     At this state, the twelfth rotation element N 12  directly connected to the second rotation element N 2  is operated as the fixed element. Therefore, a first shift line SP 1  connecting the tenth rotation element N 10  and the twelfth rotation element N 12  is formed and the first forward speed D 1  is output through the eleventh rotation element N 11  that is the output member. 
     [Second Forward Speed] 
     As shown in  FIG. 2 , the third clutch C 3  that was operated at the first forward speed D 1  is released and the second clutch C 2  is operated at the second forward speed D 2 . 
     As shown in  FIG. 4 , the fourth rotation element N 4  is operated as the fixed element and the rotation speed of the input shaft IS is input to the fifth rotation element N 5 . Therefore, the sixth rotation element N 6  outputs an increased rotation speed and the increased rotation speed is transmitted to the seventh rotation element N 7 . 
     At this state, the fourth planetary gear set PG 4  becomes direct-coupling state by operation of the second clutch C 2 . The increased rotation speed is transmitted to the tenth rotation element N 10  directly connected to the ninth rotation element N 9 , and the twelfth rotation element N 12  directly connected to the second rotation element N 2  is operated as the fixed element. Therefore, a second shift line SP 2  connecting the tenth rotation element N 10  and the twelfth rotation element N 12  is formed and the second forward speed D 2  is output through the eleventh rotation element N 11  that is the output member. 
     [Third Forward Speed] 
     As shown in  FIG. 2 , the second brake B 2  that was operated at the second forward speed D 2  is released and the third clutch C 3  is operated at the third forward speed D 3 . 
     As shown in  FIG. 5 , the rotation speed of the input shaft IS is transmitted to the ninth rotation element N 9  and the tenth rotation element N 10  by operation of the third clutch C 3 . 
     At this time, the fourth planetary gear set PG 4  becomes direct-coupling state by operation of the second clutch C 2 . Since the fifth rotation element N 5  and the sixth rotation element N 6  are respectively connected to the seventh rotation element N 7  and the ninth rotation element N 9  of the fourth planetary gear set PG 4 , the second planetary gear set PG 2  also becomes direct-coupling state. 
     At this state, since torque of the fourth rotation element N 4  is transmitted to the first rotation element N 1  and the third rotation element N 3  is operated as the fixed element by operation of the first brake B 1 , the second rotation element N 2  outputs a reduced rotation speed. 
     In addition, in a state that the reduced rotation speed of the second rotation element N 2  is input to the twelfth rotation element N 12 , the rotation speed of the input shaft IS is input to the tenth rotation element N 10 . Therefore, a third shift line SP 3  connecting the tenth rotation element N 10  and the twelfth rotation element N 12  is formed and the third forward speed D 3  is output through the eleventh rotation element N 11  that is the output member. 
     [Fourth Forward Speed] 
     As shown in  FIG. 2 , the third clutch C 3  that was operated at the third forward speed D 3  is released and the first clutch C 1  is operated at the fourth forward speed D 4 . 
     As shown in  FIG. 6 , the fourth planetary gear set PG 4  becomes direct-coupling state by operation of the second clutch C 2 . In addition, since the eighth rotation element N 8  and the ninth rotation element N 9  are respectively connected to the eleventh rotation element N 11  and the tenth rotation element N 10  of the third planetary gear set PG 3  by operation of the first clutch C 1 , the third planetary gear set PG 3  also becomes direct-coupling state. 
     At this state, the rotation speed of the input shaft IS is input to the fifth rotation element N 5  and the third rotation element N 3  is operated at the fixed element by operation of the first brake B 1 . Therefore, the fourth rotation element N 4  and the first rotation element N 1  output an increased rotation speed and the second rotation element N 2  outputs a reduced rotation speed. 
     Since torque of the second rotation element N 2  is transmitted to the twelfth rotation element N 12  of the third planetary gear set PG 3  being the direct-coupling state, a fourth shift line SP 4  is formed and the fourth forward speed D 4  is output through the eleventh rotation element N 11 . 
     [Fifth Forward Speed] 
     As shown in  FIG. 3 , the second clutch C 2  that was operated at the fourth forward speed D 4  is released and the third clutch C 3  is operated at the fifth forward speed D 5 . 
     As shown in  FIG. 7 , in a state that the rotation speed of the input shaft IS is input to the fifth rotation element N 5 , the third rotation element N 3  is operated as the fixed element by operation of the first brake B 1 . In addition, the rotation speed of the input shaft IS is input to the ninth rotation element N 9  and tenth rotation element N 10  by operation of the third clutch C 3 . 
     At this state, the eleventh rotation element N 11  and the eighth rotation element N 8  rotate with the same rotation speed by operation of the first clutch C 1 . Therefore, a fifth shift line SP 5  connecting the tenth rotation element N 10  and the twelfth rotation element N 12  is formed by interaction of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  and the fifth forward speed D 5  is output through the eleventh rotation element N 11 . 
     [Sixth Forward Speed] 
     As shown in  FIG. 3 , the first clutch C 1  that was operated at the fifth forward speed D 5  is released and the fourth clutch C 4  is operated at the sixth forward speed D 6 . 
     As shown in  FIG. 8 , in a state that the rotation speed of the input shaft IS is input to the fifth rotation element N 5 , the third rotation element N 3  is operated as the fixed element by operation of the first brake B 1 . Therefore, the fourth rotation element N 4  and the first rotation element N 1  output an increased rotation speed and the second rotation element N 2  outputs a reduced rotation speed. 
     At this state, the rotation speed of the input shaft IS is transmitted to the ninth rotation element N 9  and the tenth rotation element N 10  by operation of the third clutch C 3 , and the reduced rotation speed of the second rotation element N 2  is transmitted to the eighth rotation element N 8  and the twelfth rotation element N 12  by operation of the fourth clutch C 4 . Therefore, a sixth shift line SP 6  connecting the tenth rotation element N 10  and the twelfth rotation element N 12  is formed and the sixth forward speed D 6  is output through the eleventh rotation element N 11 . 
     [Seventh Forward Speed] 
     As shown in  FIG. 2 , the first brake B 1  that was operated at the sixth forward speed D 6  is released and the second clutch C 2  is operated at the seventh forward speed D 7 . 
     As shown in  FIG. 9 , since three clutches C 2 , C 3 , and C 4  are operated and the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  become direct-coupling state. Therefore, a seventh shift line SP 7  is formed and the seventh forward speed D 7  is output through the eleventh rotation element N 11  that is the output member. The rotation speed of the seventh forward speed D 7  is the same as that of the input shaft IS. 
     [Eighth Forward Speed] 
     As shown in  FIG. 2 , the second clutch C 2  that was operated at the seventh forward speed D 7  is released and the second brake B 2  is operated at the eighth forward speed D 8 . 
     As shown in  FIG. 10 , in a state that the first rotation element N 1  and the fourth rotation element N 4  are operated as the fixed elements by operation of the second brake B 2 , the rotation speed of the input shaft IS is input to the fifth rotation element N 5 . Therefore, the second rotation element N 2  outputs an increased rotation speed and the increased rotation speed is transmitted to the twelfth rotation element N 12 . 
     In addition, the rotation speed of the input shaft IS is input to the tenth rotation element N 10  by operation of the third clutch C 3 . Therefore, an eighth shift line SP 8  connecting the tenth rotation element N 10  and the twelfth rotation element N 12  is formed and the eighth forward speed D 8  is output through the eleventh rotation element N 11  that is the output member. 
     [Ninth Forward Speed] 
     As shown in  FIG. 2 , the fourth clutch C 4  that was operated at the eighth forward speed D 8  is released and the first clutch C 1  is operated at the ninth forward speed D 9 . 
     As shown in  FIG. 11 , in a state that the first rotation element N 1  and the fourth rotation element N 4  are operated as the fixed elements by operation of the second brake B 2 , the rotation speed of the input shaft IS is input to the fifth rotation element N 5 . Therefore, the second rotation element N 2  outputs an increased rotation speed and the increased rotation speed is transmitted to the twelfth rotation element N 12 . 
     In addition, the rotation speed of the input shaft IS is input to the tenth rotation element N 10  by operation of the third clutch C 3 , and the eighth rotation element N 8  is connected to the eleventh rotation element N 11  by operation of the first clutch C 1 . Therefore, a ninth shift line SP 9  connecting the tenth rotation element N 10  and the twelfth rotation element N 12  is formed and the ninth forward speed D 9  is output through the eleventh rotation element N 11  that is the output member. 
     [Tenth Forward Speed] 
     As shown in  FIG. 2 , the third clutch C 3  that was operated at the ninth forward speed D 9  is released and the second clutch C 2  is operated at the tenth forward speed D 10 . 
     As shown in  FIG. 12 , the fourth planetary gear set PG 4  becomes direct-coupling state by operation of the second clutch C 2 , and the eighth rotation element N 8  and the ninth rotation element N 9  are respectively connected to the eleventh rotation element N 11  and the tenth rotation element N 10  of the third planetary gear set PG 3  by operation of the first clutch C 1 . Therefore, the third planetary gear set PG 3  also becomes direct-coupling state. 
     At this state, the rotation speed of the input shaft IS is input to the fifth rotation element N 5  and the first rotation element N 1  and the fourth rotation element N 4  are operated as the fixed elements by operation of the second brake B 2 . Therefore, the second rotation element N 2  outputs an increased rotation speed and the increased rotation speed is transmitted to the twelfth rotation element N 12 . 
     Accordingly, a tenth shift line SP 10  is formed and the tenth forward speed D 10  is output through the eleventh rotation element N 11  that is the output member. 
     [Reverse Speed] 
     As shown in  FIG. 2 , the first clutch C 1  and the first and second brakes B 1  and B 2  are operated at a reverse speed REV. 
     As shown in  FIG. 13 , in a state that the rotation speed of the input shaft IS is input to the fifth rotation element N 5 , all the rotation elements of the first planetary gear set PG 1  are stopped by operations of the first and second brakes B 1  and B 2 . Therefore, the fourth rotation element N 4  directly connected to the first planet carrier PC 1  of the first rotation element N 1  is operated as the fixed element. 
     Accordingly, an increased rotation speed of the sixth rotation element N 6  is input to the seventh rotation element N 7  and the twelfth rotation element N 12  directly connected to the second rotation element N 2  is operated as the fixed element. Therefore, a reverse shift line SR is formed and the reverse speed REV is output through the eleventh rotation element N 11  that is the output member. 
       FIG. 14  is a schematic diagram of a gear train according to the second exemplary embodiment of the present invention. Structures of the first, second, third, and fourth planetary gear sets PG 1 -PG 4  according to the second exemplary embodiment are the same as those according to the first exemplary embodiment. However, positions of the first, second, third, and fourth planetary gear sets PG 1 -PG 4  are changed. 
     That is, the first, second, third, and fourth planetary gear sets PG 1 -PG 4  are sequentially disposed from the engine according to the first exemplary embodiment, but the first, third, fourth, and second planetary gear sets PG 1 , PG 3 , PG 4 , and PG 2  are sequentially disposed from the engine according to the second exemplary embodiment. 
     Operations of the second exemplary embodiment is the same as those of the first exemplary embodiment, and detailed description thereof will be omitted. 
     As described above, ten forward speeds and one reverse speed are achieved by combining four simple planetary gear sets with four clutches and two brakes. Three friction elements are operated at each shift-speed. Therefore, power delivery performance and fuel economy may be improved. 
     Since the frictional members are dispersedly disposed, formation of hydraulic lines may be simplified, weight balance in an automatic transmission may be enhanced. 
     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.