Gear train of automatic transmission for vehicles

This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0041990 filed in the Korean Intellectual Property Office on May 6, 2008, the entire contents of which are incorporated herein for all purposes by this reference.

1. Field of the Invention

The present invention relates to a gear train of an automatic transmission for vehicles which provides at least eight forward speeds by combining four planetary gear sets with three clutches and three brakes.

2. Description of the 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 rotation 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 above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

The present invention has been made in an effort to provide a gear train of an automatic transmission for vehicles having advantages of improving power delivery performance and reducing fuel consumption as a consequence of realizing more than eight forward speeds by combining four planetary gear sets with three clutches and three brakes.

A gear train of an automatic transmission for vehicles according to an exemplary embodiment of the present invention may include: a first planetary gear set being a first simple planetary gear set having three rotation elements, and forming a first input pathway that receives a rotation speed input from an input shaft and outputs an increased rotation speed; a second planetary gear set formed by combining second, third, and fourth simple planetary gear sets such that one rotation element of the second simple planetary gear set is connected to one rotation element of the third simple planetary gear set, another rotation element of the third simple planetary gear set is connected to one rotation element of the fourth simple planetary gear set, and another rotation element of the fourth simple planetary gear set is connected to another rotation element of the second simple planetary gear set to have six rotation elements, and outputting a target rotation speed by using the reduced rotation speed selectively input from the first planetary gear set and the rotation speed of the input shaft input through a second input pathway and first and second variable input pathways; and a plurality of friction members including first, second, and third clutches that are disposed on the first and second variable input pathways and first, second, and third brakes that selectively connect some rotation elements of the first and second planetary gear sets to a transmission housing.

The first planetary gear set may be a single pinion planetary gear set having a first sun gear, a first ring gear, and a first planet carrier as rotation elements thereof, wherein the first sun gear directly connected to the transmission housing is operated as a first rotation element, the first planet carrier forming an intermediate output pathway is operated as a second rotation element, and the first ring gear forming the first input pathway that is directly connected to the input shaft is operated as a third rotation element.

The second planetary gear set may include the second simple planetary gear set that is a single pinion planetary gear set and has a second sun gear, a second ring gear, and a second planet carrier as rotation elements thereof, the third simple planetary gear set that is a single pinion planetary gear set and has a third sun gear, a third ring gear, and a third planet carrier as rotation elements thereof, and the fourth simple planetary gear set that is a double pinion planetary gear set and has a fourth sun gear, a fourth ring gear, and a fourth planet carrier as rotation elements thereof, wherein the second planet carrier is connected to the third ring gear, the third planet carrier is connected to the fourth planet carrier, and the fourth ring gear is connected to the second ring gear such that the third sun gear is operated as a fourth rotation element, the second sun gear is operated as a fifth rotation element, the third and fourth planet carriers are operated as a sixth rotation element, the second planet carrier and the third ring gear are operated as a seventh rotation element, the second ring gear and the fourth ring gear are operated as an eighth rotation element, and the fourth sun gear is operated as a ninth rotation element, and wherein the fourth rotation element is selectively connected to the input shaft and the second rotation element through the first variable input pathway and is selectively connected to the transmission housing, the fifth rotation element is selectively connected to the transmission housing, the sixth rotation element is selectively connected to the transmission housing and is selectively connected to the input shaft through the second variable input pathway, the seventh rotation element is connected to an output gear through an output pathway, the eighth rotation element is operated as an idle element, and the ninth rotation element is directly connected to the input shaft through the second input pathway.

The friction members may include: the first clutch disposed between the input shaft and the fourth rotation element; the second clutch disposed between the input shaft and the sixth rotation element; the third clutch disposed between the second rotation element and the fourth rotation element; the first brake disposed between the transmission housing and the fifth rotation element; the second brake disposed between the transmission housing and the sixth rotation element; and the third brake disposed between the transmission housing and the fourth rotation element.

The second brake B 2 may be disposed in parallel with a one-way clutch.

According to another exemplary embodiment of the present invention, the first planetary gear set may be a double pinion planetary gear set having a first sun gear, a first ring gear, and a first planet carrier as rotation elements thereof, wherein the first sun gear directly connected to the transmission housing is operated as a first rotation element, the first ring gear forming an intermediate output pathway is operated as a second rotation element, and the first planet carrier forming the first input pathway that is directly connected to the input shaft is operated as a third rotation element.

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 exemplary embodiments of the present invention.

FIG. 3 is a lever diagram at a first forward speed.

FIG. 4 is a lever diagram at a second forward speed.

FIG. 5 is a lever diagram at a third forward speed.

FIG. 6 is a lever diagram at a fourth forward speed.

FIG. 7 is a lever diagram at a fifth forward speed.

FIG. 8 is a lever diagram at a sixth forward speed.

FIG. 9 is a lever diagram at a seventh forward speed.

FIG. 10 is a lever diagram at an eighth forward speed.

FIG. 11 is a lever diagram at a first reverse speed.

FIG. 12 is a lever diagram at a second reverse speed.

FIG. 13 is a schematic diagram of a gear train according to the second exemplary embodiment of the present 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.

FIG. 1 shows a gear train according to the first exemplary embodiment of the present invention. The gear train includes first, second, third, and fourth simple planetary gear sets SPG 1 , SPG 2 , SPG 3 , and SPG 4 disposed on the same axis, clutch means consisting of three clutches C 1 , C 2 , and C 3 , and brake means consisting of three brakes B 1 , B 2 , and B 3 .

The first, second, third, and fourth simple planetary gear sets SPG 1 , SPG 2 , SPG 3 , and SPG 4 are sequentially disposed on an input shaft IS from an engine. A first planetary gear set PG 1 including the first simple planetary gear set SPG 1 reduces a rotation speed input from the input shaft IS and outputs a reduced rotation speed. A second planetary gear set PG 2 including the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 changes the reduced rotation speed selectively input from the first planetary gear set PG 1 and the rotation speed of the input shaft IS input through one input pathway IP 2 and two variable input pathways VIP 1 and VIP 2 into eight forward speeds and two reverse speeds and outputs the same through an output pathway OP.

The input shaft IS is an input member and represents a turbine shaft of a torque converter. Therefore, torque transmitted from a crankshaft of the engine to the torque converter is converted and then input to the gear train through the turbine shaft. A rotation speed changed in the gear train is transmitted to a well-known differential apparatus through an output gear OG of an output member.

The first simple planetary gear set SPG 1 is a single pinion planetary gear set, and the first simple planetary gear set SPG 1 includes a first sun gear S 1 , a first planet carrier PC 1 supporting a plurality of pinions engaged with the first sun gear S 1 , and a first ring gear R 1 engaged with the pinions as rotation elements thereof.

The second simple planetary gear set SPG 2 is a single pinion planetary gear set, and includes a second sun gear S 2 , a second planet carrier PC 2 supporting a plurality of pinions engaged with the second sun gear S 2 , and a second ring gear R 2 engaged with the pinions as rotation elements thereof.

The third simple planetary gear set SPG 3 is a single pinion planetary gear set, and includes a third sun gear S 3 , a third planet carrier PC 3 supporting a plurality of pinions engaged with the third sun gear S 3 , and a third ring gear R 3 engaged with the pinions as rotation elements thereof.

The fourth simple planetary gear set SPG 4 is a double pinion planetary gear set, and includes a fourth sun gear S 4 , a fourth planet carrier PC 4 supporting a plurality of pinions engaged with the fourth sun gear S 4 , and a fourth ring gear R 4 engaged with the pinions as rotation elements thereof.

The first planetary gear set PG 1 including the first simple planetary gear set SPG 1 outputs the reduced rotation speed. For this purpose, the first sun gear S 1 of a first rotation element N 1 is directly connected to the transmission housing H and is always operated as a fixed element, the first planet carrier PC 1 of a second rotation element N 2 forms an intermediate output pathway MOP that reduces a rotation speed input to the first ring gear R 1 and outputs a reduced rotation speed, and the first ring gear R 1 of a third rotation element N 3 forms a first input pathway IP 1 that is directly connected to the input shaft IS.

The second planetary gear set PG 2 consisting of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 is combined such that the second planet carrier PC 2 is connected to the third ring gear R 3 through a first power transmitting member TS 1 , the third planet carrier PC 3 is connected to the fourth planet carrier PC 3 through a second power transmitting member TS 2 , the fourth ring gear R 4 is connected to the second ring gear R 2 through a third power transmitting member TS 3 to have six rotation elements.

That is, the six rotation elements include the third sun gear S 3 of a fourth rotation element N 4 , the second sun gear S 2 of a fifth rotation element N 5 , the third and fourth planet carriers PC 3 and PC 4 of a sixth rotation element N 6 , the second planet carrier PC 2 and the third ring gear R 3 of a seventh rotation element N 7 , the second ring gear R 2 and the fourth ring gear R 4 of an eighth rotation element N 8 , and the fourth sun gear S 4 of a ninth rotation element N 9 .

The third sun gear S 3 of the fourth rotation element N 4 is selectively connected to the input shaft IS by interposing the first clutch Cl therebetween and is selectively connected to the first planet carrier PC 1 of the second rotation element N 2 by interposing the third clutch C 3 therebetween. The third and fourth planet carriers PC 3 and PC 4 of the sixth rotation element N 6 are selectively connected to the input shaft IS by interposing the second clutch C 2 therebetween.

The second sun gear S 2 of the fifth rotation element N 5 is selectively connected to the transmission housing H by interposing the first brake B 1 therebetween, and the second and third planet carriers PC 2 and PC 3 of the sixth rotation element N 6 are selectively connected to the transmission housing H by interposing therebetween a one-way clutch F and the second brake B 2 disposed in parallel with each other, and the third sun gear S 3 of the fourth rotation element N 4 is selectively connected to the transmission housing H by interposing the third brake B 3 therebetween.

Accordingly, the fourth rotation element N 4 forms the first variable input pathway VIP 1 where the rotation speed of the input shaft IS and the reduced rotation speed of the first planetary gear set PG 1 are input and is operated as a selective fixed member.

In addition, the fifth rotation element N 5 is operated as a selective fixed member, the sixth rotation element N 6 forms the second variable input pathway VIP 2 and is operated as a selectively fixed member, the seventh rotation element N 7 is connected to an output gear OG so as to form a final output pathway OP, the eighth rotation element N 8 is operated as an idle element, and the ninth rotation element N 9 forms the second input pathway IP 2 where the rotation speed of the input shaft IS is always input.

In addition, the third clutch C 3 is disposed at a front portion of the first simple planetary gear set SPG 1 , the first and third brakes B 1 and B 3 are disposed at an exterior circumferential portion of the first simple planetary gear set SPG 1 , the first clutch C 1 is disposed between the first and second simple planetary gear sets SPG 1 and SPG 2 , the one-way clutch F and the second brake B 2 are disposed at an exterior circumferential portion of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 , and the second clutch C 2 is disposed at a rear portion of the fourth simple planetary gear set SPG 4 .

If the friction elements are dispersed as described above, formation of hydraulic lines for supplying hydraulic pressure to such friction elements may be simplified, and weight balance in the automatic transmission may be enhanced.

The friction members consisting of the first, second, and third clutches C 1 , C 2 , and C 3 and the first, second, and third brakes B 1 , B 2 , and B 3 are conventional multi-plate friction members of wet type that are operated by hydraulic pressure. The friction members are connected to a hydraulic pressure control apparatus and are operated or released by a control of a transmission control unit (not shown) according to a driving condition.

FIG. 2 is an operational chart that shows friction elements (clutches and brakes) operated at each shift speed for exemplary embodiments of the present invention, and ● means an operation of the friction members. According to exemplary embodiments of the present invention, three friction members are operated so as to achieve shifting at each shift speed.

That is, the first brake B 1 and the one-way clutch F are operated at a first forward speed, the second and third brakes B 2 and B 3 are operated at a second forward speed, the third clutch C 3 and the first brake B 1 are operated at a third forward speed, the first clutch C 1 and the first brake B 1 are operated at a fourth forward speed, the second clutch C 2 and the first brake B 1 are operated at a fifth forward speed, the first and second clutches C 1 and C 2 are operated at a sixth forward speed, the second and third clutches C 2 and C 3 are operated at a seventh forward speed, the second clutch C 2 and the third brake B 3 are operated at an eighth forward speed, the third clutch C 3 and the second brake B 2 are operated at a first reverse speed, and the first clutch C 1 and the second brake B 2 are operated at a second reverse speed.

FIG. 3 to FIG. 11 show shift processes according to exemplary embodiments of the present invention. In the drawings, a lower horizontal line represents a rotation speed is “0”, and an upper horizontal line represents a rotation speed is “1.0”, that is, the rotation speed thereof is the same as that of the input shaft IS.

Three vertical lines of the first planetary gear set PG 1 including the first simple planetary gear set SPG 1 in the drawings represent the first sun gear S 1 of the first rotation element N 1 , the first planet carrier PC 1 of the second rotation element N 2 , and the first ring gear R 1 of the third rotation element N 3 sequentially from the left, and distances therebetween are set according to gear ratio of the first simple planetary gear set SPG 1 (teeth number of the sun gear/teeth number of the ring gear).

Six vertical lines of the second planetary gear set PG 2 including the second, third, and fourth simple planetary gear sets PG 2 , PG 3 , and PG 4 in the drawings represent the third sun gear S 3 of the fourth rotation element N 4 , the second sun gear S 2 of the fifth rotation element N 5 , the third and fourth planet carriers PC 3 and PC 4 of the sixth rotation element N 6 , the second planet carrier PC 2 and the third ring gear R 3 of the seventh rotation element N 7 , the second ring gear R 2 and the fourth ring gear R 4 of the eighth rotation element N 8 , and the fourth sun gear S 4 of the ninth rotation element N 9 sequentially from the left, and distances therebetween are set according to each gear ratio of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 (teeth number of the sun gear/teeth number of the ring gear).

Position of each rotation element in the lever diagram is well known to a person of an ordinary skill in the art who designs a gear train, and thus detailed description will be omitted.

The First Forward Speed

In the first forward speed, as shown in FIG. 2 , the first brake B 1 and the one-way clutch (F) are operated.

Then, as shown in FIG. 3 , in the first planetary gear set PG 1 receives torque from the input shaft IS, however, the first planetary gear set PG 1 does not participate in the shifting.

The ninth rotation element N 9 receives the torque from the input shaft IS through the second input pathway IP 2 and the fifth rotation element N 5 and the sixth rotation element N 6 are operated as fixed elements by operations of the first brake B 1 and the one-way clutch (F). Therefore, speed lines of the first forward speed are formed as a result of cooperation of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 and the seventh rotation element N 7 outputs the first forward speed D 1 . Herein, exemplary speed ratio is 4.45.

The Second Forward Speed

In the state of the first forward speed D 1 , as shown in FIG. 2 , the third brake B 3 is operated and the one-way clutch (F) is released to achieve the second forward speed D 2 .

Then, as shown in FIG. 4 , in the first planetary gear set PG 1 receives the torque from the input shaft IS, however, the first planetary gear set PG 1 does not participate in the shifting.

Then, the ninth rotation element N 9 receives the torque from the input shaft IS through the second input pathway IP 2 , and the fourth rotation element N 4 and the fifth rotation element N 5 are operated as fixed elements by operations of the first brake B 1 and the third brake B 3 . Therefore, speed lines of the second forward speed are formed as a result of cooperation of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 and the seventh rotation element N 7 outputs the second forward speed D 2 . Herein, exemplary speed ratio is 2.70.

The Third Forward Speed

In the state of the second forward speed D 2 , as shown in FIG. 2 , the third brake B 3 is released and the third clutch C 3 is operated to achieve the third forward speed D 3 .

Then, as shown in FIG. 5 , the ninth rotation element N 9 receives the torque from the input shaft IS through the second input pathway IP 2 , reduced rotational speed of the second rotation element N 2 outputting from the intermediate output pathway (MOP) by an operation of the third clutch C 3 is transmitted to the fourth rotation element N 4 via the first variable input pathway VIP 1 and the fifth rotation element N 5 is operated as a fixed element by an operation of the first brake B 1 .

Therefore, speed lines of the third forward speed are formed as a result of cooperation of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 and the seventh rotation element N 7 outputs the third forward speed D 3 . Herein, exemplary speed ratio is 2.03.

The Fourth Forward Speed

In the state of the third forward speed D 3 , as shown in FIG. 2 , the third clutch C 3 is released and the first clutch C 1 is operated to achieve the fourth forward speed D 4 .

Then, as shown in FIG. 6 , the ninth rotation element N 9 receives the torque from the input shaft IS through the second input pathway IP 2 , the torque from the input shaft IS is transmitted to the fourth rotation element N 4 via the first variable input pathway VIP 1 by an operation of the first clutch C 1 and the fifth rotation element N 5 is operated as a fixed element by an operation of the first brake B 1 .

Therefore, speed lines of the fourth forward speed are formed as a result of cooperation of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 and the seventh rotation element N 7 outputs the fourth forward speed D 4 . Herein, exemplary speed ratio is 1.68.

The Fifth Forward Speed

In the state of the fourth forward speed D 4 , as shown in FIG. 2 , first clutch C 1 is released and the second clutch C 2 is operated to achieve the fifth forward speed D 5 .

Then, as shown in FIG. 7 , the ninth rotation element N 9 receives the torque from the input shaft IS through the second input pathway IP 2 , the sixth rotation element N 6 receives the torque from the input shaft IS through the second variable input pathway VIP 2 by an operation of the second clutch C 2 and the fifth rotation element N 5 is operated as a fixed element by an operation of the first brake B 1 .

Therefore, speed lines of the fifth forward speed are formed as a result of cooperation of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 and the seventh rotation element N 7 outputs the fifth forward speed D 5 . Herein, exemplary speed ratio is 1.33.

The Sixth Forward Speed

In the state of the fifth forward speed D 5 , as shown in FIG. 2 , the first brake B 1 is released and the first clutch C 1 is operated to achieve the sixth forward speed D 6 .

Then, as shown in FIG. 8 , the ninth rotation element N 9 receives the torque from the input shaft IS through the second input pathway IP 2 and the torque from the input shaft IS is transmitted to the fourth rotation element N 4 and the sixth rotation element N 6 via the first and second variable input pathway VIP 1 and VIP 2 by operations of the first and second clutch C 1 and C 2 .

Therefore, the second, third, and fourth simple planetary gear set SPG 2 , SPG 3 , and SPG 4 rotates at the speed of the input shaft IS and the seventh rotation element N 7 outputs the sixth forward speed D 6 . Herein, exemplary speed ratio is 1.00.

The Seventh Forward Speed

In the state of the sixth forward speed D 6 , as shown in FIG. 2 , the first clutch C 1 is released and the third clutch C 3 is operated to achieve the seventh forward speed D 7 .

Then, as shown in FIG. 9 , the ninth rotation element N 9 receives the torque from the input shaft IS through the second input pathway IP 2 , the sixth rotation element N 6 receives the torque from the input shaft IS through the second variable input pathway VIP 2 by an operation of the second clutch C 2 and the reduced rotational speed of the second rotation element N 2 outputting from the intermediate output pathway (MOP) by an operation of the third clutch C 3 is transmitted to the fourth rotation element N 4 via the first variable input pathway VIP 1 .

Therefore, speed lines of the seventh forward speed are formed as a result of cooperation of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 and the seventh rotation element N 7 outputs the seventh forward speed D 7 . Herein, exemplary speed ratio is 0.86.

The Eighth Forward Speed

In the state of the seventh forward speed D 7 , as shown in FIG. 2 , the third clutch C 3 is released and the third brake B 3 is operated to achieve the eighth forward speed D 8 .

Then, as shown in FIG. 9 , the ninth rotation element N 9 receives the torque from the input shaft IS through the second input pathway IP 2 , the sixth rotation element N 6 receives the torque from the input shaft IS through the second variable input pathway VIP 2 by an operation of the second clutch C 2 and the fourth rotation element N 4 is operated as a fixed element by an operation of the third brake B 3 .

Therefore, speed lines of the eighth forward speed are formed as a result of cooperation of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 and the seventh rotation element N 7 outputs the eighth forward speed D 8 . Herein, exemplary speed ratio is 0.74.

The First Reverse Speed

In the first reverse speed, as shown in FIG. 2 , the third clutch C 3 and the second brake B 2 are operated.

Then, as shown in FIG. 11 , the ninth rotation element N 9 receives the torque from the input shaft IS through the second input pathway IP 2 , reduced rotational speed of the second rotation element N 2 outputting from the intermediate output pathway (MOP) by an operation of the third clutch C 3 is transmitted to the fourth rotation element N 4 via the first variable input pathway VIP 1 and the sixth rotation element N 6 is operated as a fixed element by an operation of the second brake B 2 .

Therefore, speed lines of the first reverse speed are formed as a result of cooperation of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 and the seventh rotation element N 7 outputs the first reverse speed RS 1 . Herein, exemplary speed ratio is −5.33.

The Second Reverse Speed

In the state of the first reverse speed RS 1 , as shown in FIG. 2 , the third clutch C 3 is released and the first clutch C 1 is operated to achieve the second reverse speed RS 2 .

Then, as shown in FIG. 12 , the ninth rotation element N 9 receives the torque from the input shaft IS through the second input pathway IP 2 , the fourth rotation element N 4 receives the torque from the input shaft IS via the first variable input pathway VIP 1 by an operation of the first clutch C 1 and the sixth rotation element N 6 is operated as a fixed element by an operation of the second brake B 2 .

Therefore, speed lines of the second reverse speed are formed as a result of cooperation of the second, third, and fourth simple planetary gear sets SPG 2 , SPG 3 , and SPG 4 and the seventh rotation element N 7 outputs the second reverse speed RS 2 . Herein, exemplary speed ratio is −2.91.

FIG. 13 shows a gear train according to the second exemplary embodiment of the present invention. The second planetary gear set PG 2 of the second exemplary embodiment is the same as that of the first exemplary embodiment, but the first planetary gear set PG 1 is a double pinion planetary gear set.

Accordingly, the first planet carrier PC 1 is changed from the second rotation element N 2 to the third rotation element N 3 and the first ring gear R 1 is changed from the third rotation element N 3 to the second rotation element N 2 .

The second and third rotation elements N 2 and N 3 are changed to each other according to the second exemplary embodiment but operations and shifting processes of the second exemplary embodiment is the same as those of the first exemplary embodiment. Therefore, detailed description will be omitted.

Since exemplary embodiments of the present invention realize eight forward speeds and two reverse speeds by combining four planetary gear sets with three clutches, three brakes, and one one-way clutch, power delivery performance may be improved and fuel consumption may be reduced.

Since the plurality of friction members are dispersed, formation of hydraulic lines may be simplified.

For convenience in explanation and accurate definition in the appended claims, the terms “upper” or “lower”, “front” or “rear”, and etc. are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures.

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.