Planetary gear train of automatic transmission for vehicles

The present application claims priority to Korean Patent Application No. 10-2012-0116826 filed on Oct. 19, 2012, the entire contents of which is incorporated herein for all purposes by this reference.

1. 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 that can improve mountability by reducing a length thereof and reduce fuel consumption by improving power delivery performance.

2. Description of Related Art

Typically, a planetary gear train is realized by combining a plurality of planetary gear sets and friction members. It is well known that when a planetary gear train realizes a greater number of shift speeds, speed ratios of the planetary gear train can be more optimally designed, and therefore a vehicle can have economical fuel mileage and better performance. For that reason, the planetary gear train that is able to realize more shift speeds is under continuous investigation.

Though achieving the same number of speeds, the planetary gear train has a different operating mechanism according to a connection between rotation elements (i.e., sun gear, planet carrier, and ring gear). In addition, the planetary gear train has different features such a durability, power delivery efficiency, and size depend on the layout thereof. Therefore, designs for a combining structure of a gear train are also under continuous investigation.

In addition, the planetary gear train realizes a plurality of shift-speeds. However, another friction member must be operated after one friction member is released so as to shift to a neighboring shift-speed from a view of shift control. In addition, a step ratio between the neighboring shift-speeds should be controlled to be suitable according to the planetary gear train.

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.

Various aspects of the present invention are directed to providing a planetary gear train of an automatic transmission for a vehicle having advantages of improving mountability by shortening a length thereof and reducing fuel consumption by improving power delivery performance as a consequence of achieving eight forward speeds and one reverse speed having excellent operating condition of frictional elements and step ratios by combining three planetary gear sets separately disposed on a first shaft and a second shaft, three externally-meshing gears, and five frictional elements.

In an aspect of the present invention, a planetary gear train of an automatic transmission for a vehicle, may include a first shaft receiving torque of an engine, a second shaft disposed in parallel with the first shaft and selectively receiving a rotation speed of the first shaft as an inverse rotation speed, a first planetary gear set disposed on the first shaft, and including a first ring gear directly connected to the first shaft so as to be continuously operated as an input element, a first planet carrier selectively operated as an output element, and a first sun gear selectively operated as an output element as rotation elements thereof, a second planetary gear set disposed on the second shaft, and including a second sun gear receiving an inverse rotation speed from the first planet carrier, a second ring gear selectively connected to the second shaft, and a second planet carrier as rotation elements thereof, a third planetary gear set disposed on the second shaft, and including a third sun gear directly connected to the second shaft, a third ring gear selectively connected to the first sun gear and receiving an inverse rotation speed, and a third planet carrier directly connected to the second planet carrier and directly connected to an output gear as rotation elements thereof, three transfer gears interposed at connecting portions between the rotation elements, and five frictional elements selectively interconnecting the rotation elements or selectively connecting the rotation elements to a transmission housing.

The first planetary gear set is a double pinion planetary gear set, the second planetary gear set is a single pinion planetary gear set, and the third planetary gear set is a single pinion planetary gear set.

The three transfer gears may include a first transfer gear including a first transfer drive gear selectively connected to the first shaft or the first planet carrier, and a first transfer driven gear connected to the second shaft, a second transfer gear including a second transfer drive gear connected to the first planet carrier and a second transfer driven gear connected to the second sun gear, and a third transfer gear including a third transfer drive gear selectively connected to the first sun gear and a third transfer driven gear connected to the third ring gear.

The first transfer driven gear is selectively connected to the second planet carrier.

The five frictional elements may include a first clutch mounted between the first sun gear and the third transfer gear, a second clutch mounted between the first shaft and the first transfer gear, a third clutch mounted between the second ring gear and the second shaft, a fourth clutch mounted between the first planet carrier and the first transfer gear, and a first brake mounted between the first sun gear and the transmission housing.

The second clutch is mounted between the first ring gear and the first transfer gear.

The third clutch is mounted between the second ring gear and the first transfer gear.

The fourth clutch is mounted between the first transfer gear and the second transfer gear.

The first clutch is mounted between the first sun gear and the third transfer drive gear, wherein the second clutch is mounted between the first shaft and the first transfer drive gear, wherein the third clutch is mounted between the second ring gear and the second shaft, wherein the fourth clutch is mounted between the first planet carrier and the first transfer drive gear, and wherein the first brake mounted between the first sun gear and the transmission housing.

The second clutch is mounted between the first ring gear and the first transfer drive gear.

The third clutch is mounted between the second ring gear and the first transfer driven gear.

The fourth clutch is mounted between the first transfer drive gear and the second transfer drive gear.

A first forward speed is achieved by operating the first brake and the first and second clutches, a second forward speed is achieved by operating the first brake and the first and fourth clutches, a third forward speed is achieved by operating first, second, and fourth clutches, a fourth forward speed is achieved by operating the first, third, and fourth clutches, a fifth forward speed is achieved by operating the first, second, and third clutches, a sixth forward speed is achieved by operating the second, third, and fourth clutches, a seventh forward speed is achieved by operating the first brake and the second and third clutches, an eighth forward speed is achieved by operating the first brake and the third and fourth clutches, and a reverse speed is achieved by operating the first brake and the first and third clutches.

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.

FIG. 1 is a schematic diagram of a planetary gear train according to an exemplary embodiment of the present invention.

FIG. 2 is an operational chart of friction members at each shift-speed applied to a planetary gear train according to an exemplary embodiment of the present invention.

FIG. 3A is a lever diagram of a planetary gear train at the first forward speed according to an exemplary embodiment of the present invention.

FIG. 3B is a lever diagram of a planetary gear train at the second forward speed according to an exemplary embodiment of the present invention.

FIG. 3C is a lever diagram of a planetary gear train at the third forward speed according to an exemplary embodiment of the present invention.

FIG. 3D is a lever diagram of a planetary gear train at the fourth forward speed according to an exemplary embodiment of the present invention.

FIG. 3E is a lever diagram of a planetary gear train at the fifth forward speed according to an exemplary embodiment of the present invention.

FIG. 3F is a lever diagram of a planetary gear train at the sixth forward speed according to an exemplary embodiment of the present invention.

FIG. 3G is a lever diagram of a planetary gear train at the seventh forward speed according to an exemplary embodiment of the present invention.

FIG. 3H is a lever diagram of a planetary gear train at the eighth forward speed according to an exemplary embodiment of the present invention.

FIG. 3I is a lever diagram of a planetary gear train at a reverse speed according to an 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.

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.

An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings.

Description of components that are not necessary for explaining the present exemplary embodiment 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 planetary gear train according to an exemplary embodiment of the present invention.

Referring to FIG. 1 , a planetary gear train according to an exemplary embodiment of the present invention includes first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 , five frictional elements B 1 , C 1 , C 2 , C 3 , and C 4 , and three transfer gears TF 1 , TF 2 , and TF 3 .

The first planetary gear set PG 1 is disposed on a first shaft IS 1 , and the second and third planetary gear sets PG 2 and PG 3 are disposed on a second shaft IS 2 disposed apart from and in parallel with the first shaft IS 1 .

The first shaft IS 1 is an input member and supports the first planetary gear set PG 1 , and torque transmitted from an engine is transmitted to the first planetary gear set PG 1 .

The second shaft 1 S 2 supports the second and third planetary gear sets PG 2 and PG 3 and transmits torque selectively transmitted from the first shaft IS 1 and the first and second planetary gear sets PG 1 and PG 2 to the third planetary gear set PG 3 .

Therefore, torque input from the first shaft IS 1 is converted into eight forward speeds and one reverse speed by operations of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 , and is then output through an output gear OG.

The first planetary gear set PG 1 is a double pinion planetary gear set, and having a first sun gear S 1 , a first ring gear R 1 , and a first planet carrier PC 1 rotatably supporting a pair of first pinions P 1 engaged with the first sun gear S 1 and the first ring gear R 1 as rotation elements thereof.

The second planetary gear set PG 2 is a single pinion planetary gear set, and having a second sun gear S 2 , a second ring gear R 2 , and a second planet carrier PC 2 rotatably supporting a second pinion P 2 engaged with the second sun gear S 2 and the second ring gear R 2 as rotation elements thereof.

The third planetary gear set PG 3 is a single pinion planetary gear set, and having a third sun gear S 3 , a third ring gear R 3 , and a third planet carrier PG 3 rotatably supporting a third pinion P 3 engaged with the third sun gear S 3 and the third ring gear R 3 as rotation elements thereof.

The first ring gear R 1 is directly connected to the first shaft IS 1 , the second planet carrier PC 2 is directly connected to the third planet carrier PC 3 , the third sun gear S 3 is directly connected to the second shaft IS 2 , and the third planet carrier PC 3 is directly connected to the output gear OG. In addition, the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 are combined by first, second, and third transfer gears TF 1 , TF 2 , and TF 3 and frictional elements including a first brake B 1 and first, second, third, and fourth clutches C 1 , C 2 , C 3 , and C 4 .

The first, second, and third transfer gears TF 1 , TF 2 , and TF 3 respectively have first, second, and third transfer drive gears TF 1 a , TF 2 a , and TF 3 a and first, second, and third transfer driven gears TF 1 b , TE 2 b , and TF 3 b externally meshed with each other.

The first transfer gear TF 1 connects the first shaft IS 1 with the second shaft IS 2 .

The second transfer gear TF 2 connects the first planet carrier PC 1 with the second sun gear S 2 .

The third transfer gear TF 3 connects the first sun gear S 1 with the third ring gear R 3 .

The first shaft IS 1 or rotation elements of the first planetary gear set PG 1 and rotation elements of the second planetary gear set PG 2 or the third planetary gear set PG 3 connected by the first, second, and third transfer gears TF 1 , TF 2 , and TF 3 are rotated in opposite directions to each other. Gear ratios of the first, second, and third transfer drive gears TF 1 a , TF 2 a , and TF 3 a and the first, second, and third transfer driven gears TF 1 b , TF 2 b , and TF 3 b are set according to speed ratios demanded at shift-speeds.

Arrangements of the frictional elements B 1 , C 1 , C 2 , C 3 , and C 4 will be described in detail.

The first brake B 1 is disposed between the first sun gear S 1 and a transmission housing H.

The first clutch C 1 is disposed between the first sun gear S 1 and the third transfer drive gear TF 3 a.

The second clutch C 2 is disposed between the first shaft IS 1 and the first transfer drive gear TF 1 a.

The third clutch C 3 is disposed between the second ring gear R 2 and the second shaft IS 2 .

The fourth clutch C 4 is disposed between the first planet carrier PC 1 and the first transfer drive gear IT 1 a.

The frictional elements including the first, second, third, and fourth clutches C 1 , C 2 , C 3 , and C 4 and the first brake G 1 are conventional multi-plate friction elements of wet type that are operated by hydraulic pressure.

FIG. 2 is an operational chart of friction members at each shift-speed applied to a planetary gear train according to an exemplary embodiment of the present invention.

As shown in FIG. 2 , three frictional elements are operated at each shift-speed in the planetary gear train according to an exemplary embodiment of the present invention.

A first forward speed 1ST is achieved by operating the first brake B 1 and the first and second clutches C 1 and C 2 .

A second forward speed 2ND is achieved by operating the first brake B 1 and the first and fourth clutches C 1 and C 4 .

A third forward speed 3RD is achieved by operating the first, second, and fourth clutches C 1 , C 2 , and C 4 .

A fourth forward speed 4TH is achieved by operating the first, third, and fourth clutches C 1 , C 3 , and C 4 .

A fifth forward speed 5TH is achieved by operating the first, second, and third clutches C 1 , C 2 , and C 3 .

A sixth forward speed 6TH is achieved by operating the second, third, and fourth clutches C 2 , C 3 , and C 4 .

A seventh forward speed 7TH is achieved by operating the first brake B 1 and the second and third clutches C 2 and C 3 .

An eighth forward speed 8TH is achieved by operating the first brake B 1 and the third and fourth clutches C 3 and C 4 .

A reverse speed REV is achieved by operating the first brake B 1 and the first and third clutches C 1 and C 3 .

FIG. 3A to FIG. 3I are lever diagrams of the planetary gear train at each shift-speed according to the various exemplary embodiments of the present invention, and illustrate shift processes of the planetary gear train according to the various exemplary embodiments of the present invention by lever analysis method.

Referring to FIG. 3A to FIG. 3I , three vertical lines of the first planetary gear set PG 1 are set as the first sun gear S 1 , the first ring gear R 1 , and the first planet carrier PC 1 from the left to the right, three vertical lines of the second planetary gear set PG 2 are set as the second sun gear S 2 , the second planet carrier PC 2 , and the second ring gear R 2 from the left to the right, and three vertical lines of the third planetary gear set PG 3 are set as the third sun gear S 3 , the third planet carrier PC 3 , and the third ring gear R 3 from the left to the right.

In addition, a middle horizontal line represents a rotation speed of “0”, an upper horizontal line represents a rotation speed of “1.0”, and a lower horizontal line represents a rotation speed of “−1.0”.

“−” means that rotational elements is rotated in an opposite direction of a rotational direction of the engine. It is because the first shaft IS 1 and the first planetary gear set PG 1 are externally meshed with the second planetary gear set PG 2 and the third planetary gear set PG 3 through the first, second, and third transfer gears TF 1 , TF 2 , and TF 3 without an idling gear.

In addition, the rotation speed of “1.0” represents the same rotational speed as the first shaft IS 1 which is an input shaft. Distances between the vertical lines of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 are set according to each gear ratio (teeth number of a sun gear/teeth number of a ring gear).

Hereinafter, referring to FIG. 2 and FIG. 3A to FIG. 3I , the shift processes of the planetary gear train according to an exemplary embodiment of the present invention will be described in detail.

[First Forward Speed]

Referring to FIG. 2 , the first brake B 1 and the first and second clutches C 1 and C 2 are operated at the first forward speed 1ST.

As shown in FIG. 3A , the rotation speed of the first shaft IS 1 is input to the first ring gear R 1 , and the rotation speed of the first shaft IS 1 is reduced by the gear ratio of the first transfer gear TF 1 and is then input to the third sun gear S 3 as an inverse rotation speed by operation of the second clutch C 2 .

At this state, the first sun gear S 1 and the third ring gear R 3 are operated as fixed elements by operation of the first brake B 1 and the first clutch C 1 . Therefore, the rotation elements of the third planetary gear set PG 3 form a first shift line SP 1 such that D 1 is output through the third planet carrier PC 3 .

At this time, the rotation speed of the first planet carrier PC 1 is increased according to the gear ratio of the second transfer gear TF 2 and is then input to the second sun gear S 2 , but it does not have any effect on shifting.

[Second Forward Speed]

The second clutch C 2 that was operated at the first forward speed 1ST is released and the fourth clutch C 4 is operated at the second forward speed 2ND.

As shown in FIG. 3B , the rotation speed of the first shaft IS 1 is input to the first ring gear R 1 , and the first sun gear S 1 and the third ring gear R 3 are operated as the fixed elements by operation of the first brake B 1 and the first clutch C 1 .

Therefore, the rotation speed of the first planet carrier PC 1 is reduced according to the gear ratio of the first transfer gear TF 1 by operation of the fourth clutch C 4 and is then input to the third sun gear S 3 as an inverse rotation speed.

In a state that the inverse rotation speed is input to the third sun gear S 3 , the third ring gear R 3 is operated as a fixed element in the third planetary gear set PG 3 . Therefore, the rotation elements of the third planetary gear set PG 3 form a second shift line SP 2 such that D 2 is output through the third planet carrier PC 3 .

At this time, the rotation speed of the first planet carrier PC 1 is increased according to the gear ratio of the second transfer gear TF 2 and is then input to the second sun gear S 2 , but it does not have any effect on shifting.

[Third Forward Speed]

The first brake B 1 that was operated at the second forward speed 2ND is released and the second clutch C 2 is operated at the third forward speed 3RD.

As shown in FIG. 3C , the rotation speed of the first shaft IS 1 is input to the first ring gear R 1 , and the rotation speed of the first shaft IS 1 is reduced according to the gear ratio of the first transfer gear TF 1 and is then input to the third sun gear S 3 as an inverse rotation speed by operation of the second clutch C 2 .

At this time, the first planetary gear set PG 1 becomes a direct-coupling state by operation of the second and fourth clutches C 2 and C 4 , and the rotation speed of the first sun gear S 1 is reduced according to the gear ratio of the third transfer gear TF 3 and is then input to the third ring gear R 3 as an inverse rotation speed by operation of the first clutch C 1 .

Therefore, the rotation elements of the third planetary gear set PG 3 form a third shift line SP 3 such that D 3 is output through the third planet carrier PC 3 .

At this time, the rotation speed of the first planet carrier PC 1 is increased according to the gear ratio of the second transfer gear TF 2 and is then input to the second sun gear S 2 , but it does not have any effect on shifting.

[Fourth Forward Speed]

The second clutch C 2 that was operated at the third forward speed 3RD is released and the third clutch C 3 is operated at the fourth forward speed 4TH.

As shown in FIG. 3I ), the rotation speed of the first shaft IS 1 is input to the first ring gear R 1 , and the rotation speed of the first sun gear S 1 is reduced according to the gear ratio of the third transfer gear TF 3 and is then input to the third ring gear R 3 as an inverse rotation speed by operation of the first clutch C 1 .

In addition, the rotation speed of the first planet carrier PC 1 is reduced according to the gear ratio of the first transfer gear TF 1 and is then input to the third sun gear S 3 as an inverse rotation speed by operation of the fourth clutch C 4 , and is increased according to the gear ratio of the second transfer gear TF 2 and is then input to the second sun gear S 2 as an inverse rotation speed.

At this state, the second ring gear R 2 is connected to the third sun gear S 3 by operation of the third clutch C 3 . Therefore, the rotation elements of the third planetary gear set PG 3 form a fourth shift line SP 4 such that D 4 is output through the third planet carrier PC 3 .

[Fifth Forward Speed]

The fourth clutch C 4 that was operated at the fourth forward speed 4TH is released and the second clutch C 2 is operated at the fifth forward speed 5TH.

As shown in FIG. 3E , the rotation speed of the first shaft IS 1 is input to the first ring gear R 1 , and the rotation speed of the first shaft IS 1 is reduced according to the gear ratio of the first transfer gear TF 1 and is then input to the third sun gear S 3 as an inverse rotation speed by operation of the second clutch C 2 .

In addition, the rotation speed of the first planet carrier PC 1 is increased according to the gear ratio of the second transfer gear TF 2 and is then input to the second sun gear 52 as an inverse rotation speed, and the rotation speed of the first sun gear S 1 is reduced according to the gear ratio of the third transfer gear TF 3 and is then input to the third ring gear R 3 as an inverse rotation speed by operation of the first clutch C 1 .

At this state, the second ring gear R 2 is connected to the third sun gear S 3 by operation of the third clutch C 3 . Therefore, the rotation elements of the third planetary gear set PG 3 form a fifth shift line SP 5 such that D 5 is output through the third planet carrier PC 3 .

[Sixth Forward Speed]

The first clutch C 1 that was operated at the fifth forward speed 5TH is released and the fourth clutch C 4 is operated at the sixth forward speed 6TH.

As shown in FIG. 3F , the rotation speed of the first shaft IS 1 is input to the first ring gear R 1 , and the rotation speed of the first shaft IS 1 is reduced according to the gear ratio of the first transfer gear TF 1 and is then input to the third sun gear S 3 as an inverse rotation speed by operation of the second clutch C 2 .

At this time, the first planetary gear set PC 1 becomes the direct-coupling state by operation of the second and fourth clutches C 2 and C 4 , and the rotation speed of the first planet carrier PC 1 is increased according to the gear ratio of the second transfer gear TF 2 and is then input to the second sun gear S 2 as an inverse rotation speed.

At this state, the second ring gear R 2 is connected to the third sun gear S 3 by operation of the third clutch C 3 . Therefore, the rotation elements of the third planetary gear set PG 3 form a sixth shift line SP 6 such that D 6 is output through the third planet carrier PC 3 .

[Seventh Forward Speed]

The fourth clutch C 4 that was operated at the sixth forward speed 6TH is released and the first brake B 1 is operated at the seventh forward speed 7TH.

As shown in FIG. 3G , the rotation speed of the first shaft IS 1 is input to the first ring gear R 1 , and the rotation speed of the first shaft IS 1 is reduced according to the gear ratio of the first transfer gear TF 1 and is then input to the third sun gear S 3 as an inverse rotation speed by operation of the second clutch C 2 .

In addition, the first sun gear S 1 is operated as a fixed element by operation of the first brake B 1 , and the rotation speed of the first planet carrier PC 1 is increased according to the gear ratio of the second transfer gear TF 2 and is then input to the second sun gear S 2 as an inverse rotation speed.

At this state, the second ring gear R 2 is connected to the third sun gear S 3 by operation of the third clutch C 3 . Therefore, the rotation elements of the third planetary gear set PG 3 form a seventh shift line SP 7 such that D 7 is output through the third planet carrier PC 3 .

[Eighth Forward Speed]

The second clutch C 2 that was operated at the seventh forward speed 7TH is released and the fourth clutch C 4 is operated at the eighth forward speed 8TH.

As shown in FIG. 3H , the rotation speed of the first shaft IS 1 is input to the first ring gear R 1 and the first sun gear S 1 is operated as a fixed element by operation of the first brake B 1 .

Therefore, the rotation speed of the first planet carrier PC 1 is reduced according to the gear ratio of the first transfer gear TF 1 and is then input to the third sun gear S 3 as an inverse rotation speed by operation of the fourth clutch C 4 , and is increased according to the gear ratio of the second transfer gear TF 2 and is then input to the second sun gear S 2 as an inverse rotation speed.

At this state, the second ring gear R 2 is connected to the third sun gear S 3 by operation of the third clutch C 3 . Therefore, the rotation elements of the third planetary gear set PG 3 form an eighth shift line SP 8 such that D 8 is output through the third planet carrier PC 3 .

[Reverse Speed]

As shown in FIG. 2 , the first brake B 1 and the first and third clutches C 1 and C 3 are operated at the reverse speed REV.

As shown in FIG. 3I , the rotation speed of the first shaft IS 1 is input to the first ring gear R 1 , and the first sun gear S 1 and the third ring gear R 3 are operated as fixed elements by operation of the first brake B 1 and the first clutch C 1 .

In addition, the rotation speed of the first planet carrier PC 1 is increased according to the gear ratio of the second transfer gear TF 2 and is then input to the second sun gear S 2 as an inverse rotation speed, and the second ring gear R 2 is connected to the third sun gear S 3 by operation of the third clutch C 1 .

Therefore, the rotation elements of the third planetary gear set PG 3 form a reverse shift line RS such that REV is output through the third planet carrier PC 3 .

Since three planetary gear sets are separately disposed on the first shaft and the second shaft disposed apart from and in parallel with each other in the planetary gear train according to an exemplary embodiment of the present invention, a length thereof may be reduced and mountability may be improved.

In addition, optimum gear ratios may be set due to ease of changing gear ratios by using three external-meshing gears as well as the planetary gear sets. Since gear ratios can be changed according to target performance, starting performance may be improved. Therefore, a start-up clutch instead of a torque converter may be used.

Since three frictional elements are operated at each shift-speed, non-operated frictional element may be minimized and drag torque may be reduced. In addition, fuel consumption may be reduced by increasing power delivery efficiency.

In addition, since torque load of each frictional element can be reduced, compact design is possible.

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. 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, 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.