Planetary gear train of automatic transmission for vehicles

An automatic transmission planetary gear train for a vehicle may include a first shaft receiving a torque of an engine, a second shaft disposed substantially in parallel with the first shaft, a first planetary gear set disposed on the first shaft and including a first sun gear, a first planet carrier, and a first ring gear as rotation elements, a second planetary gear set disposed on the second shaft and including a second sun gear, a second planet carrier, and a second ring gear as rotation elements, a third planetary gear set disposed on the second shaft and including a third sun gear, a third planet carrier, and a third ring gear as rotation elements, three transfer gears forming the externally-meshed gears, and frictional elements selectively interconnecting the rotation elements of the first, second, and third planetary gear sets or selectively connecting a rotation element to a transmission housing.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority of Korean Patent Application Number 10-2012-0124111 filed Nov. 5, 2012, the entire contents of which application are incorporated herein for all purposes by this reference.

BACKGROUND OF INVENTION

1. Field of 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

Recently, vehicle makers direct all their strength to improve fuel economy due to worldwide high oil prices and strengthen of exhaust gas regulations.

Improvement of fuel economy may be achieved by multi-shift mechanism realizing greater number of shift speeds in an automatic transmission. Typically, a planetary gear train is realized by combining a plurality of planetary gear sets and friction elements.

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 as a durability, power delivery efficiency, and size, that depend on the layout thereof. Therefore, designs for a combining structure of a gear train are also under continuous investigation.

If the number of shift-speeds, however, increases, the number of components in the automatic transmission also increases. Therefore, mountability, cost, weight and power delivery efficiency may be deteriorated.

Particularly, since the planetary gear train having a number of components is hard to be mounted in a front wheel drive vehicle, researches for minimizing the number of components have been developed.

SUMMARY OF INVENTION

The present invention has been made in an effort to provide 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.

A planetary gear train of an automatic transmission for a vehicle according to various aspects of the present invention may include: a first shaft receiving a torque of an engine; a second shaft disposed substantially in parallel with the first shaft; a first planetary gear set disposed on the first shaft, and including a first sun gear operated as an output element or a fixed element, a first planet carrier directly connected to the first shaft and operated as an input element, and a first ring gear operated as an output element, wherein the first sun gear, the first planet carrier and the first ring gear are rotation elements thereof; a second planetary gear set disposed on the second shaft, and including a second sun gear connected to the first ring gear through an externally-meshed gear, a second planet carrier, and a second ring gear selectively connected to the first planet carrier and the first ring gear through externally-meshed gears, wherein the second sun gear, the second planet carrier, and the second ring gear are rotation elements thereof; a third planetary gear set disposed on the second shaft, and including a third sun gear connected to the second ring gear, a third planet carrier selectively connected to the second planet carrier and directly connected to an output gear to be operated as an output element, and a third ring gear selectively connected to the first sun gear through an externally-meshed gear, wherein the third sun gear, the third planet carrier and the third ring gear are rotation elements thereof; three transfer gears forming the externally-meshed gears; and frictional elements selectively interconnecting the rotation elements of the first, second, and third planetary gear sets or selectively connecting at least one rotation element to a transmission housing.

Each of the first, second, and third planetary gear sets may be a single pinion planetary gear set.

The three transfer gears may include: a first transfer gear selectively connecting the first planet carrier to the second ring gear; a second transfer gear connecting the first ring gear directly to the second sun gear and selectively to the second ring gear; and a third transfer gear selectively connecting the first sun gear to the third ring gear.

The frictional elements may include: a first brake disposed between the first sun gear and the transmission housing; a first clutch disposed between the first sun gear and the third transfer gear; a second clutch disposed between the second transfer gear and the second ring gear; a third clutch disposed between the second planet carrier and the third planet carrier; and a fourth clutch disposed between the first transfer gear and the second ring gear.

The first brake and the first and fourth clutches may be operated at a first forward speed, the first brake and the first and second clutches may be operated at a second forward speed, the first, second, and fourth clutches may be operated at a third forward speed, the first, second, and third clutches may be operated at a fourth forward speed, the first, third, and fourth clutches may be operated at a fifth forward speed, the second, third, and fourth clutches may be operated at a sixth forward speed, the first brake and the third and fourth clutches may be operated at a seventh forward speed, the first brake and the second and third clutches may be operated at an eighth forward speed, and the first brake and the first and third clutches may be operated at a reverse speed.

A planetary gear train of an automatic transmission for a vehicle according to various other aspects of the present invention may include: a first shaft receiving a torque of an engine; a second shaft disposed substantially in parallel with the first shaft; a first planetary gear set disposed on the first shaft, and including a first sun gear operated as an output element or a fixed element, a first planet carrier directly connected to the first shaft and always operated as an input element, and a first ring gear operated as an output element; a second planetary gear set disposed on the second shaft, and including a second sun gear connected to the first ring gear, a second planet carrier, and a second ring gear selectively connected to the first planet carrier and the first ring gear; a third planetary gear set disposed on the second shaft, and including a third sun gear connected to the second ring gear, a third planet carrier selectively connected to the second planet carrier and directly connected to an output gear to be operated as an output element, and a third ring gear selectively connected to the first sun gear; a first transfer gear selectively connecting the first planet carrier to the second ring gear; a second transfer gear connecting the first ring gear directly to the second sun gear and selectively to the second ring gear; a third transfer gear selectively connecting the first sun gear to the third ring gear; a first brake disposed between the first sun gear and the transmission housing; a first clutch disposed between the first sun gear and the third transfer gear; a second clutch disposed between the second transfer gear and the second ring gear; a third clutch disposed between the second planet carrier and the third planet carrier; and a fourth clutch disposed between the first transfer gear and the second ring gear.

The first brake and the first and fourth clutches may be operated at a first forward speed, the first brake and the first and second clutches may be operated at a second forward speed, the first, second, and fourth clutches may be operated at a third forward speed, the first, second, and third clutches may be operated at a fourth forward speed, the first, third, and fourth clutches may be operated at a fifth forward speed, the second, third, and fourth clutches may be operated at a sixth forward speed, the first brake and the third and fourth clutches may be operated at a seventh forward speed, the first brake and the second and third clutches may be operated at an eighth forward speed, and the first brake and the first and third clutches may be operated at a reverse speed.

DETAILED DESCRIPTION

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. 1is a schematic diagram of a planetary gear train according to various embodiments of the present invention. Referring toFIG. 1, a planetary gear train includes first, second, and third planetary gear sets PG1, PG2, and PG3, five frictional elements B1, C1, C2, C3, and C4, and three transfer gears TF1, TF2, and TF3.

The first planetary gear set PG1is disposed on a first shaft IS1, and the second and third planetary gear sets PG2and PG3are disposed on a second shaft IS2, which is disposed apart from and substantially in parallel with the first shaft IS1.

Therefore, torque input from the first shaft IS1is transmitted to the second and third planetary gear sets PG2and PG3through the first planetary gear set PG1, is converted into eight forward speeds and one reverse speed by operations of the first, second, and third planetary gear sets PG1, PG2, and PG3, and is then output through an output gear OG.

The first planetary gear set PG1is a single pinion planetary gear set, and has a first sun gear S1, a first ring gear R1, and a first planet carrier PC1rotatably supporting a first pinion P1engaged with the first sun gear S1and the first ring gear R1. The first sun gear S1, the first ring gear R1, and/or the first planet carrier PC1are rotation elements of the first planetary gear set PG1.

The second planetary gear set PG2is a single pinion planetary gear set, and has a second sun gear S2, a second ring gear R2, and a second planet carrier PC2rotatably supporting a second pinion P2engaged with the second sun gear S2and the second ring gear R2. The second sun gear S2, the second ring gear R2, and/or the second planet carrier PC2are rotation elements of the second planetary gear set PG2.

The third planetary gear set PG3is a single pinion planetary gear set, and has a third sun gear S3, a third ring gear R3, and a third planet carrier PC3rotatably supporting a third pinion P3engaged with the third sun gear S3and the third ring gear R3. The third sun gear S3, the third ring gear R3, and/or the third planet carrier PC3are rotation elements of the third planetary gear set PG3.

The first planet carrier PC1is directly connected to the first shaft IS1and is operated, and in some cases is always operated, as an input element.

In addition, the second ring gear R2is connected to the third sun gear S3through the second shaft IS2, the second planet carrier PC2is selectively connected to the third planet carrier PC3, and the third planet carrier PC3is directly connected to an output gear OG and is operated, and in some cases is always operated, as an output element.

It is illustrated, but is not limited to, that the second ring gear R2is connected to the third sun gear S3through the second shaft IS2. That is, in some cases, the second ring gear R2may be connected to the third sun gear S3through a rotating member disposed on an external circumferential portion of the second shaft IS2without rotational interference between the rotating member and the second shaft IS2.

In addition, the first planet carrier PC1as well as the first shaft IS1is selectively connected to the second ring gear R2through an externally-meshed gear, the first sun gear S1is selectively connected to the third ring gear R3through an externally-meshed gear and is selectively connected to a transmission housing H, and the first ring gear R1is connected to the second sun gear S2through an externally-meshed gear and is selectively connected to the second ring gear R2through an externally-meshed gear.

The first, second, and third transfer gears TF1, TF2, and TF3, being the externally-meshed gears, may be helical gears and respectively have first, second, and third transfer drive gears TF1a, TF2a, and TF3aand first, second, and third transfer driven gears TF1b, TF2b, and TF3bexternally meshed with each other.

The first transfer gear TF1includes the first transfer drive gear TF1adirectly connected to the first planet carrier PC1and the first transfer driven gear TF1bselectively connected to the second ring gear R2. Therefore, the first transfer gear TF1selectively connects the first planet carrier PC1with the second ring gear R2.

The second transfer gear TF2includes the second transfer drive gear TF2adirectly connected to the first ring gear R1and the second transfer driven gear TF2bdirectly connected to the second sun gear S2and selectively connected to the second ring gear R2. Therefore, the second transfer gear TF2connects the first ring gear R1directly to the second sun gear S2and selectively to the second ring gear R2.

The third transfer gear TF3includes the third transfer drive gear TF3aselectively connected to the first sun gear S1and the third transfer driven gear TF3bdirectly connected to the third ring gear R3. Therefore, the third transfer gear TF3selectively connects the first sun gear S1to the third ring gear R3.

The rotation elements connected to each other by the first, second, and third transfer gears TF1, TF2, and TF3are rotated in opposite directions with respect to each other. Gear ratios of the first, second, and third transfer gears TF1, TF2, and TF3are set according to speed ratios demanded at shift-speeds.

Arrangements of the frictional elements B1, C1, C2, C3, and C4will be described in detail.

The first brake B1is disposed between the first sun gear S1and the transmission housing H. The first clutch C1is disposed between the first sun gear S1and the third transfer gear TF3. The second clutch C2is disposed between the second transfer gear TF2and the second ring gear R2. The third clutch C3is disposed between the second planet carrier PC2and the third planet carrier PC3. The fourth clutch C4is disposed between the first transfer gear TF1and the second ring gear R2.

The frictional elements consisting of the first, second, third, and fourth clutches C1, C2, C3, and C4and the first brake B1are conventional multi-plate friction elements of wet type that are operated by hydraulic pressure.

FIG. 2is an operational chart of friction members at each shift-speed applied to a planetary gear train according to various embodiments of the present invention. As shown inFIG. 2, three frictional elements are operated at each shift-speed in the planetary gear train according to various embodiments of the present invention.

The first brake B1and the first and fourth clutches C1and C4are operated at a first forward speed 1ST. The first brake B1and the first and second clutches C1and C2are operated at a second forward speed 2ND. The first, second, and fourth clutches C1, C2, and C4are operated at a third forward speed 3RD. The first, second, and third clutches C1, C2, and C3are operated at a fourth forward speed 4TH. The first, third, and fourth clutches C1, C3, and C4are operated at a fifth forward speed 5TH. The second, third, and fourth clutches C2, C3, and C4are operated at a sixth forward speed 6TH. The first brake B1and the third and fourth clutches C3and C4are operated at a seventh forward speed 7TH. The first brake B1and the second and third clutches C2and C3are operated at an eighth forward speed 8TH. The first brake B1and the first and third clutches C1and C3are operated at a reverse speed Rev.

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

Referring toFIG. 3AtoFIG. 3I, three vertical lines of the first planetary gear set PG1are set to graphically represent the first sun gear S1being a first rotation element N1, the first planet carrier PC1being a second rotation element N2, and the first ring gear R1being a third rotation element N3from the left to the right.

In addition, the second and third planetary gear sets PG2and PG3are operated as a selective compound planetary gear set according to operation of the third clutch C3. Four vertical lines of the second and third planetary gear sets PG2and PG3are set to graphically represent the second sun gear S2being a fourth rotation element N4, the third ring gear R3being a fifth rotation element N5, the third planet carrier PC3or the second planet carrier PC2and the third planet carrier PC3being a sixth rotation element N6, and the second ring gear R2and the third sun gear S3being a seventh rotation element N7from the left to the right.

Since the third clutch C3is not operated from the first forward speed to the third forward speed, the third planet carrier PC3is set as the sixth rotation element N6. Since the third clutch C3is operated from the fourth forward speed to the eighth forward speed and at the reverse speed, however, the second and third planet carriers PC2and PC3are set as the sixth rotation element N6.

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 a rotational element is rotated in an opposite direction of a rotational direction of the engine. It is because the rotation elements are externally meshed with each other through the first, second, and third transfer gears TF1, TF2, and TF3without an idling gear.

In addition, the rotation speed of “1.0” represents the same rotational speed as the first shaft IS1which is an input shaft. Distances between the vertical lines of the first, second, and third planetary gear sets PG1, PG2, and PG3are set approximately or substantially according to each gear ratio (teeth number of a sun gear/teeth number of a ring gear).

Hereinafter, referring toFIG. 2andFIG. 3AtoFIG. 3I, the shift processes of the planetary gear train according to various embodiments of the present invention will be described in detail.

First Forward Speed

Referring toFIG. 2, the first brake B1and the first and fourth clutches C1and C4are operated at the first forward speed 1ST.

As shown inFIG. 3A, a rotation speed of the first shaft IS1is input to the second rotation element N2, and the first rotation element N1and the fifth rotation element N5are operated as fixed elements by operation of the first brake B1and the first clutch C1.

Therefore, a rotation speed of the third rotation element N3is decreased according to the gear ratio of the second transfer gear TF2and is then input to the fourth rotation element N4as an inverse rotation speed, and the rotation speed of the first shaft IS1is changed according to the gear ratio of the first transfer gear TF1by operation of the fourth clutch C4and is then input to the seventh rotation element N7as an inverse rotation speed.

Therefore, the rotation elements of the third planetary gear set PG3form a first shift line SP1and D1is output through the sixth rotation element N6that is the output element. At this time, the rotation elements of the second planetary gear set PG2form a thick dotted line T, but it does not have any effect on shifting.

Second Forward Speed

The fourth clutch C4that was operated at the first forward speed 1STis released and the second clutch C2is operated at the second forward speed 2ND.

As shown inFIG. 3B, the rotation speed of the first shaft IS1is input to the second rotation element N2, and the first rotation element N1and the fifth rotation element N5are operated as the fixed elements by operation of the first brake B1and the first clutch C1.

Therefore, a rotation speed of the third rotation element N3is decreased according to the gear ratio of the second transfer gear TF2and is then input to the fourth rotation element N4as an inverse rotation speed, and the second planetary gear set PG2becomes direct-coupling state by operation of the second clutch C2.

Therefore, the rotation elements of the third planetary gear set PG3form a second shift line SP2and D2is output through the sixth rotation element N6that is the output element. At this time, the rotation elements of the second planetary gear set PG2form a thick dotted line T, but it does not have any effect on shifting.

Third Forward Speed

The first brake B1that was operated at the second forward speed 2NDis released and the fourth clutch C4is operated at the third forward speed 3RD.

As shown inFIG. 3C, the rotation speed of the first shaft IS1is input to the second rotation element N2, the third rotation element N3is connected to the fourth rotation element N4through the second transfer gear TF2, the first rotation element N1is connected to the fifth rotation element N5through the third transfer gear TF3by operation of the first clutch C1, and the second rotation element N2is connected to the seventh rotation element N7through the first transfer gear TF1by operation of the fourth clutch C4.

Therefore, the rotation elements of the third planetary gear set PG3form a third shift line SP3and D3is output through the sixth rotation element N6that is the output element. At this time, the rotation elements of the second planetary gear set PG2form a thick dotted line T, but it does not have any effect on shifting.

Fourth Forward Speed

The fourth clutch C4that was operated at the third forward speed 3RDis released and the third clutch C3is operated at the fourth forward speed 4TH.

As shown inFIG. 3D, the rotation speed of the first shaft IS1is input to the second rotation element N2, the third rotation element N3is connected to the fourth rotation element N4through the second transfer gear TF2, the first rotation element N1is connected to the fifth rotation element N5through the third transfer gear TF3by operation of the first clutch C1, and the third rotation element N3is connected to the seventh rotation element N7through the second transfer gear TF2by operation of the second clutch C2.

Therefore, the second and third planetary gear sets PC2and PC3become direct-coupling states, the rotation elements of the second and third planetary gear sets PC2and PC3form a fourth shift line SP4, and D4is output through the sixth rotation element N6that is the output element.

Fifth Forward Speed

The second clutch C2that was operated at the fourth forward speed 4THis released and the fourth clutch C4is operated at the fifth forward speed 5TH.

As shown inFIG. 3E, the rotation speed of the first shaft IS1is input to the second rotation element N2and is input to the seventh rotation element N7through the first transfer gear TF1by operation of the fourth clutch C4.

In addition, the third rotation element N3is connected to the fourth rotation element N4through the second transfer gear TF2, and the first rotation element N1is connected to the fifth rotation element N5through the third transfer gear TF3by operation of the first clutch C1.

Therefore, the rotation elements of the second and third planetary gear sets PG2and PG3form a fifth shift line SP5and D5is output through the sixth rotation element N6that is the output element.

Sixth Forward Speed

The first clutch C1that was operated at the fifth forward speed 5THis released and the second clutch C2is operated at the sixth forward speed 6TH.

As shown inFIG. 3F, the rotation speed of the first shaft IS1is input to the second rotation element N2and is input to the seventh rotation element N7through the first transfer gear TF1by operation of the fourth clutch C4.

In addition, the third rotation element N3is connected to the fourth rotation element N4and is connected to the seventh rotation element N7by operation of the second clutch C2through the second transfer gear TF2.

Therefore, the second and third planetary gear sets PC2and PC3become the direct-coupling states, the rotation elements of the second and third planetary gear sets PC2and PC3form a sixth shift line SP6, and D6is output through the sixth rotation element N6that is the output element.

Seventh Forward Speed

The second clutch C2that was operated at the sixth forward speed 6THis released and the first brake B1is operated at the seventh forward speed 7TH.

As shown inFIG. 3G, the rotation speed of the first shaft IS1is input to the second rotation element N2and is input to the seventh rotation element N7through the first transfer gear TF1by operation of the fourth clutch C4, and the first rotation element N1is operated as the fixed element by operation of the first brake B1.

In addition, the third rotation element N3is connected to the fourth rotation element N4through the second transfer gear TF2.

Therefore, the rotation elements of the second and third planetary gear sets PG2and PG3form a seventh shift line SP7and D7is output through the sixth rotation element N6that is the output element.

Eighth Forward Speed

The fourth clutch C4that was operated at the seventh forward speed 7THis released and the second clutch C2is operated at the eighth forward speed 8TH.

As shown inFIG. 3H, the rotation speed of the first shaft IS1is input to the second rotation element N2, and the first rotation element N1is operated as the fixed element by operation of the first brake B1.

In addition, the third rotation element N3is connected to the fourth rotation element N4and is connected to the seventh rotation element N7by operation of the second clutch C2through the second transfer gear TF2.

Therefore, the second and third planetary gear sets PC2and PC3become the direct-coupling state, the rotation elements of the second and third planetary gear sets PC2and PC3form an eighth shift line SP8, and D8is output through the sixth rotation element N6that is the output element.

Reverse Speed

As shown inFIG. 2, the first brake B1and the first and third clutches C1and C3are operated at the reverse speed Rev.

As shown inFIG. 3I, the rotation speed of the first shaft IS1is input to the second rotation element N2, and the first rotation element N1and the fifth rotation element N5are operated as the fixed elements by operation of the first brake B1and the first clutch C1.

In addition, the third rotation element N3is connected to the fourth rotation element N4through the second transfer gear TF2.

Therefore, the rotation elements of the second and third planetary gear sets PG2and PG3form a reverse shift line RS and REV is output through the sixth rotation element N6that is the output element.

Since three planetary gear sets are separately disposed on the first shaft and the second shaft, which are disposed apart and substantially in parallel with each other, in the planetary gear train according to various embodiments 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.