Power train of automatic transmission

This application claims priority to and the benefit of Korean Patent Application No. 10-2006-0063080 filed in the Korean Intellectual Property Office on Jul. 5, 2006,the entire contents of which are incorporated herein by reference.

(a) Field of the Invention

The present invention relates to a power train of an automatic transmission. More particularly, the present invention relates to a power train of an automatic transmission that realizes seven forward speeds and two reverse speeds.

(b) Description of the Related Art

A typical shift mechanism of an automatic transmission utilizes a combination of a plurality of planetary gear sets. A power train of such an automatic transmission that includes the plurality of planetary gear sets changes rotating speed and torque received from a torque converter of the automatic transmission, and accordingly changes and 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 better fuel mileage and better performance.

For that reason, an automatic transmission that enables more shift speeds is under constant investigation.

In addition, with the same number of speeds, features of a power train such as durability, efficiency in power transmission, and size depend a lot on the layout of the combined planetary gear sets. Therefore, designs for a combining structure of a power train are also under constant investigation.

A manual transmission that has too many speeds causes an inconvenience of excessively frequent shifting operations to a driver. Therefore, the positive features of more shift-speeds are more important for automatic transmissions because an automatic transmission automatically controls shifting operations without needing any manual operation.

Recently, power trains of automatic transmissions that realize seven forward speeds have been developed. For example, U.S. Patent Laid-Open No. US2005/0113205 A1 discloses a power train of an automatic transmission that realizes seven forward speeds and one reverse speed by using four planetary gear sets, five brakes, and three clutches. However, since the power train of US2005/0113205 A1 includes four planetary gear sets, five brakes, and three clutches, the power train is heavy. In addition, it is difficult to dispose frictional elements such as brakes and clutches in the transmission according to the power train of US2005/0113205 A1.

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.

Embodiments of the present invention provide a power train of an automatic transmission having advantages of realizing seven forward speeds and two reverse speeds by using three planetary gear sets, three clutches, and four brakes.

An exemplary power train of an automatic transmission according to an embodiment of the present invention may include: a first planetary gear set having operating members of a first sun gear, a first ring gear, and a first planet carrier; a second planetary gear set having operating members of a second sun gear, a second ring gear, and a second planet carrier; a third planetary gear set having operating members of a third sun gear, a short-pinion-side ring gear, a long-pinion-side ring gear, and a third planet carrier; an input shaft; an output gear, and a transmission case. The third planet carrier is fixedly connected to the first ring gear, the second ring gear is fixedly connected to the first planet carrier, the long-pinion-side ring gear always acts as an input element by being fixedly connected to the input shaft, and the second planet carrier always acts as an output element by being fixedly connected to the output gear. Also, the second ring gear is variably connected to the input shaft via a first clutch, the first sun gear is variably connected to the first planet carrier via a second clutch, the second sun gear is variably connected to the first sun gear via a third clutch, and the short-pinion-side ring gear is variably connected to the transmission case via a first brake and is subjected to a stopping operation of the first brake. Further, at least one of the variably connected first sun gear and the second sun gear is variably connected to the transmission case via a second brake and is subjected to a stopping operation of the second brake, the third sun gear is variably connected to the transmission case via a third brake and is subjected to a stopping operation of the third brake, and the first planet carrier is variably connected to the transmission case via a fourth brake and is subjected to a stopping operation of the fourth brake.

The first, second, and third planetary gear sets may be disposed in a sequence of the third planetary gear set, the second planetary gear set, and the first planetary gear set.

The input shaft and the output gear may be disposed on the same side.

The first and third brakes may be disposed on the same side and the second and fourth brakes may be disposed on the same side.

The first and third brakes may be disposed on an opposite side to the second and fourth brakes with reference to the planetary gear sets.

The first clutch may be disposed between the second planetary gear set and the third planetary gear set, and the second and third clutches may be disposed on an opposite side to the first clutch with reference to the first planetary gear set.

The third clutch and the first and second brakes may be operated in a first forward speed; the third clutch and the second and third brakes be operated in a second forward speed; the second clutch and the second and third brakes be operated in a third forward speed; the second and third clutches and the third brake be operated in a fourth forward speed; the first, second, and third clutches be operated in a fifth forward speed, the first and third clutches and the third brake be operated in a sixth forward speed; the first and third clutches and the first brake be operated in a seventh forward speed; the third clutch and the first and fourth brakes be operated in a first reverse speed; and the third clutch and the third and fourth brakes be operated in a second reverse speed.

FIG. 1 is a schematic diagram of a power train of an automatic transmission according to an exemplary embodiment of the present invention.

FIG. 2 is an operational chart for a power train of an automatic transmission according to an exemplary embodiment of the present invention.

FIG. 3 is a lever diagram showing shifting processes from a first forward speed to a seventh forward speed, and from a first reverse speed to a second reverse speed in a power train of an automatic transmission according to an embodiment of the present invention.

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

As shown in FIG. 1 , an exemplary power train of an automatic transmission according to an embodiment of the present invention includes three planetary gear sets of first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 .

The first planetary gear set PG 1 is a single pinion planetary gear set, and includes a first sun gear S 1 , a first planet carrier PC 1 , and a first ring gear R 1 as operating members thereof. A first pinion gear P 1 , being engaged with both the first ring gear R 1 and the first sun gear S 1 , is connected to and carried by the first planet carrier PC 1 .

The second planetary gear set PG 2 is a single pinion planetary gear set, and includes a second sun gear S 2 , a second planet carrier PC 2 , and a second ring gear R 2 as operating members thereof. A second pinion gear P 2 , being engaged with the second-ring gear R 2 and the second sun gear S 2 , is connected to and carried by the second planet carrier PC 2 .

The third planetary gear set PG 3 is a compound planetary gear set, and includes a double pinion planetary gear set including a third sun gear S 3 , a short pinion gear SP, a long pinion gear LP, and a short-pinion-side ring gear SR, and a single pinion planetary gear set including the third sun gear S 3 , the long pinion gear LP, and a long-pinion-side ring gear LR. The third planetary gear set PG 3 further includes a third planet carrier PC 3 rotatably supporting the short pinion gear SP and the long pinion gear LP.

In addition, the third sun gear S 3 , the third planet carrier PC 3 , the short-pinion-side ring gear SR, and the long-pinion-side ring gear LR are used as operating members of the third planetary gear set PG 3 .

In addition, an exemplary power train of an automatic transmission according to an embodiment of the present invention includes an input shaft 100 for receiving torque from an engine (not shown), an output gear 200 for outputting torque from the power train, and a transmission case 300 .

As shown in FIG. 1 , the third planet carrier PC 3 is fixedly connected to the first ring gear R 1 . The second ring gear R 2 is fixedly connected to the first planet carrier PC 1 . The long-pinion-side ring gear LR always acts as an input element by being fixedly connected to the input shaft 100 . The second planet carrier PC 2 always acts as an output element by being fixedly connected to the output gear 200 . The second ring gear R 2 is variably connected to the input shaft 100 via a first clutch C 1 . The first sun gear S 1 is variably connected to the first planet carrier PC 1 via a second clutch C 2 .

The second sun gear S 2 is variably connected to the first sun gear S 1 via a third clutch C 3 . The short-pinion-side ring gear SR is variably connected to the transmission case 300 via a first brake B 1 and is subjected to a stopping operation of the first brake B 1 .

At least one of the variably connected first sun gear S 1 and the second sun gear S 2 is variably connected to the transmission case 300 via a second brake B 2 and is subjected to a stopping operation of the second brake B 2 . The third sun gear S 3 is variably connected to the transmission case 300 via a third brake B 3 and is subjected to a stopping operation of the third brake B 3 . The first planet carrier PC 1 is variably connected to the transmission case 300 via a fourth brake B 4 and is subjected to a stopping operation of the fourth brake B 4 .

The first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 are disposed in a sequence of the third planetary gear set PG 3 , the second planetary gear set PG 2 , and the first planetary gear set PG 1 according to an exemplary embodiment of an present invention.

The input shaft 100 and the output gear 200 are disposed on the same side. The first brake B 1 and the third brake B 3 are disposed on the same side. In addition, the second brake B 2 and the fourth brake B 4 are disposed on the same side.

In addition, the first brake B 1 and the third brake B 3 are disposed on an opposite side to the second brake B 2 and the fourth brake B 4 with reference to the planetary gear sets PG 1 , PG 2 , and PG 3 .

The first clutch C 1 is disposed between the second planetary gear set PG 2 and the third planetary gear set PG 3 , and the second clutch C 2 and the third clutch C 3 are disposed on an opposite side to the first clutch C 1 with reference to the first planetary gear set PG 1 .

Hereinafter, operation of power train of an automatic transmission according to the exemplary embodiment of the present invention will be described.

As shown in FIG. 2 , according to an exemplary embodiment of the present invention, the third clutch C 3 and the first and second brakes B 1 and B 2 are operated in a first forward speed D 1 , the third clutch C 3 and the second and third brakes B 2 and B 3 are operated in a second forward speed D 2 , the second clutch C 2 and the second and third brakes B 2 and B 3 are operated in a third forward speed D 3 , the second and third clutches C 2 and C 3 and the third brake B 3 are operated in a fourth forward speed D 4 , the first, second, and third clutches C 1 , C 2 , and C 3 are operated in a fifth forward speed D 5 , the first and third clutches C 1 and C 3 and the third brake B 3 are operated in a sixth forward speed, and the first and third clutches C 1 and C 3 and the first brake B 1 are operated in a seventh forward speed D 7 .

In addition, the third clutch C 3 and the first and fourth brakes B 1 and B 4 are operated in a first reverse speed REV. 1 and the third clutch C 3 and the third and fourth brakes B 3 and B 4 are operated in a second reverse speed REV. 2 .

Hereinafter, up-shifting processes of an exemplary power train of an automatic transmission according to the embodiment of the present invention will be described in detail.

In a shifting process from the first forward speed D 1 to the second forward speed D 2 , the first brake B 1 is released and the third brake B 3 is operated.

In a shifting process from the second forward speed D 2 to the third forward speed D 3 , the third clutch C 3 is released and the second clutch C 2 is operated.

In a shifting process from the third forward speed D 3 to the fourth forward speed D 4 , the second brake B 2 is released and the third clutch C 3 is operated.

In a shifting process from the fourth forward speed D 4 to the fifth forward speed D 5 , the third brake B 3 is released and the first clutch C 1 is operated.

In a shifting process from the fifth forward speed D 5 to the sixth forward speed D 6 , the second clutch C 2 is released and the third brake B 3 is operated.

In a shifting process from the sixth forward speed D 6 to the seventh forward speed D 7 , the third brake B 3 is released and the first brake B 1 is operated.

In a shifting process from the first reverse speed Rev. 1 to the second reverse speed Rev. 2 , the first brake B 1 is released and the third brake B 3 is operated.

Down-shifting processes are reverse processes of the up-shifting processes according to an exemplary embodiment of the present invention.

Hereinafter, skip up-shifting processes according to an exemplary embodiment of the present invention will be described.

In a skip up-shifting process from the first forward speed D 1 to the third forward speed D 3 , the third clutch C 3 and the first brake B 1 are released and the second clutch C 2 and the third brake B 3 are operated.

In a skip up-shifting process from the second forward speed D 2 to the fourth forward speed D 4 , the second brake B 2 is released and the second clutch C 2 is operated.

In a skip up-shifting process from the third forward speed D 3 to the fifth forward speed D 5 , the second and third brakes B 2 and B 3 are released and the first and third clutches C 1 and C 3 are operated.

In a skip up-shifting process from the fourth forward speed D 4 to the sixth forward speed D 6 , the second clutch C 2 is released and the first clutch C 1 is operated.

In a skip up-shifting process from the fifth forward speed D 5 to the seventh forward speed D 7 , the second clutch C 2 is released and the first brake B 1 is operated.

In a skip up-shifting process from the first forward speed D 1 to the fourth forward speed D 4 , the first and second brakes B 1 and B 2 are released and the second clutch C 2 and the third brake B 3 are operated.

In a skip up-shifting process from the second forward speed D 2 to the fifth forward speed D 5 , the second and third brakes B 2 and B 3 are released and the first and second clutches C 1 and C 2 are operated.

In a skip up-shifting process from the third forward speed D 3 to the sixth forward speed D 6 , the second clutch C 2 and the second brake B 2 are released and the first and third clutches C 1 and C 3 are operated.

In a skip up-shifting process from the fourth forward speed D 4 to the seventh forward speed D 7 , the second clutch C 2 and the third brake B 3 are released and the first clutch C 1 and the first brake B 1 are operated.

Skip down-shifting processes are reverse processes of the skip up-shifting processes according to an exemplary embodiment of the present invention.

As shown in FIG. 3 , an exemplary power train of an automatic transmission according to an embodiment of the present invention includes one compound planetary gear set and two single pinion planetary gear sets. In addition, the second ring gear R 2 is fixedly connected to the first planet carrier PC 1 , and the first sun gear S 1 is variably connected to the second sun gear S 2 via the third clutch C 3 . Therefore, operational elements of the exemplary power train of an automatic transmission according to the embodiment of the present invention are represented as eight nodes in the lever diagram.

Accordingly, the third sun gear S 3 is set to a first node N 1 , the short-pinion-side ring gear SR is set to a second node N 2 , the third planet carrier PC 3 is set to a third node N 3 , the long-pinion-side ring gear LR is set to a fourth node N 4 , the first ring gear R 1 is set to a fifth node N 5 , the second ring gear R 2 and the first planet carrier PC 1 are set to a sixth node N 6 , the second planet carrier PC 2 is set to a seventh node N 7 , and the first sun gear S 1 and the second sun gear S 2 are set to an eighth node N 8 .

As described above, the fourth node N 4 of the long-pinion-side ring gear LR always acts as the input element by being fixedly connected to the input shaft 100 .

The third planet carrier PC 3 is fixedly connected to the first ring gear R 1 . Therefore, the fifth node N 5 and the third node N 3 rotate with the same rotational speed.

The sixth node N 6 of the second ring gear R 2 is variably connected to the input shaft 100 via the first clutch C 1 . Therefore, rotational speed of the engine inputted through the input shaft 100 is transmitted to the sixth node N 6 by an operation of the first clutch C 1 .

The first planet carrier PC 1 is variably connected to the first sun gear S 1 via the second clutch C 2 . Therefore, the sixth node N 6 and the eighth node N 8 rotate with the same rotational speed, by an operation of the second clutch C 2 .

In addition, the short-pinion-side ring gear SR is variably connected to the transmission case 300 via the first brake B 1 , and at least one of the fixedly connected first sun gear S 1 and the second sun gear S 2 is variably connected to the transmission case 300 via the second brake B 2 . The third sun gear S 3 is variably connected to the transmission case 300 via the third brake B 3 , and the first planet carrier PC 1 is variably connected to the transmission case 300 via the fourth brake B 4 . Therefore, the second node N 2 , the eighth node N 8 , the first node N 1 , and the sixth node N 6 may be stopped by operations of the first, second, third, and fourth brakes B 1 , B 2 , B 3 , and B 4 , respectively.

Hereinafter, formation of each speed by the power-train of an automatic transmission according to the exemplary embodiment of the present invention will be described in detail, with reference to FIG. 3 .

In the first forward speed D 1 , the second node N 2 is stationary since the first brake B 1 is operated, and the fourth node N 4 rotates with the same rotational speed of the input shaft 100 . Therefore, the third node N 3 rotates with a first reduced rotational speed, and the fifth node N 5 fixedly connected to the third node N 3 rotates with the first reduced rotational speed. In addition, the eighth node N 8 is stationary since the second brake B 2 and the third clutch C 3 are operated. Therefore, the first forward speed D 1 is achieved at the seventh node N 7 that is the output element.

In the second forward speed D 2 , the first node N 1 is stationary since the third brake B 3 is operated, and the fourth node N 4 rotates with the same rotational speed of the input shaft 100 . Therefore, the third node N 3 rotates with a second reduced rotational speed, and the fifth node N 5 fixedly connected to the third node N 3 rotates with the second reduced rotational speed. In addition, the eighth node N 8 is stationary since the second brake B 2 and the third clutch C 3 are operated. Therefore, the second forward speed D 2 is achieved at the seventh node N 7 that is the output element.

In the third forward speed D 3 , the first node N 1 is stationary since the third brake B 3 is operated, and the fourth node N 4 rotates with the same rotational speed of the input shaft 100 . Therefore, the third node N 3 rotates with the second reduced rotational speed, and the fifth node N 5 fixedly connected to the third node N 3 rotates with the second reduced rotational speed. In addition, the sixth node N 6 rotates with the same rotational speed of the fifth node N 5 since the second clutch C 2 is operated, and the eighth node N 8 is stationary since the second brake B 2 is operated. Therefore, the first forward speed D 3 is achieved at the seventh node N 7 that is the output element.

In the fourth forward speed D 4 , the first node N 1 is stationary since the third brake B 3 is operated, and the fourth node N 4 rotates with the same rotational speed of the input shaft 100 . Therefore, the third node N 3 rotates with the second reduced rotational speed, and the fifth node N 5 fixedly connected to the third node N 3 rotates with the second reduced rotational speed. In addition, the sixth node N 6 and the eighth node N 8 respectively rotate with the same rotational speed of the fifth node N 5 since the second clutch C 2 and the third clutch C 3 are operated. Therefore, the first forward speed D 4 is achieved at the seventh node N 7 that is the output element.

In the fifth forward speed D 5 , the sixth node N 6 rotates with the same rotational speed of the input shaft 100 since the first clutch C 1 is operated. In addition, the fifth node N 5 and the eighth node N 8 respectively rotate with the same rotational speed of the sixth node N 6 since the second clutch C 2 and the third clutch C 3 are operated. Therefore, the first forward speed D 5 is achieved at the seventh node N 7 that is the output element.

In the sixth forward speed D 6 , the first node N 1 is stationary since the third brake B 3 is operated, and the fourth node N 4 rotates with the same rotational speed of the input shaft 100 . Therefore, the third node N 3 rotates with the second reduced rotational speed, and the fifth node N 5 fixedly connected to the third node N 3 rotates with the second reduced rotational speed. In addition, the sixth node N 6 rotates with the same rotational speed of the input shaft 100 since the first clutch C 1 is operated. Therefore, the first forward speed D 6 is achieved at the seventh node N 7 that is the output element.

In the seventh forward speed D 7 , the second node N 2 is stationary since the first brake B 1 is operated, and the fourth node N 4 rotates with the same rotational speed of the input shaft 100 . Therefore, the third node N 3 rotates with the first reduced rotational speed, and the fifth node N 5 fixedly connected to the third node N 3 rotates with the first reduced rotational speed. In addition, the sixth node N 6 rotates with the same rotational speed of the input shaft 100 since the first clutch C 1 is operated. Therefore, the first forward speed D 7 is achieved at the seventh node N 7 that is the output element.

In the first reverse speed REV. 1 , the second node N 2 is stationary since the first brake B 1 is operated, and the fourth node N 4 rotates with the same rotational speed of the input shaft 100 . Therefore, the third node N 3 rotates with the first reduced rotational speed, and the fifth node N 5 fixedly connected to the third node N 3 rotates with the first reduced rotational speed. In addition, the sixth node N 6 is stationary since the fourth brake B 4 is operated. Therefore, the first reverse speed REV. 1 is achieved at the seventh node N 7 that is the output element.

In the second reverse speed REV. 2 , the first node N 1 is stationary since the third brake B 3 is operated, and the fourth node N 4 rotates with the same rotational speed of the input shaft 100 . Therefore, the third node N 3 rotates with the second reduced rotational speed, and the fifth node N 5 fixedly connected to the third node N 3 rotates with the second reduced rotational speed. In addition, the sixth node N 6 is stationary since the fourth brake B 4 is operated. Therefore, the second reverse speed REV. 2 is achieved at the seventh node N 7 that is the output element.

As described above, the speed line for each planetary gear set may be easily obtained by a person of an ordinary skill in the art based on the teachings herein.

According to an exemplary embodiment of the present invention, the seven forward speeds and two reverse speeds may be realized by utilizing three planetary gear sets, three clutches, and four brakes.

In addition, shift feel may be improved by reducing frictional elements that are engaged or released in the shifting processes.

While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.