Abstract:
A six-speed power train of an automatic transmission for a vehicle includes: a first, double pinion planetary gear set including a first operational element always operating as an input element, a second operational element selectively operating as an output and a fixed element, and a third operational element selectively operating as an input element, an output element, and a fixed element; a second, Ravingneaux type planetary gear set including a first operational element selectively operating as an input element, a second operational element always operating as an output element, a third operational element selectively operating as an input element and a fixed element, and a fourth operational element selectively operating as a fixed element; a plurality of clutches disposed between and variably connecting operational elements of the first and second planetary gear sets; and a plurality of brakes variably connecting a transmission housing with one of the fixed elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2006-0065034 filed in the Korean Intellectual Property Office on Jul. 11, 2006, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to an automatic transmission, and more particularly, to a power train of an automatic transmission. 
         [0004]    (b) Description of the Related Art 
         [0005]    A multi-stage gearshift mechanism of an automatic transmission includes a plurality of planetary gear sets. A power train having such a plurality of planetary gear sets varies the torque in multiple stages and outputs it to an output shaft when receiving a converted engine torque from a torque converter. 
         [0006]    The more speeds the power train of an automatic transmission has, the better the power performance and fuel consumption. Therefore, it is desirable for power trains to have as many speeds as possible. 
         [0007]    For the same number of speeds, durability, power transmission efficiency, and size/weight of a transmission are substantially dependent on how the planetary gear sets are arranged. 
         [0008]    For a manual transmission, too many speeds cause a driver the inconvenience of excessive manual shifting. However, for an automatic transmission, a transmission control unit automatically executes shifting by controlling the operation of the power train, and therefore, more speeds usually implies more merits. 
         [0009]    Accordingly, recently, a power train of an automatic transmission enabling six forward speeds and one reverse speed has been developed. 
         [0010]    However, according to the conventional power train, because the clutches and the brakes are disposed to a back of the transmission, an operating hydraulic line is difficult to be formed. 
         [0011]    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. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides a power train of an automatic transmission having advantages of effectively forming a hydraulic line, minimizing a power loss, and improving drivability. 
         [0013]    In addition, the present invention has suppresses tire slip by lowering a first forward speed gear ratio and improves high speed driving performance and reverse running performance. 
         [0014]    An exemplary embodiment of the present invention provides a six-speed power train of an automatic transmission for a vehicle including: a first, double pinion planetary gear set including a first operational element always operating as an input element, a second operational element selectively operating as an output element and a fixed element, and a third operational element selectively operating as an input, an output, and a fixed element; a second, Ravingneaux type planetary gear set including a first operational element selectively operating as an input element, a second operational element always operating as an output element, a third operational element selectively operating as an input and a fixed element, and a fourth operational element selectively operating a fixed element; a plurality of clutches disposed between operational elements of the first and second planetary gear sets and variably connecting corresponding operational elements; and a plurality of brakes variably connecting a transmission housing with an operational element operating as the fixed element. 
         [0015]    The first operational element of the first planetary gear set is a first sun gear, the second operational element is a first ring gear, and the third operational element is a first planet carrier. 
         [0016]    The first operational element of the second planetary gear set may be a second sun gear engaged with a short pinion, the second operational element is a second ring gear, the third operational element is a second planet carrier, and the fourth operational element is a third sun gear engaged with a long pinion. 
         [0017]    The first operational element of the first planetary gear set is fixedly connected to the input shaft, the second operational element of the first planetary gear set is variably connected to the second operational element of the second planetary gear set and also variably connected to a transmission housing, the third operational element of the first planetary gear set is variably connected to the input shaft and also variably connected to the transmission housing and fixedly connected to the third operational element of the second planetary gear set. 
         [0018]    The first operational element of the second planetary gear set is variably connected to the first operational element of the first planetary gear set, the second operational element of the second planetary gear set is variably connected to the second operational element of the first planetary gear set and also connected to the output gear, the third operational element of the second planetary gear set is fixedly connected to the third operational element of the first planetary gear set, and the fourth operational element of the second planetary gear set is variably connected to the transmission housing. 
         [0019]    The plurality of clutches includes a first clutch disposed between the first operational element and the third operational element of the first planetary gear set, a second clutch disposed between the first operational element of the first planetary gear set and the first operational element of the second planetary gear set, and a third clutch disposed between the second operational element of the first planetary gear set and the second operational element of the second planetary gear set. 
         [0020]    The plurality of brakes includes a first brake disposed between the third operational element of the first planetary gear set and the transmission housing, a second brake disposed between the second operational element of the first planetary gear set and the transmission housing, and a third brake disposed between the fourth operational element of the second planetary gear set and the transmission housing. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic diagram of a power train according to an exemplary embodiment of the present invention; 
           [0022]      FIG. 2  shows a basic scheme of a power train according to an exemplary embodiment of the present invention; 
           [0023]      FIG. 3  is a shift diagram of first, third, and fifth forward speeds and a first reverse speed according to an exemplary embodiment of the present invention; 
           [0024]      FIG. 4  is a shift diagram of second and fourth forward speeds according to an exemplary embodiment of the present invention; 
           [0025]      FIG. 5  is a shift diagram of a sixth forward speed and a second reverse speed according to an exemplary embodiment of the present invention; and 
           [0026]      FIG. 6  is an operational chart according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Exemplary embodiments of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
         [0028]    Referring to  FIG. 1 , in an exemplary embodiment of the present invention, a power train includes first and second planetary gear sets PG 1  and PG 2  that are disposed to the same shaft, three clutches C 1 , C 2 , and C 3 , and three brakes B 1 , B 2 , and B 3 . 
         [0029]    The first planetary gear set PG 1  is a double pinion planetary gear set. 
         [0030]    The second planetary gear set PG 2  is a Ravingneaux type compound planetary gear set combining a single pinion planetary gear set with a double pinion planetary gear set to join a ring gear and a planet carrier. 
         [0031]    The first planetary gear set PG 1  includes a first sun gear S 1  operated as a first operational element, a first ring gear R 1  operated as a second operational element, and a first planet carrier PC 1  operated as a third operational element. 
         [0032]    The second planetary gear set PG 2  includes a second sun gear S 2  engaged with a short pinion P 1  and operating as a first operational element, a second ring gear R 2  operating as a second operational element, a second planet carrier PC 2  supporting the short pinion P 1  and a long pinion P 2  and operating as a third operational element, and a third sun gear S 3  engaged with the long pinion P 2  and operating as a fourth operational element. 
         [0033]    The first sun gear S 1  and the input shaft IS are fixedly connected with each other such that the first sun gear S 1  always acts as an input element. The first planet carrier PC 1  and the second planet carrier PC 2  are fixedly connected with each other. 
         [0034]    The first clutch C 1  is disposed between the first sun gear S 1  and the first planet carrier PC 1 , and the first clutch C 1  variably connects the input shaft and the first planet carrier PC 1 . 
         [0035]    The second clutch C 2  is disposed between the first sun gear S 1  and the second sun gear S 2 . 
         [0036]    The third clutch C 3  is disposed between and variably connects the first ring gear R 1  and the second ring gear R 2 . 
         [0037]    The first planet carrier PC 1  and the first ring gear R 1  are variably connected to the transmission housing H via the first and second brakes B 1  and B 2 , respectively. 
         [0038]    The third sun gear S 3  is variably connected to the transmission housing H via the third brake B 3 . 
         [0039]    An output gear OG is connected to the second ring gear R 2  to always operate as an output element. 
         [0040]    The output gear OG transmits power to a differential apparatus via a final reducing gear by any known scheme. 
         [0041]    According to an exemplary embodiment of the present invention, as shown in  FIG. 2 , the first planetary gear set PG 1  is shown on a lever and the first operational element A is the first sun gear S 1 , the second operational element B is the first ring gear R 1 , and the third operational element C is the first planet carrier PC 1 . 
         [0042]    The second planetary gear set PG 2  is shown on a lever in  FIG. 2  where the first operational element D is the second sun gear S 2 , the second operational element E is the second ring gear R 2 , the third operational element F is the second planet carrier PC 2 , and the fourth operational element G is the third sun gear S 3 . 
         [0043]    The third operational element C of the first planetary gear set PG 1  and the third operational element F of the second planetary gear set PG 2  are fixedly connected. 
         [0044]    The first operational element A of the first planetary gear set PG 1  is variably connected to the first operational element D of the second planetary gear set PG 2  via the second clutch C 2 . 
         [0045]    The second operational element B of the first planetary gear set PG 1  is variably connected to the second operational element E of the second planetary gear set PG 2  via the third clutch C 3 . 
         [0046]    Therefore, if the first operational element A of the first planetary gear set PG 1  is connected to the first operational element D of the second planetary gear set PG 2  via the second clutch C 2 , five operational nodes N 1 , N 2 , N 3 , N 4 , and N 5  are determined on the lever, as shown in  FIG. 3 . 
         [0047]    That is, the first operational node N 1  is the first operational element A of the first planetary gear set PG 1  and the first operational element D of the second planetary gear set PG 2 , the second operational node N 2  is the second operational element B of the first planetary gear set PG 1 , the third operational node N 3  is the second operational element E of the second planetary gear set PG 2 , the fourth operational node N 4  is the third operational element C of the first planetary gear set PG 1  and the third operational element F of the second planetary gear set PG 2 , and the fifth operational node N 5  is the fourth operational element G of the second planetary gear set PG 2 . 
         [0048]    In addition, if the second operational element B of the first planetary gear set PG 1  is connected to the second operational element E of the second planetary gear set PG 2  via the third clutch C 3 , five operational nodes N 1 , N 2 , N 3 , N 4 , and N 5  are determined on the lever, as shown in  FIG. 4 . 
         [0049]    That is, the first operational node N 1  is the first operational element D of the second planetary gear set PG 2 , the second operational node N 2  is the first operational element A of the first planetary gear set PG 1 , the third operational node N 3  is the second operational element B of the first planetary gear set PG 1  and the second operational element E of the second planetary gear set PG 2 , the fourth operational node N 4  is the third operational element C of the first planetary gear set PG 1  and the third operational element F of the second planetary gear set PG 2 , and the fifth operational node N 5  is the fourth operational element G of the second planetary gear set PG 2 . 
         [0050]    In addition, if the second and third clutches C 2  and C 3  do not operate, six operational nodes N 1 , N 2 , N 3 , N 4 , N 5 , and N 6  are determined on the lever, as shown in  FIG. 5 . 
         [0051]    That is, the first operational node N 1  is the first operational element D of the second planetary gear set PG 2 , the second operational node N 2  is the first operational element A of the first planetary gear set PG 1 , the third operational node N 3  is the second operational element E of the second planetary gear set PG 2 , the fourth operational node N 4  is the second operational element B of the first planetary gear set PG 1 , the fifth operational node N 5  is the third operational element C of the first planetary gear set PG 1  and the third operational element F of the second planetary gear set PG 2 , and the sixth operational node N 6  is the fourth operational element G of the second planetary gear set PG 2 . 
         [0052]    The method for determining operational nodes will be understood by persons of an ordinary skill in the art based on the teachings herein, and so a detailed description thereof is omitted. 
         [0053]    According to an exemplary embodiment of the present invention, the power train is shifted by controlling frictional elements as shown in  FIG. 6 , and the shifting process is as follows, referring to  FIGS. 3 ,  4 , and  5 . 
         [0054]    For the first forward speed, the first brake B 1  and the second clutch C 2  are operated. 
         [0055]    Because the second clutch C 2  is operated, as shown in  FIG. 3 , the respective third operational elements C and F of the first and second planetary gear sets PG 1  and PG 2 , which are the fifth operational node N 5 , are operated as a fixed element by operation of the second brake B 2  while the respective first operational elements A and D of the first and second planetary gear sets PG 1  and PG 2 , which are the first operational node N 1 , remain receiving an input from an engine. 
         [0056]    Therefore, the first forward speed line SP 1  is attained by operation of the first and second planetary gear sets PG 1  and PG 2 , which are fixedly connected, as shown in  FIG. 3 . 
         [0057]    The output element of the second operational element E of the second planetary gear set PG 2 , which is the third operational node N 3 , rotates at a speed D 1 , and the first forward speed is attained. 
         [0058]    To shift from the first to the second forward speed, the second clutch C 2  is released and the third clutch C 3  is operated. 
         [0059]    Because the third clutch C 3  is operated, as shown in  FIG. 4 , the first operational element A of the first planetary gear set PG 1 , which is the second operational node N 2 , receives the input of the engine. 
         [0060]    In addition, the fourth operational node N 4  is operated as the fixed element by the operation of the first brake B 1 , as in the first forward speed. 
         [0061]    Therefore, the second forward speed line SP 2  is formed. 
         [0062]    The output element of the second operational element B of the first planetary gear set PG 1  and the second operational element E of the second planetary gear set PG 2 , which are the third operational node N 3 , rotate at a speed D 2  and the second forward speed is realized. 
         [0063]    To shift from the second to the third forward speed, the first brake B 1  and the third clutch C 3  are released and the third brake B 3  and the second clutch C 2  are operated. 
         [0064]    Because the second clutch C 2  is operated, as shown in  FIG. 3 , the fifth operational node N 5  is operated as the fixed element while the first operational node N 1  remains receiving the input of the engine. 
         [0065]    Therefore, the third forward speed line SP 3  is formed and an output element of the second operational element E of the second planetary gear set PG 2 , which is the third operational node N 3 , rotates at a speed D 3  and the third forward speed is realized. 
         [0066]    To shift from the third to the fourth forward speed, the second clutch C 2  is released and the third clutch C 3  is operated. 
         [0067]    Because the third clutch C 3  is operated, as shown in  FIG. 4 , the first operational element A of the first planetary gear set PG 1 , which is the second operational node N 2 , receives the input. 
         [0068]    In addition, the fifth operational node N 5  is operated as the fixed element by an operation of the third brake B 3 . 
         [0069]    Therefore, the fourth forward speed line SP 4  is formed and an output element of the second operational element B of the first planetary gear set PG 2  and the second operational element E of the second planetary gear set PG 2 , which are the third operational node N 3 , rotate at a speed D 4  and the fourth forward speed is realized. 
         [0070]    To shift from the fourth to the fifth forward speed, the third brake B 3  is released and the first clutch C 1  is operated. 
         [0071]    The first operational element A and the third operational element C of the second planetary gear set PG 2  receive two inputs from the engine by an operation of the third clutch C 3 , while the first planetary gear set PG 1  receives the engine speed at the same time by an operation of the first clutch C 1 . 
         [0072]    Therefore, the second planetary gear set PG 2  receives two inputs of the engine speed at the same time as shown in  FIG. 4 , the fifth forward speed line SP 5  is formed, an output element rotates at a speed D 5  (i.e., at the same speed as the input engine speed), and the fifth forward speed is realized. 
         [0073]    To shift from the fifth to the sixth forward speed, the third clutch C 3  is released and the third brake B 3  is operated. 
         [0074]    The second and third clutches C 2  and C 3  are not operated, and the shifting is realized as shown in  FIG. 5 . 
         [0075]    Because the first planetary gear set PG 2  receives two inputs of the engine speed at the same time by the operation of the first clutch C 1 , the fourth operational element G of the second planetary gear set PG 2 , which is the sixth operational node N 6 , is operated as the fixed element by the operation of the third brake B 3 , while the fifth operational node N 5  remains receiving the input of the engine speed. 
         [0076]    Therefore, the sixth forward speed line SP 6  is formed and an output element of the third operational node N 3  rotates as a speed D 6  faster than the input engine speed and the sixth forward speed is realized. 
         [0077]    For the first reverse speed, the second clutch C 2  and the second brake B 2  are operated. 
         [0078]    And then, shifting is realized, as shown in  FIG. 3 , by the operation of the second clutch C 2 . 
         [0079]    At that time, the second operational element B of the first planetary gear set PG 1 , which is the second operational node N 2 , is operated as the fixed element by the second brake B 2 , while the first operational node N 1  remains receiving the input of the engine speed. 
         [0080]    Therefore, a first reverse speed line SR 1  is formed and an output element of the third operational node N 3  rotates at a speed rs 1  and the first reverse speed is realized. 
         [0081]    To shift from the first to the second reverse speed, the second clutch C 2  is released and the third brake B 3  is operated. 
         [0082]    Because the second and third clutches C 2  and C 3  are not operated, as shown in  FIG. 5 , the shifting is realized. 
         [0083]    The second operational element B of the first planetary gear set PG 2 , which is the fourth operational node N 4 , is operated as the fixed element, while the first operational element A of the first planetary gear set PG 1 , which is the second operational node N 2 , remains receiving the input of the engine speed by the operation of the second brake B 2 . 
         [0084]    Therefore, a first second reverse speed line SR 2  is formed, and the fifth operational node N 5  is reversed and the second planetary gear set PG 2  receives the input of the engine speed. 
         [0085]    In this state, a second reverse speed line SR 21  is formed by the operation of the third brake B 3 , and an output element of the third operational node N 3  rotates at a speed rs 2  and the second reverse speed is attained. 
         [0086]    According to an exemplary embodiment of the present invention, if the number of teeth of the first sun gear S 1  and the first ring gear R 1  are 35 and 80, and of the second sun gear S 2 , the third sun gear S 3 , and the second ring gear R 2  are respectively 30, 40, and 100, step ratios of the respective speed ratios can be optimized by which the speed ratios are 3.333 in the first forward speed, 2.286 in the second forward speed, 1.667 in the third forward speed, 1.367 in the fourth forward speed, 1.000 in the fifth forward speed, and 0.714 in the sixth forward speed, as shown in  FIG. 6 . 
         [0087]    As described, according to an exemplary embodiment of the present invention, hydraulic lines can be easily formed by disposing the brakes and the clutches dispersedly, and drivability can be improved by optimizing step ratios. 
         [0088]    Also, as shown in the speed diagram, because slip speeds of the revolving frictional elements are small, power loss can be minimized. 
         [0089]    In addition, tire slip is minimized when a vehicle starts by lowering the first forward speed ratio, high speed driving performance can be improved by the speed being faster than the input engine speed from the fifth forward speed, and reverse running performance can be improved by forming two reverse speeds. 
         [0090]    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.