Abstract:
The powertrain includes an arrangement of three single planetary gearsets of which operational elements are wisely interconnected to one another via two clutches and to the transmission via three brakes so as to form six forward speeds and one reverse speed, to be adaptable to a rear wheel drive vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0013084 filed in the Korean Intellectual Property Office on Feb. 26, 2004, the entire content of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     Generally, the present invention relates to a powertrain of an automatic transmission for a rear wheel drive vehicle enabling six forward speeds.  
       BACKGROUND OF THE INVENTION  
       [0003]     A multi-stage gearshift mechanism of an automatic transmission includes a plurality of planetary gearsets. A powertrain having such a plurality of planetary gearsets varies the torque in multi-stages and outputs it to an output shaft when receiving a converted engine torque from a torque converter. The more speeds the powertrain of an automatic transmission has, the better power performance and fuel consumption. Therefore, it is desirable to have as many speeds as possible in powertrains.  
         [0004]     Even for the same number of speeds, durability, power transmission efficiency, and size/weight of a transmission are substantially dependent on how planetary gearsets are arranged. Therefore, research for more structural strength, less power loss, and more compact packaging are under continuing investigation.  
         [0005]     Usually, development of a powertrain using planetary gearsets does not devise wholly new type of planetary gearsets. To the contrary, it invokes how single/double pinion planetary gearsets are combined, and how clutches, brakes, and one-way clutches are disposed to the combination of planetary gearsets such that required shift speeds and speed ratios are realized with minimal power loss.  
         [0006]     As 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.  
         [0007]     Accordingly, research of four-speed and five-speed powertrains has been undertaken, and recently, a powertrain of an automatic transmission enabling six forward speeds and one reverse speed has been developed. Such six forward speed powertrains often include a Lavingneaux planetary gearset in the rear and a single pinion planetary gearset in the front.  
         [0008]     A Lavingneaux type planetary gearset usually has drawbacks in consumption of volume and weight. Therefore, such powertrains for a rear wheel drive vehicle using a Lavingneaux type planetary gearset together with a single pinion planetary gearset results in inferiority in production efficiency. Furthermore, such Lavingneaux type planetary gearsets show inferior durability in comparison with single pinion planetary gearsets.  
         [0009]     The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known in this country to a person of ordinary skill in the art.  
       SUMMARY  
       [0010]     The present invention has been made in an effort to provide a powertrain of an automatic transmission for a rear wheel drive vehicle having advantages of small volume, light weight, durability, and production efficiency.  
         [0011]     An exemplary six-speed powertrain of an automatic transmission for a rear wheel drive vehicle according to an embodiment of the present invention includes: a first planetary gearset of a single pinion planetary gearset having a first sun gear, a first planet carrier, and a first ring gear; a second planetary gearset of a single pinion planetary gearset having a second sun gear, a second planet carrier, and a second ring gear; and a third planetary gearset of a single pinion planetary gearset having a third sun gear, a third planet carrier, and a third ring gear.  
         [0012]     In the previously mentioned powertrain, the first ring gear and the second planet carrier, the second ring gear and the third planet carrier, and the third ring gear and the first planet carrier are fixedly interconnected respectively. The second sun gear is fixedly connected to an input shaft so as to always act as an input element. The third sun gear is variably connected to the input shaft and the transmission case interposing a first clutch and a third brake respectively. The second planet carrier is variably connected to the input shaft interposing a second clutch. The third planet carrier is variably connected to the transmission case interposing a second brake and a one-way clutch. The first planet carrier is connected to an output gear. The first sun gear is variably connected to the transmission housing interposing a first brake.  
         [0013]     In a further embodiment, the first and second clutches and the second and third brakes are disposed to the front in the transmission case, and the first brake is disposed to the rear in the transmission case.  
         [0014]     In another further embodiment, the one-way clutch and the second brake are connected to the third planet carrier in parallel.  
         [0015]     In another further embodiment, the output gear is disposed opposite to the input shaft with respect to the first, second, and third planetary gearsets 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The accompanying drawings illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention, wherein:  
         [0017]      FIG. 1  is a schematic diagram of a powertrain according to an embodiment of the present invention;  
         [0018]      FIG. 2  is an operational chart for a powertrain according to an embodiment of the present invention;  
         [0019]      FIG. 3  shows lever diagrams for first and second forward speeds of a powertrain according to an embodiment of the present invention;  
         [0020]      FIG. 4  shows lever diagrams for third, fourth, and fifth forward speeds of a powertrain according to an embodiment of the present invention; and  
         [0021]      FIG. 5  shows lever diagrams for a sixth forward speed and a reverse speed of a powertrain according to an embodiment of the present invention;  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0022]     An embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings.  
         [0023]      FIG. 1  is a schematic diagram of a powertrain according to an embodiment of the present invention. The powertrain has a combination of first, second, and third planetary gearsets PG 1 , PG 2 , and PG 3  on an input shaft  2  connected to an engine via a torque converter. The first planetary gearset PG 1  is a single pinion planetary gearset having a first sun gear S 1 , a first ring gear R 1 , and a first planet carrier PC 1  rotatably supporting first planetary gears P 1  engaged with the first sun gear S 1  and the first ring gear R 1  therebetween.  
         [0024]     The second planetary gearset PG 2  is a single pinion planetary gearset having a second sun gear S 2 , a second ring gear R 2 , and a second planet carrier PC 2  rotatably supporting second planetary gears P 2  engaged with the second sun gear S 2  and the second ring gear R 2  therebetween. The third planetary gearset PG 3  is a single pinion planetary gearset having a third sun gear S 3 , a third ring gear R 3 , and a third planet carrier PC 3  rotatably supporting third planetary gears P 3  engaged with the third sun gear S 3  and the third ring gear R 3  therebetween.  
         [0025]     The first, second, and third planetary gearsets PG 1 , PG 2 , and PG 3  are arranged in an order of the first, second, and third planetary gearsets PG 1 , PG 2 , and PG 3  from a rear of the transmission. Among the operational elements, the first ring gear R 1  and the second planet carrier PC 2 , the second ring gear R 2  and the third planet carrier PC 3 , and the first planet carrier PC 1  and the third ring gear R 3  are fixedly interconnected, respectively.  
         [0026]     The second sun gear S 2  is fixedly connected to the input shaft  2  so as to always act as an input element. The third sun gear S 3  and the second planet carrier PC 2  are variably connected to the input shaft  2  interposing first and second clutches C 1  and C 2 , respectively, and they respectively act as variable input elements.  
         [0027]     In addition, the first sun gear S 1  is variably connected to a transmission case  4  interposing a first brake B 1 . The third planet carrier PC 3  is variably connected to the transmission case  4  interposing a second brake B 2  and a one-way clutch OWC in parallel, so as to variably act as stationary elements. The third sun gear S 3  is connected to the transmission case  4  interposing the third brake B 3 . The first planet carrier PC 1  always acts as an output element.  
         [0028]     In addition, the first and second clutches C 1  and C 2  and the second and third brakes B 2  and B 3  are disposed to the front (i.e., toward the input shaft) in the transmission case, and the first brake B 1  is disposed to the rear (i.e., opposite to the input shaft) in the transmission case.  
         [0029]     Such a powertrain is operated according to an operational chart of  FIG. 2  so as to form six forward speeds and one reverse speed. That is, the first brake B 1  and the one-way clutch OWC operate in the first forward speed, the first and third brakes B 1  and B 3  operate in the second forward speed, the first clutch C 1  and the first brake B 1  operate in the third forward speed, the second clutch C 2  and the first brake B 1  operate in the fourth forward speed, the first and second clutches C 1  and C 2  operate in the fifth forward speed, the second clutch C 2  and the third brake B 3  operate in the sixth forward speed, and first clutch C 1  and the second brake B 2  operate in the reverse speed. Regarding the first forward speed, the second brake B 2  may be operated instead of the one-way clutch OWC for realizing an engine brake, so the operation of second brake B 2  in the first speed is marked with an empty circle in  FIG. 2 .  
         [0030]     Such a powertrain according to an embodiment of the present invention uses a combination of three single pinion planetary gearsets wherein the first ring gear R 1  and the second planet carrier PC 2 , the second ring gear R 2  and the third planet carrier PC 3 , the third ring gear R 3  and the first planet carrier PC 1  are fixedly interconnected respectively. Therefore, the operational elements may be understood to have 6 nodes as shown in  FIG. 3 .  
         [0031]     In more detail, the second sun gear S 2  corresponds to a first node N 1 , the third sun gear S 3  corresponds to a second node N 2 , the first ring gear R 1  and the second planet carrier PC 2  correspond to a third node N 3 , the second ring gear R 2  and the third planet carrier PC 3  correspond to a fourth node N 4 , the first planet carrier PC 1  and the third ring gear R 3  correspond to a fifth node N 5 , and the first sun gear S 1  corresponds to a sixth node N 6 , respectively.  
         [0032]      FIGS. 3-5  are lever diagrams visualizing shifting of a powertrain according to an embodiment of the present invention. At the first forward speed, the first brake B 1  and the one-way clutch OWC operate. Then, the fourth node N 4  and the sixth node N 6  act as stationary elements while the second sun gear S 2  of the first node N 1  receives input torque. Therefore, according to a cooperative reaction of the first, second, and third planetary gearsets PG 1 , PG 2 , and PG 3 , the speed diagram becomes as shown in a first speed diagram in  FIG. 3 . Therefore, shifting to the forward first speed is realized because speed is changed to and output as D 1  through the output element of the fifth node N 5 .  
         [0033]     At the second forward speed, the third brake B 3  operates instead of the one way clutch OWC (or the second brake B 2 ) in the first speed. Then, the second node N 2  and the sixth node N 6  act as stationary elements, while the second sun gear S 2  of the first node N 1  receives input torque. Therefore, according to a cooperative reaction of the first, second, and third planetary gearsets PG 1 , PG 2 , and PG 3 , the speed diagram becomes as shown in a second speed diagram in  FIG. 3 . Therefore, shifting to the forward second speed is realized because speed is changed to and output as D 2  through the output element of the fifth node N 5 .  
         [0034]     At the third forward speed, the third brake B 3  is released and the first clutch C 1  operates, in comparison with the second forward speed. Then, the sixth node N 6  acts as a stationary element, while the second sun gear S 2  of the first node N 1  and the third sun gear S 3  of the second node N 2  receive input torque. Therefore, according to a cooperative reaction of the first, second, and third planetary gearsets PG 1 , PG 2 , and PG 3 , the speed diagram becomes as shown in a third speed diagram in  FIG. 4 . Therefore, shifting to the forward third speed is realized because speed is changed to and output as D 3  through the output element of the fifth node N 5 .  
         [0035]     At the fourth forward speed, the first clutch C 1  is released and the second clutch C 2  operates, in comparison with the third speed. Then, the sixth node N 6  acts as a stationary element while second sun gear S 2  of the first node N 1  and the second carrier PC 2  of the third node N 3  receive input torque. Therefore, according to a cooperative reaction of the first, second, and third planetary gearsets PG 1 , PG 2 , and PG 3 , the speed diagram becomes as shown in a fourth speed diagram in  FIG. 4 . Therefore, shifting to the forward fourth speed is realized because speed is changed to and output as D 4  through the output element of the fifth node N 5 .  
         [0036]     At the fifth forward speed, the first brake B 1  is released and the first clutch C 1  operates, in comparison with the fourth speed. Then, no stationary element is formed while the second sun gear S 2  of the first node N 1  and the third sun gear S 3  of the second node N 2  receive input torque. Therefore in this case, the first, second, and third planetary gearsets PG 1 , PG 2 , and PG 3  integrally rotate. Therefore, shifting to the fifth forward speed is realized because the speed is changed to and output as D 5  through the output element of the fifth node N 5  as shown in the fifth speed diagram in  FIG. 4 .  
         [0037]     At the sixth forward speed, the first clutch C 1  is released and the third brake B 3  operates, in comparison with the fifth speed. Then, the second node N 2  acts as a stationary element while the second sun gear S 2  of the first node N 1  and the second carrier PC 2  of the third node N 3  receive input torque. Therefore, according to a cooperative reaction of the first, second, and third planetary gearsets PG 1 , PG 2 , and PG 3 , the speed diagram becomes as shown in a sixth speed diagram in  FIG. 5 . Therefore, shifting to the forward sixth speed is realized because speed is changed to and output as D 6  through the output element of the fifth node N 5 .  
         [0038]     At the reverse speed, the first clutch C 1  and the second brake B 2  operate. Then, the fourth node N 4  acts as a stationary element while the second sun gear S 2  of the first node N 1  and the third sun gear S 3  of the second node N 2  receive input torque. Therefore, according to a cooperative reaction of the first, second, and third planetary gearsets PG 1 , PG 2 , and PG 3 , the speed diagram becomes as shown in a reverse speed diagram in  FIG. 5 . Therefore, shifting to the reverse speed is realized because speed is changed to and output as R through the output element of the fifth node N 5 . Details of drawing speed diagrams for each planetary gearset at each speed are obvious from the above description, and are not described in further detail.  
         [0039]     A powertrain according to an embodiment of the present invention shows speed ratios of 4.793 at the first forward speed, 2.796 at the second forward speed, 1.776 at the third forward speed, 1.342 at the fourth forward speed, 1.000 at the fifth forward speed, and 0.777 at the sixth forward speed. Accordingly, step ratios of speed ratios at each speed are optimally formed.  
         [0040]     According to a powertrain according to an embodiment of the present invention, single pinion planetary gearsets which generally occupy less volume and show less weight are dominantly used. Therefore, durability and production efficiency of a transmission are enhanced due to obviation of necessity of using a Lavingneaux type planetary gearset.  
         [0041]     In addition, all the clutches are disposed to the front, and accordingly, hydraulic paths thereto may be shortened. Usage of the one way clutch enhances responsiveness in shifting.  
         [0042]     While this invention has been described in connection with what is presently considered to be the most 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.