Abstract:
A gear train of an automatic transmission for a vehicle may be provided to realize eight forward speeds and one reverse speed with three single pinion planetary gear set, four clutches and two brakes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This present application claims priority to Korean Patent Application Number 10-2008-0051752 filed on Jun. 2, 2008, the entire contents of which are incorporated herein for all purposes by this reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a gear train of an automatic transmission for a vehicle which may realize eight forward speeds and one reverse speed with three single pinion planetary gear set, four clutches and two brakes. 
         [0004]    2. Description of Related Art 
         [0005]    A typical shift mechanism of an automatic transmission utilizes a combination of a plurality of planetary gear sets. A gear train of such an automatic transmission changes rotating speed and torque received from a torque converter of the automatic transmission and transmits the changed torque to an output shaft. 
         [0006]    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. 
         [0007]    In addition, with the same number of speeds, features of a gear train such as durability, efficiency in power transmission, and size depend a lot on the layout of combined planetary gear sets. Therefore, designs for a combining structure of a gear train are also under constant investigation. 
         [0008]    A manual transmission that has too many speeds causes 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 basically without needing manual operation. 
         [0009]    The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    Various aspects of the present invention are directed to provide a gear train of an automatic transmission for a vehicle which may realize eight forward speeds and one reverse speed with three single pinion planetary gear set, four clutches and two brakes. 
         [0011]    A gear train of an automatic transmission for a vehicle according to a first exemplary embodiment of the present invention may include: a first planetary gear set provided with three operating members, wherein a first operating member is selectively connected to an input shaft and selectively connected to a transmission case, a second operating member is selectively connected to the transmission case and a third operating member is fixedly connected to an output shaft; a second planetary gear set provided with three operating members, wherein a fourth operating member is fixedly connected to the input shaft, a fifth operating member, and a sixth operating member is fixedly connected with the second operating member; a third planetary gear set provided with three operating members, wherein a seventh operating member is fixedly connected to the transmission case, an eighth operating member is selectively connected to the input shaft and selectively connected with the third operating member, and a ninth operating member is fixedly connected with the fifth operating member; and a plurality of friction members comprising clutches and brakes that selectively connect the operating member with one of the other operating members, the transmission housing, or the input shaft, wherein two operating members of the first, second, and third operating members are selectively connected. 
         [0012]    The first operating member and the second operating member may be selectively connected. 
         [0013]    The plurality of friction members may include a first clutch selectively connects the eighth operating member to the input shaft, a second clutch selectively connects the first operating member to the input shaft, a third clutch selectively connects the first operating member with the second operating member, a fourth clutch selectively connects the third operating member with the eighth operating member, a first brake selectively connects the second operating member to the transmission case and a second brake selectively connects the first operating member to the transmission case. 
         [0014]    The first planetary gear set may be a single pinion planetary gear set comprising a first sun gear, a first planet carrier and a first ring gear, and the first sun gear is operated as the first operating member, the first planet carrier is operated as the second operating member and the first ring gear is operated as the third operating member, the second planetary gear set may be a single pinion planetary gear set comprising a second sun gear, a second planet carrier and a second ring gear, and the second sun gear is operated as the fourth operating member, the second planet carrier is operated as the fifth operating member and the second ring gear is operated as the sixth operating member, and the third planetary gear set may be a single pinion planetary gear set comprising a third sun gear, a third planet carrier and a third ring gear, and the third sun gear is operated as the seventh operating member, the third planet carrier is operated as the eighth operating member and the third ring gear is operated as the ninth operating member. 
         [0015]    The fourth clutch and the first brake may be operated in a first forward speed, the fourth clutch and the second brake may be operated in a second forward speed, the third clutch and the fourth clutch may be operated in a third forward speed, the second clutch and the fourth clutch may be operated in a fourth forward speed, the first clutch and the third clutch may be operated in a sixth forward speed, the first clutch and the second clutch may be operated in a seventh forward speed, the first clutch and the second brake may be operated in an eighth forward speed, the second clutch and the first brake may be operated in one reverse speed and one of a group including the second clutch and the third clutch and a group including the first clutch and the fourth clutch is operated in a fifth forward speed. 
         [0016]    A one-way clutch may be disposed in parallel with the first brake, the fourth clutch and the one-way clutch may be operated in a first forward speed, the fourth clutch and the second brake may be operated in a second forward speed, the third clutch and the fourth clutch may be operated in a third forward speed, the second clutch and the fourth clutch may be operated in a fourth forward speed, the first clutch and the third clutch may be operated in a sixth forward speed, the first clutch and the second clutch may be operated in a seventh forward speed, the first clutch and the second brake may be operated in an eighth forward speed, the second clutch and the first brake may be operated in one reverse speed and one of a group including the second clutch and the third clutch and a group including the first clutch and the fourth clutch is operated in a fifth forward speed. 
         [0017]    The second operating member and the third operating member according to a second exemplary embodiment of the present invention may be selectively connected. 
         [0018]    The plurality of friction members may includes a first clutch selectively connects the eighth operating member to the input shaft, a second clutch selectively connects the first operating member to the input shaft, a the third clutch selectively connects the second operating member with the third operating member, a fourth clutch selectively connects the third operating member with the eighth operating member, a first brake selectively connects the second operating member to the transmission case and a second brake selectively connects the first operating member to the transmission case. 
         [0019]    The gear train of an automatic transmission for a vehicle according to exemplary embodiments of the present invention may enhance power delivery performance with increased shift-speed and fuel consumption may be reduced. 
         [0020]    The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic diagram of an exemplary gear train according to the present invention. 
           [0022]      FIG. 2  is an operational chart for the gear train of  FIG. 1 . 
           [0023]      FIG. 3  to  FIG. 11  are lever diagrams of the gear train of  FIG. 1 . 
           [0024]      FIG. 12  is a schematic diagram of another exemplary gear train according to the present invention. 
           [0025]      FIG. 13  is a schematic diagram of another exemplary gear train according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0027]    As shown in  FIG. 1 , an exemplary gear train of an automatic transmission according to the present invention includes an input shaft  10 , an output shaft  20 , a transmission case  30  and a first, second, and third planetary gear set PG 1 , PG 2 , and PG 3 . 
         [0028]    The input shaft  10  receives power generated by an engine (not shown) through a torque converter (not shown). 
         [0029]    The output shaft  20  outputs power from the gear train. 
         [0030]    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. A first pinion gear P 1  is connected to the first planet carrier PC 1  and engaged with the first sun gear S 1  and the first ring gear R 1 . 
         [0031]    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. A second pinion gear P 2  is connected to the second planet carrier PC 2  and engaged with the second sun gear S 2  and the second ring gear R 2 . 
         [0032]    The third planetary gear set PG 3  is a single pinion planetary gear set and includes a third sun gear S 3 , a third planet carrier PC 3  and a third ring gear R 3  as operating members. A third pinion gear P 3  is connected to the third planet carrier PC 3  and engaged with the third sun gear S 3  and the third ring gear R 3 . 
         [0033]    The first sun gear S 1  is selectively connected to the input shaft  10 , selectively connected with the first planet carrier PC 1  and selectively connected to the transmission case  30 . 
         [0034]    The first planet carrier PC 1  is selectively connected to the transmission case  30  and is fixedly connected with the second ring gear R 2 . 
         [0035]    The first ring gear R 1  is fixedly connected to the output shaft  20 . 
         [0036]    The second sun gear S 2  is fixedly connected to the input shaft  10 . 
         [0037]    The second planet carrier PC 2  is fixedly connected with the third ring gear R 3 . 
         [0038]    The third sun gear S 3  is fixed to the transmission case  30 . 
         [0039]    The third planet carrier PC 3  is selectively connected to the input shaft  10  and selectively connected with the first ring gear R 1 . 
         [0040]    The gear train further includes a plurality of friction members (C 1 , C 2 , C 3 , C 4 , B 1 , B 2 ) that selectively connect the operating member of the planetary gear sets PG 1 , PG 2 , and PG 3  with the input shaft  10 , the output shaft  20 , the transmission case  30  and one of the other operating members. 
         [0041]    The first clutch C 1  selectively connects the third planet carrier PG 3  to the input shaft  10  and the second clutch C 2  selectively connects the first sun gear S 1  to the input shaft  10 . 
         [0042]    The third clutch C 3  selectively connects the first sun gear S 1  with the first planet carrier PC 1  and the fourth clutch C 4  selectively connects the third planet carrier PC 3  with the first ring gear R 1 . 
         [0043]    The first brake B 1  selectively connects the first planet carrier PC 1  to the transmission case  30 . 
         [0044]    The first brake B 2  selectively connects the first sun gear S 1  to the transmission case  30 . 
         [0045]    A one-way clutch OWC may be disposed in parallel with the first brake B 1  and the one-way clutch OWC selectively connects the first planet carrier PC 1  to the transmission case  30 . 
         [0046]    As shown in  FIG. 2 , the automatic transmission may realize eighth forward speeds and one reverse speed by operations of two friction members in each shift-speed. 
         [0047]    That is, in the first forward speed, the fourth clutch C 4  and the first brake B 1  are operated or the fourth clutch C 4  and the one-way clutch OWC are operated. 
         [0048]    The fourth clutch C 4  and the second brake B 2  are operated in the second forward speed. 
         [0049]    The third clutch C 3  and the fourth clutch C 4  are operated in the third forward speed and the second clutch C 2  and the fourth clutch C 4  are operated in the fourth forward speed. 
         [0050]    In the fifth forward speed, the second clutch C 2  and the third clutch C 3  are operated or the first clutch C 1  and the fourth clutch C 4  are operated. 
         [0051]    The first clutch C 1  and the third clutch C 3  are operated in the sixth forward speed and the first clutch C 1  and the second clutch C 2  are operated in the seventh forward speed. 
         [0052]    The first clutch C 1  and the second brake B 2  are operated in the eighth forward speed and the second clutch C 2  and the first brake B 1  are operated in one reverse speed. 
         [0053]    Hereinafter, referring to  FIG. 3  to  FIG. 11 , shifting processes in the gear train according to various embodiments of the present invention will be described. 
         [0054]    The first sun gear S 1  is a first operating member N 1 , the first planet carrier PC 1  is a second operating member N 2  and the first ring gear R 1  is a third operating member N 3 . The second sun gear S 2  is a fourth operating member N 4 , the second planet carrier PC 2  is a the fifth operating member N 5  and the second ring gear R 2  is a sixth operating member N 6 . And third sun gear S 3  is a seventh operating member N 7 , the third planet carrier PC 3  is a the eighth operating member N 8  and the third ring gear R 3  is a ninth operating member N 9 . 
         [0055]    First Forward Speed 
         [0056]    In the first forward speed, the fourth clutch C 4  and the first brake B 1  are operated or the fourth clutch C 4  and the one-way clutch OWC are operated. 
         [0057]    Rotation speed of the input shaft  10  is transmitted to the fourth operating member N 4  and the second operating member N 2  and the sixth operating member N 6  are stopped by an operation of the first brake B 1  or the one-way clutch OWC. 
         [0058]    The fifth operating member N 5  rotates with the same rotational speed as the ninth operating member N 9 , and the eighth operating member N 8  rotates with the same rotational speed as the third operating member N 3  by an operation of the fourth clutch C 4 . Thus, the third operating member N 3  outputs the first forward speed as shown in  FIG. 3  by combination of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 . 
         [0059]    Second Forward Speed 
         [0060]    The fourth clutch C 4  and the second brake B 2  are operated in the second forward speed. 
         [0061]    Rotation speed of the input shaft  10  is transmitted to the fourth operating member N 4 , the second operating member N 2  rotates with the same rotational speed as the sixth operating member N 6 , and the fifth operating member N 5  rotates with the same rotational speed as the ninth operating member N 9 . 
         [0062]    The eighth operating member N 8  rotates with the same rotational speed as the third operating member N 3  by an operation of the fourth clutch C 4 . 
         [0063]    Thus, the third operating member N 3  outputs the second forward speed as shown in  FIG. 4  by combination of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 . 
         [0064]    Third Forward Speed 
         [0065]    The third clutch C 3  and the fourth clutch C 4  are operated in the third forward speed. 
         [0066]    The fourth operating member N 4  rotates with the same rotational speed as the input shaft  10  and the fifth operating member N 5  rotates with the same rotational speed as the ninth operating member N 9 . 
         [0067]    The first planetary gear set PG 1  rotates as a whole by an operation of the third clutch C 3  and the eighth operating member N 8  rotates with the same rotational speed as the first planetary gear set PG 1  by an operation of the fourth clutch C 4 . 
         [0068]    Thus, the third operating member N 3  outputs the third forward speed as shown in  FIG. 5  by combination of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 . 
         [0069]    Fourth Forward Speed 
         [0070]    The second clutch C 2  and the fourth clutch C 4  are operated in the fourth forward speed. 
         [0071]    The rotational speed of the input shaft  10  is simultaneously transmitted to the first operating member N 1  and the fourth operating member N 4  by an operation of the second clutch C 2 . 
         [0072]    The second operating member N 2  rotates with the same rotational speed as the sixth operating member N 6  and the fifth operating member N 5  rotates with the same rotational speed as the ninth operating member N 9 . 
         [0073]    The third operating member N 3  rotates with the same rotational speed as the eighth operating member N 8  by an operation of the fourth clutch C 4 . 
         [0074]    Thus, the third operating member N 3  outputs the fourth forward as shown in  FIG. 6  speed by combination of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 . 
         [0075]    Fifth Forward Speed 
         [0076]    In the fifth forward speed, the second clutch C 2  and the third clutch C 3  are operated or the first clutch C 1  and the fourth clutch C 4  are operated. 
         [0077]    When the second clutch C 2  and the third clutch C 3  are operated, the rotational speed of the input shaft  10  is simultaneously transmitted to the first operating member N 1  and the fourth operating member N 4  and the first planetary gear set PG 1  and the second planetary gear set PG 2  integrally rotate as a whole. 
         [0078]    Thus, the third operating member N 3  outputs the fifth forward speed (the rotational speed of the input shaft  10 ) as shown in  FIG. 7  by combination of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 . 
         [0079]    When the first clutch C 1  and the fourth clutch C 4  are operated, the input shaft  10 , the eighth operating member N 8  and the output shaft  30  are directly connected. 
         [0080]    Thus, the third operating member N 3  outputs the fifth forward speed (the rotational speed of the input shaft  10 ). 
         [0081]    Sixth Forward Speed 
         [0082]    The first clutch C 1  and the third clutch C 3  are operated in the sixth forward speed. 
         [0083]    The first planetary gear set PG 1  integrally rotates as a whole by an operation of the third clutch C 3 , the rotational speed of the input shaft  10  is transmitted to the fourth operating member N 4  and the fifth operating member N 5  rotates with the same rotational speed as the ninth operating member N 9 . 
         [0084]    Thus, the third operating member N 3  outputs the sixth forward speed as shown in  FIG. 8  by combination of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 . 
         [0085]    Seventh Forward Speed 
         [0086]    The first clutch C 1  and the second clutch C 2  are operated in the seventh forward speed. 
         [0087]    The rotational speed of the input shaft  10  is simultaneously transmitted to the first operating member N 1 , the fourth operating member N 4  and the eighth operating member N 8 , the second operating member N 2  rotates with the same rotational speed as the sixth operating member N 6 , and the fifth operating member N 5  rotates with the same rotational speed as the ninth operating member N 9 . 
         [0088]    Thus, the third operating member N 3  outputs the seventh forward speed as shown in  FIG. 9  by combination of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 . 
         [0089]    Eighth Forward Speed 
         [0090]    The first clutch C 1  and the second brake B 2  are operated in the eighth forward speed. 
         [0091]    The rotational speed of the input shaft  10  is simultaneously transmitted to the fourth operating member N 4  and the eighth operating member N 8  and the first operating member N 1  is stopped by an operation of the second brake B 2 . 
         [0092]    The second operating member N 2  rotates with the same rotational speed as the sixth operating member N 6  and the fifth operating member N 5  rotates with the same rotational speed as the ninth operating member N 9 . 
         [0093]    Thus, the third operating member N 3  outputs the eighth forward speed as shown in  FIG. 10  by combination of the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 . 
         [0094]    One Reverse Speed 
         [0095]    The second clutch C 2  and the first brake B 1  are operated in one reverse speed. 
         [0096]    The rotational speed of the input shaft  10  is transmitted to the first operating member N 1  and the second operating member N 2  is stopped by an operation of the first brake B 1 . 
         [0097]    Thus, the third operating member N 3  outputs one reverse speed. 
         [0098]      FIG. 12  is a schematic diagram of another exemplary gear train according to the present invention. This gear train of the automatic transmission is similar to that described above and hereinafter, the different between them will be explained. 
         [0099]    An arrangement of the third clutch C 3  in various embodiments of the present invention is different from that described above and the third clutch C 3  selectively connects the third operating member N 3  with the second operating member N 2  and the sixth operating member N 6 . 
         [0100]      FIG. 13  is a schematic diagram of a gear train according to another exemplary embodiment of the present invention. 
         [0101]    This gear train of the automatic transmission of is similar to that described above and hereinafter, the differences will be explained. 
         [0102]    An arrangement of the third clutch C 3  in various embodiments of the present invention is different from that described above and the third clutch C 3  selectively connects the first operating member N 1  with the second operating member N 2 . In an above-described gear train of the automatic transmission, the third clutch C 3  selectively connects the first operating member N 1  with the second operating member N 2  and the sixth operating member N 6 . 
         [0103]    Operating elements and lever diagrams of the additional exemplary embodiments of the present invention are identical with that of the first exemplary embodiment of the present invention except for the third clutch C 3  so that detailed explanation will be omitted. 
         [0104]    The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.