Abstract:
The present invention provides a gear train of an automatic transmission to realize eight forward speed and two reverse speeds to improve power delivery performance and to reduce fuel consumption, by controlling two simple planetary gear sets and one compound planetary gear set through four clutches and two brakes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to Korean Patent Application No. 10-2009-0004186 filed on Jan. 19, 2009, 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 that realizes eight forward speeds. 
         [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]    In addition to various developments regarding four and five speed gear trains, a six speed automatic transmission has recently been developed. 
         [0010]    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 
       [0011]    Various aspects of the present invention are directed to provide a gear train of an automatic transmission for a vehicle having advantages of realizing eight forward speeds and two reverse speeds, improving power delivery performance, reducing fuel consumption, and improving reverse speed performance by controlling two simple planetary gear sets and one compound planetary gear set through four clutches and two brakes. 
         [0012]    In an aspect of the present invention, the gear train of an automatic transmission for vehicle may include, a first planetary gear set PG 1  that is a double pinion planetary gear set, and includes a first sun gear S 1  that is operated as a fixed element, a first ring gear R 1  that forms a first intermediate output path MOP 1  to output a reduced rotation speed, and a first planetary carrier PC 1  that forms an input path IP that is connected to an input shaft IS and forms a second intermediate output path MOP 2  to output the same speed, a second planetary gear set PG 2  that is a single pinion planetary gear set, and includes a second sun gear S 2  that is directly connected to the first intermediate output path MOP 1  to form a first intermediate input path MIP 1 , a second planetary carrier PC 2  that forms a third intermediate output path MOP 3 , and a second ring gear R 2  that is directly connected to the second intermediate input path MIP 2  to form a second intermediate input path MIP 2 , a third planetary gear set PG 3  that is a single pinion planetary gear set and a double pinion planetary gear set that are combined with each other to be a compound planetary gear set like a Ravingneaux type, and includes a third sun gear S 3  that is engaged with a long pinion P 1  to form first and second variable input paths VIP 1  and VIP 2  that are variably connected to the first intermediate output path MOP 1  and the third intermediate output path MOP 3 , and is simultaneously operated as an optional fixed element, a third planetary carrier PC 3  that is variably connected to the input shaft IS to form a fourth variable input path VIP 4 , and is simultaneously operated as a fixed element, a third ring gear R 3  that is connected to an output shaft OS to form a final output path OP, and a fourth sun gear S 4  that is engaged with a short pinion P 2  to be variably connected to the first intermediate output path MOP 1  and to form a third variable input path VIP 3 , and a plurality of friction members including a plurality of clutches that are disposed on the first, second, third, and fourth variable input paths (VIP 1 -VIP 4 ) and a plurality of brakes (B 1  and B 2 ) that are disposed between an operating member as a fixed element and a transmission housing (H). 
         [0013]    The plurality of friction members may include a first clutch C 1  that is disposed on the third variable input path VIP 3 , a second clutch C 2  that is disposed on the first variable input path. VIP 1 , a third clutch C 3  that is disposed on the second variable input path VIP 2 , a fourth clutch C 4  that is disposed on the fourth variable input path VIP 4 , a first brake B 1  that is disposed between the third planetary carrier PC 3  and the transmission housing (H), and a second brake  132  that is disposed between the third sun gear S 3  and the transmission housing (H). 
         [0014]    The second and third clutches C 2  and C 3  and the first and second brakes B 1  and B 2  may be disposed between the second planetary gear set PG 2  and the third planetary gear set PG 3 , and the first and fourth clutches C 1  and C 4  may be disposed in a rear side of the third planetary gear set PG 3 . 
         [0015]    As stated above, the first and second planetary gear sets PG 1  and PG 2  that are simple planetary gear sets and the third planetary gear set PG 3  that is a compound planetary gear set are controlled by the four friction elements of the clutches (C 1 , C 2 , C 3 , and C 4 ) and two brakes B 1  and B 2  to realize eight forward speeds and two reverse speeds, and to improve power delivery performance and reduce fuel consumption. 
         [0016]    Also, two friction elements are operated in the respective speeds, such that the capacity of the hydraulic pump is downsized and the control efficiency of the hydraulic pressure is improved. 
         [0017]    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 
         [0018]      FIG. 1  is a schematic diagram of a gear train according to an exemplary embodiment of the present invention. 
           [0019]      FIG. 2  is an operational chart of frictional members employed in a gear train according to the exemplary embodiment of the present invention. 
           [0020]      FIG. 3  is a lever diagram of a gear train according to an exemplary embodiment of the present invention. 
       
    
    
       [0021]    It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
         [0022]    In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0023]    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. 
         [0024]    Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
         [0025]      FIG. 1  is a schematic diagram of a gear train according to an exemplary embodiment of the present invention. A gear train of the present invention includes first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3  that are disposed on the same shaft axis, four clutches (C 1 , C 2 , C 3 , C 4 ) as clutch means, and two brakes B 1  and B 2  as brake means. 
         [0026]    Accordingly, rotational speed of an input shaft IS is changed via the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3  and output through an output shaft OS. The first planetary gear set PG 1  is disposed close to an engine and the second and third planetary gear sets PG 2  and PG 3  are sequentially disposed. 
         [0027]    The input shaft IS is an input member and indicates a turbine shaft in a torque converter (not shown). The input shaft IS receives a converted engine torque from the torque converter, and the output shaft OS, which is an output member, outputs a drive torque to vehicle wheels through an output gear and a differential. 
         [0028]    The first planetary gear set PG 1  is a double pinion planetary gear set and includes a sun gear S 1 , a planet carrier PC 1 , and a ring gear R 1  as three rotational elements according to a conventional art. 
         [0029]    The first sun gear S 1  is fixedly connected to a transmission housing H, and the first planetary gear PC 1  is directly connected to the input shaft IS. 
         [0030]    The first sun gear S 1  as a first rotational element N 1  is fixedly connected to the transmission housing H so that the first sun gear S 1  is operated as a fixed element, the first ring gear R 1  as a second rotational element N 2  forms a first intermediate output path MOP 1  to output a reduced rotation speed as an output element, and the first planetary carrier PC 1  as a third rotational element N 3  is directly connected to an input shaft IS to form an input path (IP) and simultaneously forms a second intermediate output path MOP 2  to output the same speed as the input speed. 
         [0031]    The second planetary gear set PG 2  is a single pinion planetary gear set and includes a second sun gear S 2 , a planet carrier PC 2 , and a second ring gear R 2 , as is already known to a person skilled in the art. 
         [0032]    In the second planetary gear set PG 2 , the second sun gear S 2  is directly connected to the first ring gear R 1  and the second ring gear R 2  is directly connected to the first planetary carrier PC 1 . 
         [0033]    As shown, a first intermediate input path MIP 1  is formed between the second sun gear S 2  of the second planetary gear set PG 2  as the fourth rotational element N 4  and the first intermediate output path MOP 1  that is directly connected to the second rotational element N 2 , the second planetary carrier PC 2  as the fifth rotational element N 5  is an optionally fixed element to simultaneously form a third intermediate output path MOP 3 , and the second ring gear R 2  as a sixth rotational element N 6  forms a second intermediate input path MIP 2  that is directly connected to the second intermediate output path MOP 2  of the third rotational element N 3 . 
         [0034]    According to such configurations, the different rotation speeds are transferred to the fourth rotational element N 4  of the second sun gear S 2  and the sixth rotational element N 6  of the second ring gear R 2 , and the second planetary carrier PC 2  outputs the single rotation speed. 
         [0035]    The third planetary gear set PG 3  includes a single pinion planetary gear set and a double pinion planetary gear set to have a Ravingneaux type of planetary gear set that shares the ring gear and the planetary carrier. 
         [0036]    The third planetary gear set PG 3  includes a third ring gear R 3 , a third planet carrier PC 3 , a third sun gear S 3  engaged with a long pinion P 1 , and a fourth sun gear S 4  engaged with a short pinion P 2 . 
         [0037]    The third sun gear S 3  as a seventh rotational element N 7  forms first and second variable input paths VIP 1  and VIP 2  that are optionally connected to the first intermediate output path MOP 1  of the first ring gear R 1  and the third intermediate output path MOP 3  of the second planetary carrier PC 2 , and simultaneously variably connected to the transmission housing (H). 
         [0038]    The fourth sun gear S 4  as a tenth rotational element N 10  forms the third variable input path VIP 3  that is variably connected to the first intermediate output path MOP 1 , the third planetary carrier PC 3  as a eight rotational element N 8  forms the fourth variable input path VIP 4  that is variably connected to the input shaft IS, simultaneously the third planetary carrier PC 3  is variably connected to a transmission housing (H) to operate as a fixed element, and the third ring gear R 3  as a ninth rotational element N 9  is directly connected to an output shaft OS to form a final output path (OP). 
         [0039]    Here, the second clutch C 2  is disposed on the first variable input path VIP 1 , the power of the first ring gear R 1  is selectively transmitted to the third sun gear S 3  according to the operation of the second clutch C 2 , the third clutch C 3  is disposed on the second variable input path VIP 2 , and the power of the second planetary carrier PC 2  is selectively transmitted to the third sun gear S 3  according to the operation of the third clutch C 3 . 
         [0040]    Also, the first clutch C 1  is disposed on the third variable input path VIP 3 , the rotation of the first ring gear R 1  is selectively transmitted to the fourth sun gear S 4  depending on the operation of the first clutch C 1 , the fourth clutch C 4  is disposed on the fourth variable input path VIP 4 , and the rotation of the input shaft IS is selectively transmitted to the third planetary carrier PC 3  depending on the operation of the fourth clutch C 4 . 
         [0041]    Also, the third planetary carrier PC 3  and the third sun gear S 3  are optionally fixed elements, and for this purpose the first brake B 1  is disposed in parallel with the one-way clutch (F) between the third planetary carrier PC 3  and the transmission housing (H) in the present invention, and the second brake B 2  is disposed between the third sun gear S 3  and the transmission housing (H). 
         [0042]    The sequential order (the first, the second, the third . . . ) is given to the clutch and the brake so as to discriminate them, and the sequential order is determined from the element that is first operated in the shift-up process from the first forward speed. 
         [0043]    With the scheme as described above, the rotational speed of the input shaft IS is transmitted to the first, second, and third planetary gear sets PG 1 , PG 2 , and PG 3 , and is changed into one of the eight forward speeds and two reverse speeds and output through the output path OP of the output shaft OS. 
         [0044]    The first, second, third, and fourth clutches C 1 , C 2 , C 3 , and C 4  and the first, second, and third brakes B 1 , B 2 , and B 3  can be enabled as multi-plate hydraulic pressure friction devices that are frictionally engaged by hydraulic pressure. 
         [0045]    Further, the second and third clutches C 2  and C 3  and the first and second brakes B 1  and B 2  are disposed between the second planetary gear set PG 2  and the third planetary gear set PG 3 , and the first and fourth clutches C 1  and C 4  are disposed in the rear side of the third planetary gear set PG 3 . 
         [0046]      FIG. 2  is an operational chart of frictional members employed in a gear train according to the exemplary embodiment of the present invention. As shown in  FIG. 2 , two friction elements are operated in each shift range. 
         [0047]    That is, the first clutch C 1  and the one-way clutch (F) are operated in the first forward speed. 
         [0048]    The first clutch C 1  and the second brake B 2  are operated in the second forward speed. 
         [0049]    The first and second clutches C 1  and C 2  are operated in the third forward speed. 
         [0050]    The first and third clutches C 1  and C 3  are operated in the fourth forward speed. 
         [0051]    The first and fourth clutches C 1  and C 4  are operated in the fifth forward speed. 
         [0052]    The third and fourth clutches C 3  and C 4  are operated in the sixth forward speed. 
         [0053]    The second and fourth clutch C 2  and C 4  are operated in the seventh forward speed. 
         [0054]    The fourth clutch C 4  and the second brake B 2  are operated in the eighth forward speed. 
         [0055]    The second clutch C 2  and the first brake B 1  are operated in the first reverse speed. 
         [0056]    The third clutch C 3  and the first brake B 1  arc operated for the speed to be changed in the second reverse speed. 
         [0057]    The “o” in  FIG. 2  means that the vehicle is in a coasting condition (i.e., a driver takes the foot from an accelerator pedal such that the vehicle may run by its momentum down a steep hill). 
         [0058]      FIG. 3  is a lever diagram of a gear train according to the first exemplary embodiment of the present invention. In  FIG. 3 , a lower horizontal line represents “0” rotational speed, and an upper horizontal line represents “1.0” rotational speed, which is the same as the rotational speed of the input shaft IS. 
         [0059]    Three vertical lines of the first planetary gear set PG 1  sequentially denote the first sun gear S 1  as the first rotational element N 1 , the first ring gear R 1  as the second rotational element N 2 , and the first planetary carrier PC 1  of the third rotational element N 3  from the left side, and distances between them are determined depending on a gear ratio (teeth number of sun gear/teeth number of ring gear) of the first planetary gear set PG 1 . 
         [0060]    Three vertical lines of the second planetary gear set PG 2  sequentially denote the second sun gear S 2  as the fourth rotational element N 4 , the second planetary carrier PC 2  as the fifth rotational element N 5 , and the second ring gear R 2  as the sixth rotational element N 6  from the left side, and distances between them are determined depending on a gear ratio (teeth number of sun gear/teeth number of ring gear) of the second planetary gear set PG 2 . 
         [0061]    Four vertical lines of the third planetary gear set PG 3  sequentially denote the third sun gear S 3  as the seventh rotational element N 7 , the third planetary carrier PC 3  as the eighth rotational element N 8 , the third ring gear R 3  as the ninth rotational element N 9 , and the fourth sun gear S 4  as the tenth rotational element N 10  from the left side, and distances between them are determined depending on a gear ratio (teeth number of sun gear/teeth number of ring gear) of the third planetary gear set PG 3 . 
         [0062]    Determining the positions of the rotational elements is obvious to a person skilled in the art, so a detailed explanation will be omitted. 
       First Forward Speed 
       [0063]    In the first forward speed, the first clutch C 1  and the one-way clutch (F) are operated as shown in  FIG. 2 . 
         [0064]    Accordingly, in the first planetary gear set PG 1 , the first rotational element N 1  is fixed and the rotation power is inputted to the third rotational element N 3  through the input path (IP), the reduced rotation speed is outputted through the first intermediate output path MOP 1 , and simultaneously the same rotation speed is outputted through the second intermediate output path MOP 2 . 
         [0065]    The rotation power of the first intermediate output path MOP 1  and the second intermediate output path MOP 2  are transmitted to the fourth rotational element N 4  and the sixth rotational element N 6  of the second planetary gear set PG 2  through the first intermediate input path MIP 1  and the second intermediate input path MIP 2 , and simultaneously the rotation power is transmitted to the tenth rotational element N 10 , that is, the fourth sun gear S 4  of the third planetary gear set PG 3 , through the third variable input path VIP 3  by the first clutch C 1 . 
         [0066]    While the rotation power is inputted to the tenth rotational element N 10  and the eighth operating element N 8  is fixed by the first brake B 1 , the first speed line SP 1  is formed in the third planetary gear set PG 3 , the speed with a length of D 1  between the crossing point of the first speed line SP 1  and the vertical line of the ninth rotational element N 9  and the zero line (horizontal line) is outputted to generate the maximum gear ratio of 4.562 in the first forward speed (rotation speed of the input shaft IS/rotation speed of the output shaft OS). 
         [0067]    At this time, the rotation is inputted to the second planetary gear set PG 2  through the fourth rotational element N 4  and the sixth rotational element N 6 , but this does not affect the gear shifting. 
       Second Forward Speed 
       [0068]    The second brake B 2  is operated to realize the second forward speed from the first forward speed. 
         [0069]    That is, while the rotation power is inputted to the tenth rotational element N 10  by the operation of the first clutch C 1  as the first forward speed, the seventh rotational element N 7  is a fixed element by the operation of the second brake B 2  to form a second speed line SP 2 , and the speed with the length of D 2  is outputted through the ninth rotational element N 9  as an output element, therein the gear ratio is about 2.782 that is less than that of the first forward speed. 
       Third Forward Speed 
       [0070]    As shown in  FIG. 2 , the second brake B 2  that is operated in the second forward speed is released, and the second clutch C 2  is operated in the third forward speed. 
         [0071]    Then, like the above second forward speed, while the rotation power is inputted to the tenth rotational element N 10  by the operation of the first clutch C 1 , the second clutch C 2  is operated, such that the rotation power of the first intermediate output path MOP 1  is simultaneously transferred to the seventh rotational element N 7  and the tenth rotational element N 10  and the third planetary gear set PG 3  output the same speed as that of the input to form the third speed line SP 3 . The speed with the length of D 3  is outputted through the N 9  as an output element, and therein the gear ratio is about 1.940 that is less than that of the second forward speed. 
       Fourth Forward Speed 
       [0072]    As shown in  FIG. 2 , the second clutch C 2  that was operated during the third forward speed is released, and the third clutch C 3  is operated in the fourth forward speed. 
         [0073]    Then, like the third forward speed, while the rotation power is inputted to the tenth rotational element N 10  by the operation of the first clutch C 1 , the third clutch C 3  is operated, such that the rotation power of the third intermediate output path MOP 3  is inputted to the seventh rotational element N 7  through the second variable input path VIP 2  to form the fourth speed line SP 4 . The speed with the length of D 4  is outputted through the N 9  as an output element, and therein the gear ratio is about 1.606 that is less than that of the third forward speed. 
       Fifth Forward Speed 
       [0074]    As shown in  FIG. 2 , the first clutch C 1  that was operated during the fourth forward speed is released, and the fourth clutch C 4  is operated in the fifth forward speed. 
         [0075]    Then, like the fourth forward speed, while the rotation power is inputted to the tenth rotational element N 10  by the operation of the first clutch C 1 , the fourth clutch C 4  is operated, such that the rotation power of the input shaft IS is inputted to the eighth rotational element N 8  through the fourth variable input path VIP 4  to form the fifth speed line SP 5 . The speed with the length of D 5  is outputted through the N 9  as an output element, and therein the gear ratio is about 1.260 that is less than that of the fourth forward speed. 
       Sixth Forward Speed 
       [0076]    As shown in  FIG. 2 , the first clutch C 1  that was operated during the fifth forward speed is released, and the third clutch C 3  is operated in the sixth forward speed. 
         [0077]    Then, like the fifth forward speed, while the rotation power is inputted to the eighth rotational element N 8  by the operation of the fourth clutch C 4  through the fourth variable input path VIP 4 , the third clutch C 3  is operated, such that the rotation power of the third intermediate output path MOP 3  is inputted to the seventh rotational element N 7  through the second variable input path VIP 2  to form a sixth speed line SP 6 . The speed with the length of D 6  is outputted through the N 9  as an output element, and therein the gear ratio is about 0.942 as an overdrive condition. 
       Seventh Forward Speed 
       [0078]    As shown in  FIG. 2 , the third clutch C 3  that was operated during the sixth forward speed is released, and the third clutch C 2  is operated in the seventh forward speed. 
         [0079]    Then, like the sixth forward speed, while the rotation power is inputted to the eighth rotational element N 8  by the operation of the fourth clutch C 4  through the fourth variable input path VIP 4 , the second clutch C 2  is operated such that the rotation power of the first intermediate output path MOP 1  is inputted to the seventh rotational element N 7  through the first variable input path VIP 1  to form the seventh speed line SP 7 . The speed with the length of D 7  is outputted through the N 9  as an output element, and therein the gear ratio is about 0.814 as an overdrive condition. 
       Eighth Forward Speed 
       [0080]    As shown in  FIG. 2 , the third clutch C 2  that was operated during the seventh forward speed is released, and the second brake B 2  is operated in the eighth forward speed. 
         [0081]    Then, like the fifth forward speed, while the rotation power is inputted to the eighth rotational element N 8  by the operation of the fourth clutch C 4  through the fourth variable input path VIP 4 , the second brake B 2  is operated such that the seventh rotational element N 7  is fixed to form the eighth speed line SP 8 . The speed with the length of D 8  is outputted through the N 9  as an output element, and therein the gear ratio is about 0.680 as an overdrive condition. 
       First Reverse Speed 
       [0082]    As shown in  FIG. 2 , the second clutch C 2  and the first brake B 1  are operated in the first reverse speed. 
         [0083]    Accordingly, while the rotation power is inputted to the third rotational element N 3  through the input path(IP) in the first planetary gear set PG 1 , the first rotational element N 1  is a fixed element, the reduced speed is outputted through the first intermediate output path MOP 1 , and the same speed is outputted through the second intermediate output path MOP 2 . 
         [0084]    The rotation power of the first intermediate output path MOP 1  and the second intermediate output path MOP 2  are respectively transferred to the fourth rotational element N 4  and the sixth rotational element N 6  of the second planetary gear set PG 2 , and simultaneously the rotation power of the first intermediate output path MOP 1  is transferred to the third sun gear S 3  as the seventh rotational element N 7  of the third planetary gear set PG 3  through the first variable input path VIP 1  by the second clutch C 2 . 
         [0085]    Then, the rotation power is inputted to the seventh rotational element N 7  of the third planetary gear set PG 3 , and the eighth operating element N 8  is fixed by the operation of the first brake B 1  to form a first reverse speed line SR 1 . The reverse speed is outputted with the length of REV 1  from zero to the first reverse speed line SR 1 , and therein the gear ratio is −4.117. 
         [0086]    At this time, the fourth rotational element N 4  and the sixth rotational element N 6  are rotated in the second planetary gear set PG 2 , but these rotations do not affect shifting. 
       Second Reverse Speed 
       [0087]    As shown in  FIG. 2 , the second clutch C 2  that was operated during the first reverse speed is released, and the third clutch C 3  is operated in the second reverse speed. 
         [0088]    Then, like the first reverse speed, while the eighth rotational element N 8  is fixed by the operation of the first brake B 1 , the third clutch C 3  is operated such that the rotation power of the third intermediate output path MOP 3  is transferred to the seventh rotational element N 7  through the second variable input path VIP 2  to form a second reverse speed line SR 2 . The reverse speed is outputted with the length of REV 2  from zero to the second reverse speed line SR 2 , and therein the gear ratio is −2.439. 
         [0089]    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. 
         [0090]    More specifically, omitting a one-way brake (F) that is disposed corresponding to the first brake B 1  and operating the first brake B 1  in the first forward speed are known to a person of ordinary skill in this art. 
         [0091]    For convenience in explanation and accurate definition in the appended claims, the term “rear” is used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
         [0092]    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.