Abstract:
A speed-reducing gear unit is provided for causing a reduced-speed rotation output member to have a reduced rotation that is slower than rotation of an input shaft. The reduced-speed rotation output member is switched between a reduced-speed rotation state and a free rotation state by rotation state switching means. The reduced-speed rotation of the reduced-speed rotation output member is selectively transferred to fourth and first elements of a speed-changing dual planetary gear unit via first and third control clutches. The rotation of the input shaft is transferred to a second element via a second control clutch. Rotations of the first and second elements are selectively restricted by first and second control brakes. A third element is connected to an output shaft. This makes it possible to provide a high-efficiency automatic transmission that achieves seven or more forward gear ratios so as to allow optimal extraction of engine performance in a high vehicle speed region and reduce the vehicle speed change at the time of a gear shift and therefore provide a good feeling, by adding gear speeds including a locked-up speed at a high gear speed side so that adjacent gear ratios are closer to each other.

Description:
INCORPORATION BY REFERENCE  
         [0001]    The disclosure of Japanese Patent Application No. 2001-001594 filed on Jan. 9, 2001 and No. 2001-021759 filed on Jan. 30, 2001, each including the specification, drawings and abstract, is incorporated herein by reference in its entirety.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of Invention  
           [0003]    The invention relates to an automatic transmission that shifts rotation of an input shaft at a selected one of a plurality of speed ratios and transfers the thus-shifted rotation to an output shaft by engaging and disengaging control clutches and control brakes connected to various elements of a speed-changing dual planetary gear unit connected to the input shaft.  
           [0004]    2. Description of Related Art  
           [0005]    U.S. Pat. No. 5,106,352 discloses an automatic transmission that includes: a speed-changing dual planetary gear unit having first and second sun gears, a long pinion that directly meshes with the first sun gear and that meshes with the second sun gear via an intermediate pinion, a carrier that supports the long pinion and the intermediate pinion, and a ring gear that meshes with the long pinion and that is connected to an output shaft; and a speed-reducing planetary gear having a ring gear connected to an input shaft, a sun gear fixed to a transmission case, and a carrier that supports a pinion meshed with the ring gear and the sun gear. This automatic transmission achieves six forward gear ratios and one reverse gear ratio by selectively transferring the rotation of the carrier of the speed-reducing planetary gear unit that has been reduced in speed so that the rotation speed of the carrier is less than the rotation speed of the input shaft to the second and first sun gears through the use of first and third control clutches, and by selectively transferring the rotation of the input shaft to the carrier of the speed-changing dual planetary gear unit through the use of a second control clutch, and by selectively restricting the rotations of the first sun gear and the carrier of the speed-changing dual planetary gear unit through the use of first and second control brakes.  
           [0006]    This conventional automatic transmission has a small entire length, and is therefore suitable for a front-wheel drive vehicle with a transversely mounted engine. In recent years, however, there is a demand for an automatic transmission capable of achieving seven or more forward gear ratios that are appropriately spaced, in order to improve fuel economy and power transfer performance or to provide gear ratios that match a driver&#39;s taste.  
         SUMMARY OF THE INVENTION  
         [0007]    Accordingly, it is an object of the invention to provide a high-efficiency automatic transmission that achieves seven or more forward gear ratios so as to allow optimal extraction of engine performance in a high vehicle speed region and reduces changes in output torque during gear shifting by adding a gear speed including a locked-up speed at a high gear speed side so that adjacent gear ratios are closer to each other. This results in smooth gear to gear transitions and, thus, a smoother, more pleasurable ride. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:  
         [0009]    [0009]FIG. 1 is a skeleton diagram illustrating a first embodiment of the automatic transmission of the invention;  
         [0010]    [0010]FIG. 2 is a table showing the states of operation of control brakes and control clutches for various gear speeds in the first embodiment;  
         [0011]    [0011]FIG. 3 is a speed diagram indicating the rotation ratios of various elements of a planetary gear unit at the gear speeds in the first embodiment;  
         [0012]    [0012]FIG. 4 is a skeleton diagram illustrating a second embodiment;  
         [0013]    [0013]FIG. 5 is a table showing the states of operation of control brakes and control clutches for various gear speeds in the second embodiment;  
         [0014]    [0014]FIG. 6 is a speed diagram indicating the rotation ratios of various elements of a planetary gear unit at the gear speeds in the second embodiment;  
         [0015]    [0015]FIG. 7 is a skeleton diagram illustrating a third embodiment;  
         [0016]    [0016]FIG. 8 is a table showing the states of operation of control brakes and control clutches for various gear speeds in the third embodiment;  
         [0017]    [0017]FIG. 9 is a speed diagram indicating the rotation ratios of various elements of a planetary gear unit at the gear speeds in the third embodiment;  
         [0018]    [0018]FIG. 10 is a diagram illustrating that a first rotation control clutch is connected between a sun gear and a carrier of a speed-reducing planetary gear unit;  
         [0019]    [0019]FIG. 11 is another diagram illustrating that a first rotation control clutch is connected between a sun gear and a carrier of a speed-reducing planetary gear unit;  
         [0020]    [0020]FIG. 12 is a skeleton diagram illustrating a fourth embodiment;  
         [0021]    [0021]FIG. 13 is a skeleton diagram illustrating a fifth embodiment;  
         [0022]    [0022]FIG. 14 is a skeleton diagram illustrating a sixth embodiment;  
         [0023]    [0023]FIG. 15 is a table showing the states of operation of control brakes and control clutches for various gear speeds in the sixth embodiment;  
         [0024]    [0024]FIG. 16 is a speed diagram indicating the rotation ratios of various elements of a planetary gear unit at the gear speeds in the sixth embodiment;  
         [0025]    [0025]FIG. 17 is a skeleton diagram illustrating a seventh embodiment;  
         [0026]    [0026]FIG. 18 is a skeleton diagram illustrating an eighth embodiment;  
         [0027]    [0027]FIG. 19 is a skeleton diagram illustrating a ninth embodiment;  
         [0028]    [0028]FIG. 20 is a skeleton diagram illustrating a tenth embodiment;  
         [0029]    [0029]FIG. 21 is a skeleton diagram illustrating an eleventh embodiment;  
         [0030]    [0030]FIG. 22 is a speed diagram indicating the rotation ratios of various elements of a planetary gear unit at the gear speeds in the eleventh embodiment;  
         [0031]    [0031]FIG. 23 is a skeleton diagram illustrating a twelfth embodiment;  
         [0032]    [0032]FIG. 24 is a speed diagram indicating the rotation ratios of various elements of a planetary gear unit at the gear speeds in the twelfth embodiment;  
         [0033]    [0033]FIG. 25 is a skeleton diagram illustrating a thirteenth embodiment; and  
         [0034]    [0034]FIG. 26 is a speed diagram indicating the rotation ratios of various elements of a planetary gear unit at the gear speeds in the thirteenth embodiment. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0035]    A first preferred embodiment of the automatic transmission of the invention will be first described below with reference to the accompanying drawings. Referring to FIG. 1, an automatic transmission  10  in accordance with the invention is used to change the speed of the output rotation of a fluid torque converter  11  that is driven by, for example, a motor vehicle engine, and to transfer the speed-changed rotation to driving wheels. The automatic transmission  10  includes an input shaft  15 , a speed-reducing dual planetary gear unit  16 , a speed-changing dual planetary gear unit  17 , and an output shaft  18  that are sequentially supported on a common axis  13  within a transmission case  12  mounted on a vehicle body. The speed-reducing dual planetary gear unit  16  is formed by coupling and integrating the carrier C 1 , C 2  and ring gear R 1 , R 2  of two single-pinion type planetary gear mechanisms  51 ,  52 . Specifically, the speed-reducing dual planetary gear unit  16  includes a large-diameter sun gear S 1  and a small-diameter sun gear S 2  that are rotatably supported on the common axis  13 , stepped pinions  25  each formed by a small-diameter pinion  23  and a large-diameter pinion  24  that mesh with the large-diameter sun gear S 1  and the small-diameter sun gear S 2 , respectively, a common carrier C 1 , C 2  that rotatably supports the stepped pinions  25  and is rotatably supported on the common axis  13 , and a common ring gear R 1 , R 2  that meshes with the large-diameter pinions  24  and that is rotatably supported on the common axis  13 . The input shaft  15  is connected to the ring gear R 1 , R 2   
         [0036]    Second and first rotation control brakes B- 2 , B- 1  for selectively restricting rotations by connecting the large-diameter and small-diameter sun gears S 1 , S 2  to the transmission case  12  are connected to the large-diameter and small-diameter sun gears S 1 , S 2 , respectively. Therefore, the carrier C 1 , C 2 , as a reduced-speed rotation output member  55 , can be switched among a first reduced-speed rotation state in which the rotation of the small-diameter sun gear S 2  is restricted by the first rotation control brake B- 1  so that the carrier C 1 , C 2  has a first reduced-speed rotation that is slower than the rotation of the input shaft  15 , a second reduced-speed rotation state in which the rotation of the large-diameter sun gear S 1  is restricted by the second rotation control brake B- 2  so that the carrier C 1 , C 2  has a second reduced-speed rotation speed that is slower than the first reduced-speed rotation, and a free rotation state in which the first and second rotation control brakes B- 1 , B- 2  are in a disengaged state so that rotation is not restricted.  
         [0037]    The speed-reducing dual planetary gear unit  16  forms a speed-reducing gear unit  49  that is connected to the input shaft  15  and that generates the first and second reduced-speed rotations that are slower than the rotation of the input shaft  15 . The first and second rotation control brakes B- 1 , B- 2  form a rotation state switching means  50  for switching the carrier C 1 , C 2 , as the reduced-speed rotation output member  55 , between the reduced-speed rotation states and the free rotation state.  
         [0038]    The speed-changing dual planetary gear unit  17  is formed by connecting and integrating the carrier C 3 , C 4  and ring gear R 3 , R 4  of a single-pinion type planetary gear mechanism  53  and a double-pinion type planetary gear mechanism  54 . Specifically, the speed-changing dual planetary gear unit  17  includes first and second sun gears S 3 , S 4  rotatably supported on the common axis  13 , long pinions  34  that directly mesh with the first sun gear S 3  and that mesh with the second sun gear S 4  via intermediate pinions  33 , a common carrier C 3 , C 4  that rotatably supports the long pinions  34  and the intermediate pinions  33  and that is rotatably supported on the common axis  13 , and a common ring gear R 3 , R 4  that meshes with the long pinions  34  and that is rotatably supported on the common axis  13 . The ring gear R 3 , R 4  is connected to the output shaft  18 .  
         [0039]    Third and first control clutches C- 3 , C- 1  are provided for selectively connecting the carrier C 1 , C 2  of the speed-reducing dual planetary gear unit  16  to the first and second sun gears S 3 , S 4  of the speed-changing dual planetary gear unit  17 , respectively. A second control clutch C- 2  is provided for selectively connecting the input shaft  15  to the common carrier C 3 , C 4  of the speed-changing dual planetary gear unit  17 . The first sun gear S 3  and the carrier C 3 , C 4  are connected with first and second control brakes B- 3 , B- 4 , respectively, which selectively connect the first sun gear S 3  and the carrier C 3 , C 4  to the transmission case  12  so as to restrict rotation thereof. A one-way clutch F- 1  is provided for restricting reverse rotation of the carrier C 3 , C 4 .  
         [0040]    A pump impeller  45  of the fluid torque converter  11  is turned by the engine (not shown) so as to deliver oil. With a stator  46  receiving reaction force from oil, torque is generated on a turbine  47 . The input shaft  15  is connected to the turbine  47 . A lockup clutch  48  is provided for directly connecting the pump impeller  45  and the turbine  47 .  
         [0041]    The automatic transmission  10  constructed as described above is able to achieve gear ratios of 12 forward speeds and 2 reverse speeds by selectively engaging and disengaging the first to third control clutches C- 1  to C- 3 , and by restricting rotations of elements of the planetary gear units through selective actuation of the first and second control brakes B- 3 , B- 4  and the first and second rotation control brakes B- 1 , B- 2 . In the table of FIG. 2, solid circles in boxes of the control clutches and the control brakes corresponding to the gear speeds indicate a connected state for the control clutches, and a rotation restricting state for the control brakes. The column of gear ratios shows gear ratios (rotation speed of the input shaft  15 /rotation speed of the output shaft  18 ) of the gear speeds achieved in a case where a speed-reducing first planetary gear mechanism  51  formed by the large-diameter sun gear S 1 , the stepped pinions  25 , the carrier C 1  and the ring gear R 1  has a gear ratio λ1 of 0.778, and a speed-reducing second planetary gear mechanism  52  formed by the small-diameter sun gear S 2 , the large-diameter pinions  24 , the carrier C 2  and the ring gear R 2  has a gear ratio λ2 of 0.361, and a speed-changing first planetary gear mechanism  53  formed by the first sun gear S 3 , the long pinions  34 , the carrier C 3  and the ring gear R 3  of the speed-changing dual planetary gear unit  17  has a gear ratio λ3 of 0.458, and a speed-changing second planetary gear mechanism  54  formed by the second sun gear S 4 , the intermediate pinions  33 , the long pinions  34 , the carrier C 4  and the ring gear R 4  has a gear ratio λ4 of 0.375.  
         [0042]    In the speed-reducing first and second planetary gear mechanisms  51 ,  52  and the speed-changing first planetary gear mechanism  53  that are of the single-pinion type, a relationship among a sun gear rotation speed Ns, a carrier rotation speed Nc, a ring gear rotation speed Nr, and the gear ratio λ of the planetary gear mechanism is expressed by equation (1). In the double-pinion type speed-changing second planetary gear mechanism  54 , a relationship among the sun gear rotation speed Ns, the carrier rotation speed Nc, the ring gear rotation speed Nr, and the gear ratio λ of the planetary gear mechanism is expressed by equation (2). The gear ratio of each gear speed is calculated based on equations (1) and (2). Where the numbers of teeth of the large-diameter, small-diameter, first and second sun gears S 1 , S 2 , S 3 , S 4  are expressed as Zs 1 , Zs 2 , Zs 3 , Zs 4 , and the numbers of teeth of the ring gears R 1 , R 2 , R 3 , R 4  are expressed as Zr 1 , Zr 2 , Zr 3 , Zr 4 , the gear ratios of the speed-reducing first and second planetary gear mechanisms  51 ,  52  and the speed-changing first and second planetary gear mechanisms  53 ,  54  can be written as λ1=Zs 1 /Zr 1 , λ2=Zs 2 /Zr 2 , λ3=Zs 3 /Zr 3 , λ4=Zs 4 /Zr 4 , respectively.  
         Nr=(1+λ)Nc−λNs  (1)  
         Nr=(1−λ)Nc+λNs  (2)  
         [0043]    If the first and second rotation control brakes B- 1 , B- 2  are selectively actuated and the first to third control clutches C- 1  to C- 3  are selectively connected and the first and second control brakes B- 3 , B- 4  are selectively actuated, the speed ratios of the various elements of the speed-reducing dual planetary gear unit  16  and the speed-changing dual planetary gear unit  17  become as indicated by a speed diagram shown in FIG. 3. In the speed diagram, the elements of the planetary gear mechanisms, that is, the sun gears, the carriers and the ring gears, are arranged in the direction of a horizontal axis at intervals corresponding to the gear ratios, and the speed ratios are indicated corresponding to the various elements in the direction of a vertical axis. In FIG. 3, the speed diagram of the speed-reducing dual planetary gear unit  16  and the speed diagram of the speed-changing dual planetary gear unit  17  are shown side by side. As for the speed-reducing first and second planetary gear mechanisms  51 ,  52  of the speed-reducing dual planetary gear unit  16 , the carriers C 1 , C 2  and the ring gears R 1 , R 2  are respectively integrated. Therefore, the speed ratio of the common carrier C 1 , C 2  and the speed ratio of the common ring gear R 1 , R 2  are indicated by a vertical line denoted by C 1 , C 2  and a vertical line denoted by R 1 , R 2 , respectively. The speed ratio of the first sun gear S 1  and the speed ratio of the second sun gear S 2  are indicated by a vertical line denoted by S 1  and a vertical line denoted by S 2 , respectively. As for the single-pinion type first planetary gear mechanism  51 , an interval between the vertical line of the carrier C 1  and the vertical line of the ring gear R 1  is regarded as the gear ratio λ1 of the first planetary gear mechanism  51 , and the vertical line of the sun gear S 1  is disposed at a side of the vertical line of the carrier C 1  opposite from the vertical line of the ring gear R 1 , with an interval a/λ1 being left between the vertical line of the first sun gear S 1  and the vertical line of the carrier C 1 . Likewise, as for the single-pinion type second planetary gear mechanism  52 , an interval a between the vertical line of the carrier C 2  and the vertical line of the ring gear R 2  is regarded as the gear ratio λ2 of the second planetary gear mechanism  52 , and the vertical line of the second sun gear S 2  is disposed at a side of the vertical line of the carrier C 2  opposite from the vertical line of the ring gear R 2 , with an interval a/λ2 being left between the vertical line of the second sun gear S 2  and the vertical line of the carrier C 2 .  
         [0044]    As for the speed-changing first and second planetary gear mechanisms  53 ,  54  of the speed-changing dual planetary gear unit  17 , the carriers C 3 , C 4  and the ring gears R 3 , R 4  are respectively integrated. Therefore, the speed ratio of the common carrier C 3 , C 4  and the speed ratio of the common ring gear R 3 , R 4  are indicated on a vertical line denoted by C 3 , C 4  and a vertical line denoted by R 3 , R 4 , respectively. The speed ratio of the first sun gear S 3  and the speed ratio of the second sun gear S 4  are indicated by a vertical line denoted by S 3  and a vertical line denoted by S 4 , respectively. As for the single-pinion type speed-changing first planetary gear mechanism  53 , an interval b between the vertical line of the carrier C 3  and the vertical line of the ring gear R 3  is regarded as the gear ratio λ3 of the speed-changing first planetary gear mechanism  53 , and the vertical line of the first sun gear S 3  is disposed at a side of the vertical line of the carrier C 3  opposite from the vertical line of the ring gear R 3 , with an interval b/λ3 being left between the vertical line of the first sun gear S 3  and the vertical line of the carrier C 3 . As for the double-pinion type speed-changing second planetary gear mechanism  54 , an interval b between the vertical line of the carrier C 4  and the vertical line of the ring gear R 4  is regarded as the gear ratio λ4 of the speed-changing second planetary gear mechanism  54 , and the vertical line of the second sun gear S 4  is disposed at a side of the vertical line of the carrier C 4  where the vertical line of the ring gear R 4  is also disposed, with an interval b/λ4 being left between the vertical line of the second sun gear S 4  and the vertical line of the carrier C 4 . In the speed diagrams, B- 1  to B- 4  and C- 1  to C- 3  are indicated at points where the first and second rotation control brakes B- 1 , B- 2 , the first to third control clutches C- 1  to C- 3 , and the first and second control brakes B- 3 , B- 4  are selectively actuated.  
         [0045]    In the speed diagram of the speed-changing dual planetary gear unit  17  prepared as described above, the elements corresponding to the four vertical lines will be termed first element, second element, third element and fourth element, in the order of arrangement of the four vertical lines. Namely, the speed-changing dual planetary gear unit  17  has the first element, the second element, the third element and the fourth element corresponding to the order of four elements arranged at intervals corresponding to each gear ratio in the speed diagram. Furthermore, as shown in FIG. 3, the speed diagram indicates the gear ratios of each element with vertical lines, i.e., the first element, the second element, the third element and the fourth element are arranged in order of rotational speed excepting the fifth forward speed and the sixth forward speed in which each element is rotated integrally. Namely, the speed-changing dual planetary gear unit  17  has the first element, the second element, the third element and the fourth element arranged in order of rotational speed. In the first embodiment, the first sun gear S 3 , as the first element, is connected to the third control clutch C- 3  and the first control brake B- 3 ; the carrier C 3 , as the second element, is connected to the second control clutch C- 2  and the second control brake B- 4 ; the ring gear R 3 , R 4 , as the third element, is connected to the output shaft  18 ; and the second sun gear S 4 , as the fourth element, is connected to the first control clutch C- 1 .  
         [0046]    The operation for each gear speed will be described below. In the case of the first forward gear speed, the second rotation control brake B- 2 , forming the rotation state switching means  50 , is actuated to stop the rotation of the large-diameter sun gear S 1 , so that the carrier C 1 , C 2  as the reduced-speed rotation output member  55  is switched to the second reduced-speed rotation state. Furthermore, the first control clutch C- 1  is actuated to connect the carrier C 1 , C 2  and the second sun gear S 4 , and the one-way clutch F- 1  is actuated to restrict reverse rotation of the carrier C 3 , C 4 . Therefore, rotation of the input shaft  15  is reduced in speed to a second reduced-speed rotation that is slower than the rotation of the input shaft  15 , by the ring gear R 1 , R 2 , the large-diameter first sun gear S 1 , restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the ring gear R 3 , R 4  via the first control clutch C- 1 , the second sun gear S 4 , and the carrier C 3 , C 4  whose reverse rotation is restricted by the one-way clutch F- 1  so as to bear reaction force, thereby forwardly driving the output shaft  18  at a gear ratio of 4.741 of the first gear speed. It is also possible to restrict rotation of the carrier C 3 , C 4  by actuating the second control brake B- 4 .  
         [0047]    In the case of the second forward gear speed, the small-diameter second sun gear S 2  is restricted in rotation by the first rotation control brake B- 1 , which forms the rotation state switching means  50 , so that the carrier C 1 , C 2  is switched to the first reduced-speed rotation state. Furthermore, the control clutch C- 1  is actuated to connect the carrier C 1 , C 2  and the second sun gear S 4 , and the one-way clutch F- 1  is actuated to restrict reverse rotation of the carrier C 3 , C 4 . Therefore, rotation inputted to the input shaft  15  is reduced in speed to a first reduced-speed rotation that is slower than the rotation of the input shaft  15  and is faster than the second reduced-speed rotation, by the ring gear R 1 , R 2 , the small-diameter second sun gear S 2 , restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the ring gear R 3 , R 4  via the first control clutch C 1 , the second sun gear S 4 , and the carrier C 3 , C 4  whose reverse rotation is restricted by the one-way clutch F- 1  so as to bear reaction force, thereby forwardly driving the output shaft  18  at a gear ratio of 3.630 of the second gear speed.  
         [0048]    In the case of the third forward gear speed, the second rotation control brake B- 2  is actuated to restrict rotation of the large-diameter first sun gear S 1 , so that the carrier C 1 , C 2  is switched to the second reduced-speed rotation state. Furthermore, the first control clutch C- 1  is actuated to connect the carrier C 1 , C 2  and the second sun gear S 4 , and the first control brake B- 3  is actuated to restrict rotation of the first sun gear S 3 . Therefore, rotation inputted to the input shaft  15  is reduced in speed to the second reduced-speed rotation, by the ring gear R 1 , R 2 , the large-diameter first sun gear S 1 , restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the ring gear R 3 , R 4  via the first control clutch C- 1 , the second sun gear S 4 , the first sun gear S 3  restricted in rotation so as to bear reaction force, and the carrier C 3 , C 4 , thereby forwardly driving the output shaft  18  at a gear ratio of 2.709 of the third gear speed.  
         [0049]    In the case of the fourth forward gear speed, the first rotation control brake B- 1  is actuated to restrict rotation of the small-diameter second sun gear S 2 , so that the carrier C 1 , C 2  is switched to the first reduced-speed rotation state. Furthermore, the first control clutch C- 1  is actuated to connect the carrier C 1 , C 2  and the second sun gear S 4 , and the first control brake B- 3  is actuated to restrict rotation of the first sun gear S 3 . Therefore, rotation inputted to the input shaft  15  is reduced in speed to the first reduced-speed rotation, by the ring gear R 1 , R 2 , the small-diameter second sun gear S 2 , restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the ring gear R 3 , R 4  via the first control clutch C- 1 , the second sun gear S 4 , the first sun gear S 3 , restricted in rotation so as to bear reaction force, and the carrier C 3 , C 4 , thereby forwardly driving the output shaft  18  at a gear ratio of 2.074 of the fourth gear speed.  
         [0050]    In the case of the fifth forward gear speed, the second rotation control brake B- 2  is actuated to restrict rotation of the large-diameter first sun gear S 1 , so that the carrier C 1 , C 2  is switched to the second reduced-speed rotation state. Furthermore, the first control clutch C- 1  and the third control clutch C- 3  are actuated to connect the carrier C 1 , C 2  to the second sun gear S 4  and the first sun gear S 3 , respectively. Therefore, rotation of the input shaft  15  is reduced in speed to the second reduced-speed rotation, by the ring gear R 1 , R 2 , the large-diameter first sun gear S 1 , restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the second and first sun gears S 4 , S 3  via the first and third control clutches C- 1 , C- 3  so that the ring gear R 3 , R 4  is rotated via the carrier C 3 , C 4  in accordance with the rotation of the first and second sun gears S 3 , S 4 . As a result, the output shaft  18  is forwardly driven at a gear ratio of 1.778 of the fifth gear speed.  
         [0051]    In the case of the sixth forward gear speed, the first rotation control brake B 1  is actuated to restrict rotation of the small-diameter sun gear S 2 , so that the carrier C 1 , C 2  is switched to the first reduced-speed rotation state. Furthermore, the first control clutch C- 1  and the third control clutch C- 3  are actuated to connect the carrier C 1 , C 2  to the second sun gear S 4  and the first sun gear S 3 . Therefore, rotation of the input shaft  15  is reduced in speed to the first reduced-speed rotation, by the ring gear R 1 , R 2 , the small-diameter second sun gear S 2 , restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the second and first sun gears S 4 , S 3  via the first and third control clutches C- 1 , C- 3  so that the ring gear R 3 , R 4  is rotated via the carrier C 3 , C 4  in accordance with the rotation of the first and second sun gears S 3 , S 4 . As a result, the output shaft  18  is forwardly driven at a gear ratio of 1.361 of the sixth gear speed.  
         [0052]    In the case of the seventh forward gear speed, the second rotation control brake B- 2  is actuated to restrict rotation of the large-diameter sun gear S 1 , so that the carrier C 1 , C 2  is switched to the second reduced-speed rotation state. Furthermore, the first control clutch C- 1  and the second control clutch C- 2  are actuated to connect the carrier C 1 , C 2  to the second sun gear S 4  and connect the input shaft  15  to the carrier C 3 , C 4 . Therefore, rotation of the input shaft  15  is reduced in speed to the second reduced-speed rotation, by the ring gear R 1 , R 2 , the large-diameter first sun gear S 1 , restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the second sun gear S 4  via the first control clutch C- 1 . Simultaneously, the rotation of the input shaft  15  is directly transferred to the carrier C 3 , C 4  via the second control clutch C- 2 . As a result, the ring gear R 3 , R 4  is rotated in accordance with the difference between the rotation of the second sun gear S 4  and the rotation of the carrier C 3 , C 4 , thereby forwardly driving the output shaft  18  at a gear ratio of 1.196 of the seventh gear speed.  
         [0053]    In the case of the eighth forward gear speed, the first rotation control brake B- 1  is actuated to restrict rotation of the small-diameter sun gear S 2 , so that the carrier C 1 , C 2  is switched to the first reduced-speed rotation state. Furthermore, the first control clutch C- 1  and the second control clutch C- 2  are actuated to connect the carrier C 1 , C 2  to the second sun gear S 4  and connect the input shaft  15  to the carrier C 3 , C 4 . Therefore, rotation of the input shaft  15  is reduced in speed to the first reduced-speed rotation, by the ring gear R 1 , R 2 , the small-diameter second sun gear S 2 , restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the second sun gear S 4  via the first control clutch C- 1 . Simultaneously, the rotation inputted to the input shaft  15  is directly transferred to the carrier C 3 , C 4  via the second control clutch C- 2 . As a result, the ring gear R 3 , R 4  is rotated in accordance with the difference between the rotation of the second sun gear S 4  and the rotation of the carrier C 3 , C 4 , thereby forwardly driving the output shaft  18  at a gear ratio of 1.100 of the eighth gear speed.  
         [0054]    In the case of the ninth forward gear speed, the first, second and third control clutches C- 1 , C- 2 , C- 3  are connected to connect the first and second sun gears S 3 , S 4  via the carrier C 1 , C 2  as the reduced-speed rotation output member  55 . Furthermore, the first and second rotation control brakes B- 1 , B- 2 , as the rotation state switching means  50 , remain un-actuated so that the carrier C 1 , C 2  is in a freely rotatable state. Therefore, rotation of the input shaft  15  is directly transferred to the carrier C 3 , C 4  of the speed-changing dual planetary gear unit  17  via the second control clutch C- 2 , so that the ring gear R 3 , R 4  is rotated via the interlocked first and second sun gears S 3 , S 4 . As a result, the ring gear R 3 , R 4  is forwardly driven at a gear ratio of 1.000 of the ninth gear speed.  
         [0055]    In the case of the tenth forward gear speed, the first rotation control brake B 1  is actuated to restrict rotation of the small-diameter second sun gear S 2  so that the first carrier C 1 , C 2  is switched to the first reduced-speed rotation state. Furthermore, the third control clutch C- 3  and the second control clutch C- 2  are actuated to connect the carrier C 1 , C 2  to the first sun gear S 3  and connect the input shaft  15  to the carrier C 3 , C 4 . Therefore, rotation of the input shaft  15  is reduced in speed to the first reduced-speed rotation, by the ring gear R 1 , R 2 , the small-diameter second sun gear S 2 , restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the first sun gear S 3  via the third control clutch C- 3 . Simultaneously, the rotation of the input shaft  15  is directly transferred to the carrier C 3 , C 4  via the second control clutch C- 2 . As a result, the ring gear R 3 , R 4  is rotated in accordance with the difference between the rotation of the first sun gear S 3  and the rotation of the carrier C 3 , C 4 , thereby forwardly driving the output shaft  18  at a gear ratio of 0.892 of the tenth gear speed.  
         [0056]    In the case of the eleventh forward gear speed, the second rotation control brake B- 2  is actuated to restrict rotation of the large-diameter sun gear S 1 , so that the carrier C 1 , C 2  is switched to the second reduced-speed rotation state. Furthermore, the third control clutch C- 3  and the second control clutch C- 2  are actuated to connect the carrier C 1 , C 2  to the first sun gear S 3  and connect the input shaft  15  to the carrier C 3 , C 4 . Therefore, rotation of the input shaft  15  is reduced in speed to the second reduced-speed rotation, by the ring gear R 1 , R 2 , the large-diameter sun gear S 1  restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the first sun gear S 3  via the third control clutch C- 3 . Simultaneously, the rotation of the input shaft  15  is directly transferred to the carrier C 3 , C 4  via the second control clutch C- 2 . As a result, the ring gear R 3 , R 4  is rotated in accordance with the difference between the rotation of the first sun gear S 3  and the rotation of the carrier C 3 , C 4 , thereby forwardly driving the output shaft  18  at a gear ratio of 0.833 of the eleventh gear speed.  
         [0057]    In the case of the twelfth forward gear speed, the second control clutch C- 2  is actuated to connect the input shaft  15  to the carrier C 3 , C 4 , and the first control brake B- 3  is actuated to restrict rotation of the first sun gear S 3 . Therefore, rotation of the input shaft  15  is transferred to the carrier C 3 , C 4  via the second control clutch C- 2  to rotate the ring gear R 3 , R 4  with the rotation-restricted first sun gear S 3  bearing reaction force. As a result, the output shaft  18  is forwardly driven at a gear ratio of 0.686 of the twelfth gear speed.  
         [0058]    In the case of the first reverse gear speed, the second rotation control brake B- 2  is actuated to restrict rotation of the large-diameter sun gear S 1 , so that the carrier C 1 , C 2  is switched to the first reduced-speed rotation state. Furthermore, the third control clutch C- 3  is actuated to connect the carrier C 1 , C 2  to the first sun gear S 3 , and the second control brake B- 4  is actuated to restrict rotation of the carrier C 1 , C 2 . Therefore, rotation of the input shaft  15  is reduced in speed to the second reduced-speed rotation via the ring gear R 1 , R 2 , the large-diameter first sun gear S 1 , restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the first sun gear S 3  via the third control clutch C- 3  so as to reversely rotate the ring gear R 3 , R 4  with the rotation-restricted carrier C 3 , C 4  bearing reaction force. As a result, the output shaft  18  is reversely driven at a gear ratio of 3.879 of the first reverse gear speed.  
         [0059]    In the case of the second reverse gear speed, the first rotation control brake B- 1  is actuated to restrict rotation of the small-diameter sun gear S 2 , so that the carrier C 1 , C 2  is switched to the first reduced-speed rotation state. Furthermore, the third control clutch C- 3  is actuated to connect the carrier C 1 , C 2  to the first sun gear S 3 , and the second control brake B- 4  is actuated to restrict rotation of the carrier C 1 , C 2 . Therefore, rotation of the input shaft  15  is reduced in speed to the first reduced-speed rotation via the ring gear R 1 , R 2 , the small-diameter sun gear S 2  restricted in rotation and bearing reaction force, and the carrier C 1 , C 2 . The rotation is then transferred to the first sun gear S 3  via the third control clutch C 3  so as to reversely rotate the ring gear R 3 , R 4  with the rotation-restricted carrier C 3 , C 4  bearing reaction force. As a result, the output shaft  18  is reversely driven at a gear ratio of 2.970 of the second reverse gear speed.  
         [0060]    As is apparent from the speed diagram of FIG. 3 indicating the rotation ratios of the large-diameter, small-diameter, first and second sun gears S 1  to S 4 , the carrier C 1 , C 2 , the carrier C 3 , C 4 , the ring gear R 1 , R 2  and the ring gear R 3 , R 4  in the various gear speeds where the rotation speed of the ring gear R 1 , R 2  of the speed-reducing dual planetary gear unit  16  connected to the input shaft  15  is defined as 1, the rotation ratios, that is, the gear ratios, of the common ring gear R 3 , R 4  of the gear speeds are arranged at suitable intervals. According to the automatic transmission in accordance with the invention, it is possible to achieve twelve forward speeds and two reverse speeds that are suitably spaced. Furthermore, none of the sun gears, carriers or ring gears rotate at very high speeds in any of the forward or reverse speeds.  
         [0061]    A second embodiment will next be described with reference to FIG. 4. The second embodiment is the same as the first embodiment in the speed-changing dual planetary gear unit  17 , the first to third clutches C- 1  to C- 3 , the first and second control brakes B- 3 , B 4 , the one-way clutch F- 1 , etc., which are represented by like reference characters in the drawings, and will not be described again. A speed-reducing dual planetary gear unit  60  that distinguishes the second embodiment from the first embodiment will only be described.  
         [0062]    In the speed-reducing dual planetary gear unit  60 , a sun gear S 1  and a carrier C 1  of a double-pinion type planetary gear mechanism  65  and a sun gear S 2  and a carrier C 2  of a single-pinion type planetary gear mechanism  66  are connected and integrated. Specifically, the speed-reducing dual planetary gear unit  60  includes a common sun gear S 1 , S 2  rotatably supported on a common axis  13 , long pinions  62  meshed with the sun gear S 1 , S 2 , a common carrier C 1 , C 2  that rotatably supports the long pinions  62  and intermediate pinions  63  meshed with the long pinions  62  and that is rotatably supported on the common axis  13 , and ring gears R 2 , R 1  that mesh with the long pinions  62  and the intermediate pinions  63 , respectively, and that are rotatably supported on the common axis  13 . An input shaft  15  is connected to the ring gear R 2 , which precedes the ring gear R 1  in the transfer path.  
         [0063]    First and second rotation control brakes B- 1 , B- 2  for connecting the common sun gear S 1 , S 2  and the later-stage ring gear R 1 , respectively, to a transmission case  12  are connected to the sun gear S 1 , S 2  and the ring gear R 1 , respectively. Therefore, the carrier C 1 , C 2 , as a reduced-speed rotation output member  55 , is switched among a first reduced-speed rotation state in which the rotation of the sun gear S 1 , S 2  is restricted by the first rotation control brake B- 1  so that the carrier C 1 , C 2  has a first reduced-speed rotation that is slower than the rotation of the input shaft  15 , a second reduced-speed rotation state in which the rotation of the ring gear R 1  is restricted by the second rotation control brake B- 2  so that the carrier C 1 , C 2  has a second reduced-speed rotation speed that is slower than the first reduced-speed rotation, and a free rotation state in which the first and second rotation control brakes B- 1 , B- 2  are in a disengaged state so that rotation is not restricted.  
         [0064]    The speed-reducing dual planetary gear unit  60  forms a speed-reducing gear unit  49  that is connected to the input shaft  15  and that generates the first and second reduced-speed rotations that are slower than the rotation of the input shaft  15 . The first and second rotation control brakes B- 1 , B- 2  form rotation state switching means  50  for switching the carrier C 1 , C 2 , as the reduced-speed rotation output member  55 , among the reduced-speed rotation states and the free rotation state.  
         [0065]    The second embodiment is substantially the same as the first embodiment, in that the rotation of the input shaft  15  and the first or second reduced-speed rotations generated on the carrier C 1 , C 2  of the speed-reducing planetary gear unit  60  are transferred to the second and first sun gears S 4 , S 3  and the common carrier C 3 , C 4  of the speed-changing dual planetary gear unit  17  via the first to third control clutches C- 1  to C- 3 , and that the first sun gear S 3  and the carrier C 3 , C 4  are selectively restricted in rotation by the first and second control brakes B- 3 , B- 4  so as to shift the rotation of the input shaft  15  to twelve forward speeds and two reverse speeds. This feature will not be described in detail again. The states of operation of the control clutches and the control brakes for the gear speeds are shown in FIG. 5. In the second embodiment, the states of operation of the control brakes and the control clutches are interchanged between the second gear speed and the third gear speed and between the fourth gear speed and the fifth gear speed, in comparison with the first embodiment.  
         [0066]    [0066]FIG. 5 shows, in the column of gear ratio, the gear ratios (rotation speed of the input shaft  15 /rotation speed of the output shaft  18 ) of the gear speeds achieved in a case where a speed-reducing planetary gear mechanism  65  formed by the sun gear S 1 , the long pinions  62 , the intermediate pinions  63 , the carrier CI and the ring gear R 1  of the speed-reducing dual planetary gear unit  60  has a gear ratio λ1 of 0.273, and a speed-reducing second planetary gear mechanism  66  formed by the sun gear S 2 , the long pinions  62 , the carrier C 2  and the ring gear R 2  has a gear ratio λ2 of 0.391, and a speed-changing first planetary gear mechanism  53  formed by a first sun gear S 3 , long pinions  34 , a carrier C 3  and a ring gear R 3  of the speed-changing dual planetary gear unit  17  has a gear ratio λ3 of 0.556, and a speed-changing second planetary gear mechanism  54  formed by a second sun gear S 4 , intermediate pinions  33 , the long pinions  34 , a carrier C 4  and a ring gear R 4  has a gear ratio λ4 of 0.417.  
         [0067]    The speed diagram of the second embodiment is shown in FIG. 6. In the second embodiment as well, the first sun gear S 3  as the first element is connected to the third control clutch C- 3  and the first control brake B- 3 , and the carrier C 3 , C 4  as the second element is connected to the second control clutch C- 2  and the second control brake B- 4 , and the ring gear R 3 , R 4  as the third element is connected to the output shaft  18 , and the second sun gear S 4  as the fourth element is connected to the first control clutch C- 1 .  
         [0068]    An embodiment in which a single-type planetary gear unit is employed for a speed-reducing gear unit will next be described. A third embodiment is the same as the first embodiment in the speed-changing dual planetary gear unit  17 , the first to third clutches C- 1  to C- 3 , the first and second control brakes B- 3 , B- 4 , the one-way clutch F- 1 , etc., which are represented in FIG. 7 by comparable reference characters and will not be described again. A speed-reducing planetary gear unit  70  and a connection relationship between the speed-reducing planetary gear unit  70  and the speed-changing dual planetary gear unit  17  will only be described below.  
         [0069]    The speed-reducing planetary gear unit  70  includes a sun gear S 2  rotatably supported on a common axis  13 , pinions  71  meshed with the sun gear S 2 , a carrier C 2  that rotatably supports the pinions  71  and that is rotatably supported on the common axis  13 , and a ring gear R 2  that meshes with the pinions  71  and that is rotatably supported on the common axis  13 . An input shaft  15  is connected to the ring gear R 2 . A rotation control clutch C- 4  is designed to selectively connect the carrier C 2  to the ring gear R 2 . A rotation control brake B 2  is designed to selectively restrict rotation of the sun gear S 2 . Therefore, the carrier C 2  as a reduced-speed rotation output member  55  is switched among an input rotation state in which the carrier C 2  is connected to the ring gear R 2  by the rotation control clutch C- 4  so as to be rotated at the same rotation speed as the input rotation speed of the input shaft  15 , a reduced-speed rotation state in which rotation of the sun gear S 2  is restricted by the rotation control brake B- 2  so as to have a reduced-speed rotation that is slower than the rotation of the input shaft  15 , and a free rotation state in which the rotation control clutch C- 4  and the rotation control brake B- 2  remain un-actuated so that rotation is not restricted.  
         [0070]    The speed-reducing planetary gear unit  70  forms a speed-reducing gear unit  49  that is connected to the input shaft  15  and that generates the input rotation that is equal in speed to the rotation of the input shaft  15  and the reduced-speed rotation that is slower than the rotation of the input shaft  15 . The rotation control clutch C- 4  and the rotation control brake B- 2  form rotation state switching means  50  for switching the carrier C 2 , as the reduced-speed rotation output member  55 , between the reduced-speed rotation state and the free rotation state.  
         [0071]    The third embodiment, constructed as described above, is able to achieve gear ratios of nine forward speeds and two reverse speeds by selectively engaging and disengaging the first to third control clutches C- 1  to C- 3  and the rotation control clutch C- 4  and selectively actuating the first and second control brakes B- 3 , B- 4  and the rotation control brake B- 2  so as to restrict rotations of element members of the planetary gear unit.  
         [0072]    The states of operation of the control clutches and the control brakes for the gear speeds are shown in FIG. 8. FIG. 8 shows, in the column of gear ratio, the gear ratios (rotation speed of the input shaft  15 /rotation speed of the output shaft  18 ) of the gear speeds achieved in a case where the speed-reducing planetary gear unit  70  has a gear ratio λ2 of 0.417, and a speed-changing first planetary gear mechanism  53  formed by the first sun gear S 3 , the long pinions  34 , the carrier C 3  and the ring gear R 3  of the speed-changing dual planetary gear unit  17  has a gear ratio λ4 of 0.458, and a speed-changing second planetary gear mechanism  54  formed by the second sun gear S 4 , the intermediate pinions  33 , the long pinions  34 , the carrier C 4  and the ring gear R 4  has a gear ratio λ4 of 0.375.  
         [0073]    The speed diagram of the third embodiment is shown in FIG. 9. In the third embodiment as well, the first sun gear S 3  as the first element is connected to the third control clutch C- 3  and the first control brake B- 3 , the carrier C 3 , C 4 , as the second element, is connected to the second control clutch C- 2  and the second control brake B- 4 , the ring gear R 3 , R 4 , as the third element, is connected to the output shaft  18 , and the second sun gear S 4 , as the fourth element, is connected to the first control clutch C- 1 .  
         [0074]    Operations at the gear speeds will be described. In the case of the first forward gear speed, the rotation control brake B- 2 , forming the rotation state switching means  50 , is actuated to restrict rotation of the sun gear S 2 , so that the carrier C 2  as the reduced-speed rotation output member  55  is switched to the reduced-speed rotation state. Furthermore, the first control clutch C- 1  is actuated to connect the carrier C 2  to the second sun gear S 4 , and the one-way clutch F- 1  is actuated to restrict reverse rotation of the carrier C 3 , C 4 . Therefore, rotation of the input shaft  15  is reduced in speed to the reduced-speed rotation via the ring gear R 2 , the sun gear S 2 , restricted in rotation so as to bear reaction force, and the carrier C 2 . The rotation is then transferred to the ring gear R 3 , R 4  via the first control clutch C- 1 , the second sun gear S 4 , and the carrier C 3 , C 4  whose reverse rotation is restricted by the one-way clutch F-I so as to bear reaction force, thereby forwardly driving the output shaft  18  at a gear ratio of 3.778 of the first gear speed. It is also possible to restrict rotation of the carrier C 3 , C 4  by actuating the second control brake B- 4 .  
         [0075]    In the case of the second forward gear speed, the rotation control clutch C- 4 , forming the rotation state switching means  50 , is actuated to connect the carrier C 2  to the ring gear R 2 , so that the carrier C 2  is switched to the input rotation state in which the carrier C 2  rotates together with the input shaft  15 . Furthermore, the first control clutch C- 1  is actuated to connect the carrier C 2  to the second sun gear S 4 , and the one-way clutch F- 1  is actuated to restrict reverse rotation of the carrier C 3 , C 4 . Therefore, rotation inputted to the input shaft  15  is directly transferred as the input rotation to the carrier C 2  via the rotation control clutch C- 4 . The rotation is then transferred to the ring gear R 3 , R 4  via the first control clutch C- 1 , the second sun gear S 4 , and the carrier C 3 , C 4  whose reverse rotation is restricted by the one-way clutch F- 1  so as to bear reaction force, thereby forwardly driving the output shaft  18  at a gear ratio of 2.667 of the second gear speed.  
         [0076]    In the case of the third forward gear speed, the rotation control brake B- 2  is actuated to restrict rotation of the sun gear S 2 , so that the carrier C 2  is switched to the reduced-speed rotation state. Furthermore, the first control clutch C- 1  is actuated to connect the carrier C 2  to the second sun gear S 4 , and the first control brake B- 3  is actuated to restrict rotation of the first sun gear S 3 . Therefore, rotation of the input shaft  15  is reduced in speed to the reduced-speed rotation via the ring gear R 2 , the sun gear S 2  restricted in rotation so as to bear reaction force, and the carrier C 2 . The rotation is then transferred to the ring gear R 3 , R 4  via the first control clutch C- 1 , the second sun gear S 4 , the first sun gear S 3  whose rotation is restricted so as to bear reaction force, and the carrier C 3 , C 4 , thereby forwardly driving the output shaft  18  at a gear ratio of 2.159 of the third gear speed.  
         [0077]    In the case of the fourth forward gear speed, the rotation control clutch C- 4  is actuated to connect the carrier C 2  to the ring gear R 2 , so that the carrier C 2  is switched to the input rotation state in which the carrier C 2  rotates together with the input shaft  15 . Furthermore, the first control clutch C- 1  is actuated to connect the carrier C 2  to the second sun gear S 4 , and the first control brake B- 3  is actuated to restrict rotation of the first sun gear S 3 . Therefore, rotation of the input shaft  15  is directly transferred as the input rotation to the carrier C 2 . The rotation is then transferred to the ring gear R 3 , R 4  via the first control clutch C- 1 , the second sun gear S 4 , the first sun gear S 3  whose rotation is restricted so as to bear reaction force, and the carrier C 3 , C 4 , thereby forwardly driving the output shaft  18  at a gear ratio of 1.524 of the fourth gear speed.  
         [0078]    In the case of the fifth forward gear speed, the rotation control brake B- 2  is actuated to restrict rotation of the sun gear S 2 , so that the carrier C 2  is switched to the reduced-speed rotation state. Furthermore, the first and third control clutches C- 1 , C- 3  are actuated to connect the carrier C 2  to the second sun gear S 4  and to the first sun gear S 3 , respectively. Therefore, rotation of the input shaft  15  is reduced in speed to the reduced-speed rotation via the ring gear R 2 , the sun gear S 2 , restricted in rotation so as to bear reaction force, and the carrier C 2 . The rotation is then transferred to the second and first sun gears S 4 , S 3  via the first and third control clutches C- 1 , C- 3 , so that the ring gear R 3 , R 4  is rotated via the carrier C 3 , C 4  in accordance with the rotation of the first and second sun gears S 3 , S 4 . As a result, the output shaft  18  is forwardly rotated at a gear ratio of 1.417 of the fifth gear speed.  
         [0079]    In the case of the sixth forward gear speed, the rotation control brake B- 2  is actuated to restrict rotation of the sun gear S 2 , so that the carrier C 2  is switched to the reduced-speed rotation state. Furthermore, the first and second control clutches C- 1 , C- 2  are actuated to connect the carrier C 2  to the second sun gear S 4  and connect the input shaft  15  to the carrier C 3 , C 4 . Therefore, rotation of the input shaft  15  is reduced in speed to the reduced-speed rotation via the ring gear R 2 , the sun gear S 2 , restricted in rotation so as to bear reaction force, and the carrier C 2 . The rotation is then transferred to the second sun gear S 4  via the first control clutch C- 1 . Simultaneously, the rotation of the input shaft  15  is directly transferred to the carrier C 3 , C 4  via the second control clutch C- 2 . Hence, the ring gear R 3 , R 4  is rotated in accordance with the difference between the rotation of the second sun gear S 4  and the rotation of the carrier C 3 , C 4 . As a result, the output shaft  18  is forwardly rotated at a gear ratio of 1.124 of the sixth gear speed.  
         [0080]    In the case of the seventh forward gear speed, the first, second and third control clutches C- 1 , C- 2 , C- 3  are connected so that the first and second sun gears S 3 , S 4  are connected via the carrier C 2  as the reduced-speed rotation output member  55 . Furthermore, the rotation control clutch C- 4  and the rotation control brake B- 4 , which are the rotation state switching means  50 , are left un-actuated state, so that the carrier C 2  is in the free rotation state. Therefore, rotation inputted to the input shaft  15  is directly transferred to the carrier C 3 , C 4  of the speed-changing dual planetary gear unit  17  via the control clutch C- 2 , so as to rotate the ring gear R 3 , R 4  via the interlocked first and second sun gears S 3 , S 4 . As a result, the output shaft  18  is forwardly driven at a gear ratio of 1.000 of the seventh gear speed.  
         [0081]    In the case of the eighth forward gear speed, the rotation control brake B- 2  is actuated to restrict rotation of the sun gear S 2 , so that the carrier C 2  is switched to the reduced-speed rotation state. Furthermore, the third control clutch C- 3  and the second control clutch C- 2  are actuated to connect the carrier C 2  to the first sun gear S 3  and connect the input shaft  15  to the carrier C 3 , C 4 , respectively. Therefore, rotation of the input shaft  15  is reduced in speed via the ring gear R 2 , the sun gear S 2 , restricted in rotation so as to bear reaction force, and the carrier C 2 . The rotation is then transferred to the first sun gear S 3  via the third control clutch C- 3 . Simultaneously, the rotation of the input shaft  15  is directly transferred to the carrier C 3 , C 4  via the second control clutch C- 2 . Hence, the ring gear R 3 , R 4  is rotated in accordance with the difference between the rotation of the first sun gear S 3  and the rotation of the carrier C 3 , C 4 . As a result, the output shaft  18  is forwardly driven at a gear ratio of 0.881 of the eighth gear speed.  
         [0082]    In the case of the ninth forward gear speed, the second control clutch C- 2  is actuated to connect the input shaft  15  to the carrier C 3 , C 4 , and the first control brake B- 3  is actuated to restrict rotation of the first sun gear S 3 . Therefore, rotation of the input shaft  15  is transferred to the carrier C 3 , C 4  via the second control clutch C- 2 , so as to rotate the ring gear R 3 , R 4  with the first sun gear S 3  bearing reaction force. As a result, the output shaft  18  is forwardly driven at a gear ratio of 0.686 of the ninth gear speed.  
         [0083]    In the case of the first reverse gear speed, the rotation control brake B- 2  is actuated to restrict rotation of the second sun gear S 2 , so that the carrier C 2  is switched to the reduced-speed rotation state. Furthermore, the third control clutch C- 3  is actuated to connect the carrier C 2  to the first sun gear S 3 , and the second control brake B- 4  is actuated to restrict rotation of the carrier C 3 , C 4 . Therefore, rotation of the input shaft  15  is reduced in speed to the reduced-speed rotation via the ring gear R 2 , the second sun gear S 2 , restricted in rotation so as to bear reaction force, and the carrier C 2 . The rotation is transferred to the first sun gear S 3  via the third control clutch C- 3 . The ring gear R 3 , R 4  is reversely rotated with the rotation-restricted carrier C 3 , C 4  bearing reaction force. As a result, the output shaft  18  is reversely driven at a gear ratio of 3.091 of the first reverse gear speed.  
         [0084]    In the case of the second reverse gear speed, the rotation control clutch C- 4  is actuated to connect the carrier C 2  to the ring gear R 2 , so that the carrier C 2  is switched to the input rotation state in which the carrier C 2  rotates together with the input shaft  15 . Furthermore, the third control clutch C- 3  is actuated to connect the carrier C 2  to the first sun gear S 3 , and the second control brake B- 4  is actuated to restrict rotation of the carrier C 3 , C 4 . Therefore, rotation of the input shaft  15  is directly transferred to the carrier C 2 , and is then transferred to the first sun gear S 3  via the third control clutch C- 3 . The ring gear R 3 , R 4  is reversely rotated with the rotation-restricted carrier C 3 , C 4  bearing reaction force. As a result, the output shaft  18  is reversely driven at a gear ratio of 2.182 of the second reverse gear speed.  
         [0085]    In the third embodiment, the carrier C 2  of the speed-reducing planetary gear unit  70  is caused to have the reduced-speed rotation that is slower than the rotation of the input shaft  15  by restricting rotation of the second sun gear S 2  through the use of the rotation control brake B- 2 . Furthermore, the carrier C 2  is caused to have the input rotation equal in speed to the rotation of the input shaft  15  by connecting the carrier C 2  to the ring gear R 2  via the rotation control clutch C- 4 . However, it is also possible to cause the reduced-speed rotation of the carrier C 2  by restricting rotation of the sun gear S 2  in the same manner and to cause the input rotation of the carrier C 2  by selectively connecting the carrier C 2  and the sun gear S 2  or connecting the ring gear R 2  and the sun gear S 2  through the use of the rotation control clutch C- 4  as indicated in FIGS. 10 and 11. In this case, the speed diagram of the speed-changing dual planetary gear unit  17  and the states of operation of the control brakes and the control clutches for the gear speeds are the same as in the third embodiment.  
         [0086]    Fourth and fifth embodiments employing a single-type planetary gear unit in which rotation of a sun gear is restricted as a speed-reducing planetary gear unit will be described with reference to FIGS. 12 and 13. In FIG. 12, a speed-reducing planetary gear unit  72  includes a sun gear S 2  restricted in rotation, a carrier C 2  supporting pinions  73  meshed with the sun gear S 2 , and a ring gear R 2  meshed with the pinions  73 . An input shaft  15  is connected to the ring gear R 2 . Therefore, the carrier C 2  is caused to have a second rotation that is slower than the rotation of the input shaft  15 , and the ring gear R 2  is caused to have a first rotation that is equal in speed to the rotation of the input shaft  15 .  
         [0087]    A connecting member  74  is disposed rotatably on a common axis  13 . The connecting member  74  is detachably connected to second and first sun gears S 4 , S 3  by first and third control clutches C- 1 , C- 3 , and is detachably connected to the ring gear R 2  and the carrier C 2  by first and second rotation control clutches C- 4 , C- 5 . Therefore, the connecting member  74 , as a reduced-speed rotation output member  55 , is switched among an input rotation state in which the connecting member  74  is connected to the ring gear R 2  via the first rotation control clutch C- 4  so that the connecting member  74  is rotated at an input rotation equal in speed to the rotation of the input shaft  15 , a reduced-speed rotation state in which the connecting member  74  is connected to the carrier C 2  via the second rotation control clutch C 5  so that the connecting member  74  is rotated at a reduced-speed rotation that is slower than the rotation of the input shaft  15 , and a free rotation state in which the first and second rotation control clutches C- 4 , C- 5  remain disengaged so that the connecting member  74  is not restricted in rotation.  
         [0088]    The speed-reducing planetary gear unit  72  and the connecting member  74  form a speed-reducing gear unit  49  that is connected to the input shaft  15  and that generates the input rotation equal in speed to the rotation of the input shaft  15  and that generates the reduced-speed rotation that is slower than the rotation of the input shaft  15 . The first and second rotation control clutches C- 4 , C- 5  form rotation state switching means  50  for switching the connecting member  74  as the reduced-speed rotation output member  55  between the reduced-speed rotation state and the free rotation state.  
         [0089]    The states of operation of the control brakes and the control clutches for the gear speeds are substantially the same as in the third embodiment if the second rotation control clutch C- 5  replaces the second rotation control brake B- 2 . The speed diagram of the speed-changing dual planetary gear unit  17  is the same as in the third embodiment.  
         [0090]    In FIG. 13, a speed-reducing planetary gear unit  72  includes a sun gear S 2  restricted in rotation, a carrier C 2  supporting pinions  73  meshed with the sun gear S 2 , and a ring gear R 2  meshed with the pinions  73 . A first control clutch C- 1  is provided between the carrier C 2  and a second sun gear S 4 . A second control clutch C- 3  is provided between the carrier C 2  and a first sun gear S 3 . A first rotation control clutch C- 4  is provided between an input shaft  15  and the carrier C 2 . A second rotation control clutch C- 5  is provided between the input shaft  15  and the ring gear R 2 . Therefore, the carrier C 2 , as a reduced-speed rotation output member  55 , is switched among an input rotation state in which the carrier C 2  is connected to the input shaft  15  via the first rotation control clutch C- 4  so that the carrier C 2  rotates at an input rotation equal in speed to the rotation of the input shaft  15 , a reduced-speed rotation state in which the input shaft  15  is connected to the ring gear R 2  via the second rotation control clutch C- 5  so that the carrier C 2  rotates slower than the input shaft  15 , and a free rotation state in which the first and second rotation control clutches C- 4 , C- 5  remain disengaged so that rotation of the carrier C 2  is not restricted.  
         [0091]    The speed-reducing planetary gear unit  72  forms a speed-reducing gear unit  49  that is connected to the input shaft  15  and that generates a first rotation equal in speed to the rotation of the input shaft  15  and that generates a reduced-speed rotation that is slower than the rotation of the input shaft  15 . The first and second rotation control clutches C- 4 , C- 5  form rotation state switching means  50  for switching the carrier C 2  as the reduced-speed rotation output member  55  between the reduced-speed rotation state and the free rotation state. In this case, the states of operation of the control brakes and the control clutches for the gear speeds are substantially the same as in the third embodiment if the second rotation control clutch C- 5  replaces the second rotation control brake B- 2 . The speed diagram of the speed-changing dual planetary gear unit  17  is the same as in the third embodiment.  
         [0092]    Next described will be other embodiments that employ a single-type planetary gear unit as a speed-reducing gear unit. A sixth embodiment has a construction that can be obtained by removing the rotation control clutch C- 4  from the construction of the third embodiment. Components corresponding to those of the third embodiment are represented by comparable reference characters in FIG. 14, and will not be described in detail again. In this case, a carrier C 2  as a reduced-speed rotation output member  55  is switched between a reduced-speed rotation state in which a sun gear S 2  is restricted in rotation by a rotation control brake B- 2  so that the carrier C 2  rotates at a reduced-speed rotation that is slower than the rotation of an input shaft  15 , and a free rotation state in which the rotation control brake B- 2  remains disengaged so that the carrier C 2  is not restricted in rotation.  
         [0093]    The speed-reducing planetary gear unit  70  forms a speed-reducing gear unit  49  that is connected to the input shaft  15  and that generates a first rotation equal in speed to the rotation of the input shaft  15  and that generates a reduced-speed rotation that is slower than the rotation of the input shaft  15 . The first and second rotation control clutches C- 4 , C- 5  form rotation state switching means  50  for switching the carrier C 2  as the reduced-speed rotation output member  55  between the reduced-speed rotation state and the free rotation state.  
         [0094]    The states of operation of the control clutches and the control brakes for the gear speeds shown in FIG. 15 are equivalent to states thereof shown by a table obtained by eliminating from the table of FIG. 8 the rows of the gear speeds of 2nd, 4th and Rev2 in which the rotation control clutch C- 4  is actuated and by renumbering the remaining rows of gear speeds sequentially from the top. The operations of the speed-reducing planetary gear unit  70  and the speed-changing dual planetary gear unit  17  for the gear speeds are substantially the same as those for the corresponding gear speeds in the third embodiment, except for the gear ratios of the gear speeds. With regard to these points, description will be omitted. The column of gear ratios in FIG. 15 shows gear ratios of the gear speeds achieved in a case where the speed-reducing planetary gear unit  70  has a gear ratio λ2 of 0.556; a speed-changing first planetary gear mechanism  53  formed by a first sun gear S 3 , long pinions  34 , a carrier C 3  and a ring gear R 3  of the speed-changing dual planetary gear unit  17  has a gear ratio λ3 of 0.458; and a speed-changing second planetary gear mechanism  54  formed by a second sun gear S 4 , intermediate pinions  33 , the long pinions  34 , a carrier C 4  and a ring gear R 4  of the speed-changing dual planetary gear unit  17  has a gear ratio λ4 of 0.375.  
         [0095]    A speed diagram of the sixth embodiment is shown in FIG. 16. In the sixth embodiment as well, the first sun gear S 3  as the first element is connected to the third control clutch C- 3  and the first control brake B- 3 , and the carrier C 3 , C 4  as the second element is connected to the second control clutch C- 2  and the second control brake B- 4 , and the ring gear R 3 , R 4  as the third element is connected to the output shaft  18 , and the second sun gear S 4  as the fourth element is connected to the first control clutch C- 1 .  
         [0096]    Seventh and eighth embodiments employing a single-type planetary gear unit in which rotation of a sun gear is restricted as a speed-reducing planetary gear unit will next be described with reference to FIGS. 17 and 18. The seventh embodiment has a construction equivalent to a construction obtained by removing the first rotation control clutch C- 4  from the construction of the fourth embodiment. Components of the seventh embodiment corresponding to those of the fourth embodiment are represented by comparable reference characters in FIG. 17, and will not be described in detail again. In this case, a connecting member  74 , as a reduced-speed rotation output member  55 , is switched between a reduced-speed rotation state in which the connecting member  74  is connected to a carrier C 2  via a rotation control clutch C- 5  so that the connecting member  74  is rotated at a reduced-speed rotation that is slower than the rotation of an input shaft  15 , and a free rotation state in which the rotation control clutch C- 5  remains disengaged so that the connecting member  74  is not restricted in rotation.  
         [0097]    The speed-reducing planetary gear unit  72  and the connecting member  74  form a speed-reducing gear unit  49  that is connected to the input shaft  15  and that generates the reduced-speed rotation that is slower than the rotation of the input shaft  15 . The rotation control clutch C- 5  forms rotation state switching means  50  for switching the connecting member  74 , as the reduced-speed rotation output member  55 , between the reduced-speed rotation state and the free rotation state. The states of operation of the control brakes and the control clutches for the gear speeds are substantially the same as in the sixth embodiment if the rotation control clutch C- 5  is operated instead of the rotation control brake B- 2 . The speed diagram of the speed-changing dual planetary gear unit  17  is the same as in the sixth embodiment.  
         [0098]    The eighth embodiment has a construction obtained by removing the first rotation control clutch C- 4  from the construction of the fifth embodiment. Components of the eighth embodiment corresponding to those of the fifth embodiment are represented by comparable reference characters in FIG. 18, and will not be described in detail again. In this case, a carrier C 2 , as a reduced-speed rotation output member  55 , is switched between a reduced-speed rotation state in which the ring gear R 2  is connected to an input shaft  15  via a rotation control clutch C- 5  so that the carrier C 2  is rotated slower than an input shaft  15 , and a free rotation state in which the rotation control clutch C- 5  remains disengaged so that the carrier C 2  is not restricted in rotation.  
         [0099]    The speed-reducing planetary gear unit  72  forms a speed-reducing gear unit  49  that is connected to the input shaft  15  and that generates the reduced-speed rotation that is slower than the rotation of the input shaft  15 . The rotation control clutch C- 5  forms rotation state switching means  50  for switching the carrier C 2 , as the reduced-speed rotation output member  55 , between the reduced-speed rotation state and the free rotation state. The states of operation of the control clutches and the control brakes for the gear speeds are substantially the same as in the sixth embodiment if the rotation control clutch C- 5  is operated instead of the rotation control brake B- 2 . The speed diagram of the speed-changing dual planetary gear unit  17  is the same as in the sixth embodiment.  
         [0100]    Next described will be a ninth embodiment in which the speed-reducing gear unit  49  is formed by a speed-reducing gear train. The ninth embodiment is substantially the same as the first embodiment, with respect to the speed-changing dual planetary gear unit  17 , the first to third control clutches C- 1  to C- 3 , the first and second control brakes B- 3 , B- 4 , the one-way clutch F- 1 , etc., which are represented in comparable reference characters in FIG. 19, and will not be described below. A speed-reducing gear train  75  and a connection relationship between the speed-reducing gear train  75  and the speed-changing dual planetary gear unit  17  that distinguish the ninth embodiment from the first embodiment will be described. A turbine  47  of a fluid torque converter  11  is connected to an input shaft  76  that is rotatably supported by a transmission case  12  of an automatic transmission  10 . A large-diameter gear  77 , an intermediate-diameter gear  78  and a small-diameter gear  79  are fixed to the input shaft  76 . A first gear  80  that has a diameter equal to that of the large-diameter gear  77  and that meshes with the large-diameter gear  77  is rotatably supported on an axis  21  of a speed-changing dual planetary gear unit  17 . A second gear  81  and a third gear  82  that mesh with the intermediate-diameter gear  78  and the small-diameter gear  79 , respectively, are rotatably supported on the axis  21 . Therefore, the first gear  80  rotates at an input rotation equal in speed to the rotation of the input shaft  76 . The second gear  81  rotates at a first reduced-speed rotation that is slower than the rotation of the input shaft  76 . The third gear  82  rotates at a second reduced-speed rotation that is slower than the first rotation.  
         [0101]    A connecting member  83  is disposed rotatably on the axis  21 . The connecting member  83  is detachably connected to a second sun gear S 4  and a first sun gear S 3  via a first control clutch C- 1  and a third control clutch C- 3 , respectively, and is detachably connected to the second gear  81  and the third gear  82  via a first rotation control clutch C- 4  and a second rotation control clutch C- 5 , respectively. Therefore, the connecting member  83 , as a reduced-speed rotation output member  55 , is switched among a first reduced-speed rotation state in which the connecting member  83  is directly connected to the second gear  81  via the first rotation control clutch C- 4  so that the connecting member  83  is rotated at a first reduced-speed rotation that is slower than the input rotation, a second reduced-speed rotation state in which the connecting member  83  is connected to the third gear  82  via the second rotation control clutch C- 5  so that the connecting member  83  is rotated at a reduced-speed rotation that is slower than the first reduced-speed rotation, and a free rotation state in which the first and second rotation control clutches C- 4 , C- 5  remain disengaged so that the connecting member  83  is not restricted in rotation.  
         [0102]    The speed-reducing gear train  75  and the connecting member  83  form a speed-reducing gear unit  49  that is connected to the input shaft  76  and that generates the first reduced-speed rotation that is slower than the rotation of the input shaft  76  and that generates the second reduced-speed rotation that is slower than the first reduced-speed rotation. The first and second rotation control clutches C- 4 , C- 5  form rotation state switching means  50  for switching the connecting member  83  as the reduced-speed rotation output member  55  among the reduced-speed rotation states and the free rotation state. The states of operation of the control brakes and the control clutches for the gear speeds are substantially the same as in the first embodiment if the first and second rotation control clutches C- 4 , C- 5  are operated instead of the first and second rotation control brakes B- 1 , B- 2 . The speed diagram of the speed-changing dual planetary gear unit  17  is the same as in the first embodiment.  
         [0103]    In the ninth embodiment, the speed-reducing gear train  75  is formed by the large, intermediate and small-diameter gears  77 - 79  and the first to third gears  80 - 82 , the small-diameter gear  79  and the third gear  82  may be omitted as shown in FIG. 20.  
         [0104]    In a tenth embodiment, shown in FIG. 20, a first gear  80  rotates at an input rotation equal in speed to the rotation of an speed-reducing planetary gear unit  72 , and a second gear  81  rotates at a reduced-speed rotation that is slower than the input rotation. A connecting member  83  is detachably connected to first and second sun gears S 3 , S 4  via third and first control clutches C- 3 , C- 1 , and is detachably connected to the second gear  81  via a rotation control clutch C- 5 . Therefore, the connecting member  83 , as a reduced-speed rotation output member  55 , is switched between a reduced-speed rotation state in which the connecting member  83  is connected to the second gear  81  via the rotation control clutch C- 5  so that the connecting member  83  rotates at a reduced-speed rotation that is slower than the rotation of the input shaft  76 , and a free rotation state in which the rotation control clutch C- 5  remains disengaged so that the connecting member  83  is not restricted in rotation.  
         [0105]    The speed-reducing gear train  75  and the connecting member  83  form a speed-reducing gear unit  49  that is connected to the input shaft  76  and that generates an input rotation equal in speed to the rotation of the input shaft  76  and a reduced-speed rotation that is slower than the input rotation. The rotation control clutch C- 5  forms rotation state switching means  50  for switching the connecting member  83  as the reduced-speed rotation output member  55  between the reduced-speed rotation state and the free rotation state. The states of operation of the control clutches and the control brakes for the gear speeds are the same as in the sixth embodiment if the rotation control clutch C- 5  is operated instead of the rotation control brake B- 2 . The speed diagram of the speed-changing dual planetary gear unit  17  is the same as that in the sixth embodiment.  
         [0106]    Next described will be embodiments in which a single planetary gear unit identical to that in the third embodiment is used, and the speed-changing dual planetary gear unit  17  is formed by a dual planetary gear unit that is different from those of the foregoing embodiments. The speed-reducing planetary gear unit  70  is the same as that in the third embodiment, and is represented by a comparable reference character in the drawings, and will not be described below.  
         [0107]    In a speed-changing dual planetary gear unit  84  of an eleventh embodiment shown in FIG. 21, a carrier C 3  of a double-pinion type planetary gear mechanism  93  and a sun gear S 4  of a single-pinion type planetary gear mechanism  94  are connected, and a ring gear R 3  and a carrier C 4  are connected. Specifically, the speed-changing dual planetary gear unit  84  includes sun gears S 3 , S 4  rotatably supported on a common axis  13 , pinions  86  meshed with the sun gear S 3  via intermediate pinions  85 , a carrier C 3  that supports the pinions  86  and the intermediate pinions  85  and that is connected to the sun gear S 4  and is rotatably supported on the common axis  13 , a ring gear R 3  rotatably supported on the common axis  13  and meshed with the pinions  86 , pinions  87  meshed with the sun gear S 4 , a carrier C 4  that supports the pinions  87  and that is connected to the ring gear R 3  and is rotatably supported on the common axis  13 , and a ring gear R 4  rotatably supported on the common axis  13  and meshed with the pinions  87 . The ring gear R 4  is connected to an output shaft  18 . The carrier C 3  connected to the sun gear S 4  is connected with a first control brake B- 3  that selectively connects the sun gear S 4  and the carrier C 3  to a transmission case  12  so as to restrict rotation thereof. The carrier C 4  connected to the ring gear R 3  is connected with a second control brake B- 4  that selectively connects the ring gear R 3  and the carrier C 4  to the transmission case  12  so as to restrict rotation thereof.  
         [0108]    First and third control clutches C- 1 , C- 3  are provided for selectively transferring rotation of a carrier C 2  of a speed-reducing planetary gear unit  70  to the sun gear S 3  and the carrier C 3 , respectively, of the speed-changing dual planetary gear unit  84 . A second control clutch C- 2  is provided for selectively transferring rotation of an input shaft  15  to the carrier C 4 . Similarly to the third embodiment, a rotation control clutch C- 4  selectively connects the carrier C 2  of the speed-reducing planetary gear unit  70  to a ring gear R 2 , and a rotation control brake B- 2  selectively restricts rotation of a sun gear S 2 . Therefore, the carrier C 2  as a reduced-speed rotation output member  55  is switched among an input rotation state in which the carrier C 2  is connected to the ring gear R 2  via the rotation control clutch C 4  so that the carrier C 2  rotates at an input rotation equal in speed to the rotation of the input shaft  15 , a reduced-speed rotation state in which rotation of the sun gear S 2  is restricted by the rotation control brake B- 2  so that the carrier C 2  rotates at a reduced-speed rotation that is slower than the rotation of the input shaft  15 , and a free rotation state in which the rotation control clutch C- 4  and the rotation control brake B- 2  remain disengaged so that the carrier C 2  is not restricted in rotation.  
         [0109]    The eleventh embodiment constructed as described above is able to achieve gear ratios of nine forward speeds and two reverse speeds by selectively actuating the first and second control brakes B- 3 , B- 4 , the first to third control clutches C- 1  to C- 3 , the rotation control clutch C- 4  and the rotation control brake B- 2 . A speed diagram of the eleventh embodiment is shown in FIG. 22. In the eleventh embodiment, the first sun gear S 4  and the carrier C 3 , as the first element, are connected to the third control clutch C- 3  and the first control brake B- 3 ; the ring gear R 3  and the carrier C 4 , as the second element, are connected to the second control clutch C- 2  and the second control brake B- 4 ; the ring gear R 4 , as the third element, is connected to the output shaft  18 ; and the sun gear S 3 , as the fourth element, is connected to the first control clutch C- 1 . The states of operation of the control clutches and the control brakes for the gear speeds are the same as the states in the third embodiment shown in FIG. 8.  
         [0110]    In a speed-changing dual planetary gear unit  88  of a twelfth embodiment shown in FIG. 23, sun gears S 3 , S 4  of two double-pinion type planetary gear mechanisms  31 ,  32  are connected, and a ring gear R 3  and a carrier C 4  thereof are connected. Specifically, the speed-changing dual planetary gear unit  88  includes the sun gears S 3 , S 4  interconnected and rotatably supported on a common axis  13 , pinions  90  meshed with the sun gear S 3  via intermediate pinions  89 , pinions  92  meshed with the sun gear S 4  via intermediate pinions  91 , a carrier C 3  that supports the intermediate pinions  89  and the pinions  90  and that is rotatably supported on the common axis  13 , the carrier C 4  that supports the intermediate pinions  91  and the pinions  92  and that is connected to the ring gear R 3  and is rotatably supported on the common axis  13 , and a ring gear R 4  that is rotatably supported on the common axis  13  and that is meshed with the pinions  92  and is connected to the output shaft  18 . The carrier C 3  is connected with a first control brake B- 3  that selectively connects the carrier C 3  to a transmission case  12  so as to restrict rotation of the carrier C 3 . The carrier C 4  is connected with a second control brake B- 4  that selectively connects the carrier C 4  to the transmission case  12  so as to restrict rotation of the carrier C 4 . First and third control clutches C- 1 , C- 3  are provided for selectively transferring rotation of a carrier C 2  of a speed-reducing planetary gear unit  70  to the sun gear S 3  and the carrier C 3 , respectively, of the speed-changing dual planetary gear unit  88 . A second control clutch C- 2  is provided for selectively transferring rotation of an input shaft  15  to the carrier C 4  of the speed-changing dual planetary gear unit  88 . Similarly to the third embodiment, a rotation control clutch C- 4  selectively connects the carrier C 2  of the speed-reducing planetary gear unit  70  to a ring gear R 2 , and a rotation control brake B- 2  selectively restricts rotation of a sun gear S 2 . Therefore, the carrier C 2 , as a reduced-speed rotation output member  55 , is switched among an input rotation state in which the carrier C 2  is connected to the ring gear R 2  via the rotation control clutch C- 4  so that the carrier C 2  rotates at an input rotation equal in speed to the rotation of the input shaft  15 , a reduced-speed rotation state in which rotation of the sun gear S 2  is restricted by the rotation control brake B- 2  so that the carrier C 2  rotates at a reduced-speed rotation that is slower than the rotation of the input shaft  15 , and a free rotation state in which the rotation control clutch C- 4  and the rotation control brake B- 2  remain disengaged so that the carrier C 2  is not restricted in rotation.  
         [0111]    A speed diagram of the twelfth embodiment is shown in FIG. 24. In the twelfth embodiment, the carrier C 3 , as the first element, is connected to the third control clutch C- 3  and the first control brake B- 3 ; the ring gear R 3  and the carrier C 4 , as the second element, are connected to the second control clutch C- 2  and the second control brake B- 4 ; the ring gear R 4  as the third element is connected to the output shaft  18 ; and the sun gear S 3  as the fourth element is connected to the first control clutch C- 1 . The states of operation of the control clutches and the control brakes for the gear speeds are the same as the states in the third embodiment shown in FIG. 8.  
         [0112]    In a speed-changing dual planetary gear unit  95  in a thirteenth embodiment shown in FIG. 25, a sun gear S 3  of a single-pinion type planetary gear mechanism  98  and a sun gear S 4  of a double-pinion type planetary gear mechanism  99  are connected and integrated, and a carrier C 3  and a carrier C 4  thereof are connected and integrated. Specifically, the speed-changing dual planetary gear unit  95  includes the common sun gear S 3 , S 4  supported rotatably on a common axis  13 , a ring gear R 3  supported rotatably on the common axis  13  and meshed with the sun gear S 3 , S 4  via long pinions  96 , a ring gear R 4  supported rotatably on the common axis  13  and meshed with the sun gear S 3 , S 4  via the long pinions  96  and intermediate pinions  97 , and the common carrier C 3 , C 4  supporting the long pinions  96  and the intermediate pinions  97  and rotatably supported on the common axis  13 . The ring gear R 4  is connected to an output shaft  18 . The ring gear R 3  is connected with a first control brake B- 3  that selectively connects the ring gear R 3  to a transmission case  12  so as to restrict rotation of the ring gear R 3 . The carrier C 3 , C 4  is connected with a second control brake B- 4  that selectively connects the carrier C 3 , C 4  to the transmission case  12  so as to restrict rotation of the carrier C 3 , C 4 . First and third control clutches C- 1 , C- 3  are provided for selectively transferring rotation of a carrier C 2  of a speed-reducing planetary gear unit  70  to the sun gear S 3 , S 4  and to the carrier C 3 , respectively, of the speed-changing dual planetary gear unit  95 . A second control clutch C- 2  is provided for selectively transferring rotation of an input shaft  15  to the carrier C 3 , C 4  of the speed-changing dual planetary gear unit  95 . Similarly to the third embodiment, a rotation control clutch C- 4  selectively connects the carrier C 2  of the speed-reducing planetary gear unit  70  to a ring gear R 2 , and a rotation control brake B- 2  selectively restricts rotation of a sun gear S 2 . Therefore, the carrier C 2 , as a reduced-speed rotation output member  55 , is switched among an input rotation state in which the carrier C 2  is connected to the ring gear R 2  via the rotation control clutch C- 4  so that the carrier C 2  rotates at an input rotation equal in speed to the rotation of the input shaft  15 , a reduced-speed rotation state in which rotation of the sun gear S 2  is restricted by the rotation control brake B- 2  so that the carrier C 2  rotates at a reduced-speed rotation that is slower than the rotation of the input shaft  15 , and a free rotation state in which the rotation control clutch C- 4  and the rotation control brake B- 2  remain disengaged so that the carrier C 2  is not restricted in rotation.  
         [0113]    A speed diagram of the thirteenth embodiment is shown in FIG. 26. In the thirteenth embodiment, the ring gear R 3 , as the first element, is connected to the third control clutch C- 3  and the first control brake B- 3 ; the carrier C 3 , C 4 , as the second element, is connected to the second control clutch C- 2  and the second control brake B- 4 ; the ring gear R 4 , as the third element, is connected to the output shaft  18 ; and the sun gear S 3 , S 4 , as the fourth element, is connected to the first control clutch C- 1 . The states of operation of the control clutches and the control brakes for the gear speeds are the same as the states in the third embodiment shown in FIG. 8.  
         [0114]    While the invention has been described with reference to what are presently considered to be preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments or constructions. On the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single embodiment, are also within the spirit and scope of the invention.