Patent Publication Number: US-7896145-B2

Title: Automatic transmission including clutch devices

Description:
TECHNICAL FIELD 
     The present invention relates in general to an automatic transmission including clutch devices, and more particularly to an automatic transmission having a compact arrangement of the clutch devices and a reduced axial dimension. 
     BACKGROUND ART 
     There is known an automatic transmission of a type incorporating a plurality of frictional coupling devices including a plurality of clutches which have respective clutch drums for operating the clutches. For reducing the required axial dimension of the automatic transmission, one of the clutch drums is disposed within another of the clutch drums. JP-5-33833 A discloses an example of such type of automatic transmission which incorporates two clutches operable to connect one rotary member to respective two other rotary members, and in which the clutch drum of one of those two clutches is fitted in the clutch drum of the other clutch, whereby the required axial dimension of the automatic transmission can be reduced. 
     In the automatic transmission disclosed in the above-identification publication, two fluid passages through which a working fluid is supplied to advance pistons of the two clutches to force friction plates against each other are formed in the axial direction of the automatic transmission, at substantially the same radial position. Although the required axial dimension of the automatic transmission can be reduced owing to the arrangement in which one of the two clutch drums is disposed radially inwardly within the other clutch drum, the arrangement of the two fluid passages described above undesirably results in an increase of the required axial dimension of the automatic transmission, so that the automatic transmission has a comparatively large axial overall length. 
     DISCLOSURE OF THE INVENTION 
     The present invention was made in view of the background art described above. It is an object of this invention to provide an automatic transmission which includes a plurality of frictional coupling devices and which has a reduced axial dimension. 
     The object indicated above may be achieved according to the principle of the present invention, which provides an automatic transmission including a first clutch and a second clutch, comprising (a) a first drum in which a first piston of the first clutch is axially slidably received and which cooperates with the first piston to define a first oil chamber therebetween, (b) a second drum which is disposed coaxially with the first drum, so as to accommodate the first drum, and in which a second piston of the second clutch is axially slidably received, the second drum cooperating with the second piston to define a second oil chamber therebetween, (c) a first fluid supply portion for feeding a working fluid into the first oil chamber through the first drum and the second drum, to operate the first piston, and (d) a second fluid supply portion for feeding the working fluid into the second oil chamber through the second drum, to operate the second piston, and wherein the second fluid supply portion is located radially outwardly of the first fluid supply portion. 
     In the automatic transmission constructed according to the present invention as described above the second fluid supply portion is located radially outwardly of the first fluid supply portion, so that the first and second fluid supply portions do not interfere with each other in the axial direction of the automatic transmission. Accordingly, the first and second fluid supply portions  82 ,  92  can be located close to each other in the axial direction of the automatic transmission, whereby the required axial dimension of the automatic transmission can be reduced. Where the automatic transmission is installed on a front-drive vehicle of the type in which the axis of the automatic transmission extends in the transverse or lateral direction of the vehicle, in particular, the overall width of the vehicle can be reduced. 
     In one preferred form of the present invention, the second drum includes a second inner cylindrical wall and a second outer cylindrical wall which are coaxial with each other, and further includes a second bottom wall connecting the corresponding axial end portions of the second inner and outer cylindrical walls, and a second annular protrusion extending from a radially intermediate part of the second bottom wall in an axial direction thereof toward the first drum. In this form of the invention, the second inner cylindrical wall and the second annular protrusion of the second drum are rotatably supported by a housing of the automatic transmission, and the second piston is axially received in a second annular recess formed between the second annular protrusion and the second outer cylindrical wall. Further, the second oil chamber is defined by the second piston, the second outer cylindrical wall, the second bottom wall and the second annular protrusion, and the second fluid supply portion communicates with the second oil chamber through a second through-hole formed through the second annular protrusion. Accordingly, the pressurized working fluid is fed into the second oil chamber through the second through-hole formed through the second annular protrusion, so that the second piston axially slidably received in the second oil chamber is axially moved by the pressure of the working fluid introduced into the second oil chamber. 
     In one advantageous arrangement of the preferred form of the invention described above, the first drum includes a first inner cylindrical wall and a first outer cylindrical wall which are coaxial with each other, and further includes a first bottom wall connecting corresponding axial end portions of the first inner and outer cylindrical walls, and a first annular protrusion extending from a radially intermediate part of the first bottom wall in an axial direction thereof away from the second drum. In this case, the first piston is axially slidably received in a first annular recess formed between the first annular protrusion and the first outer cylindrical wall, and the first oil chamber is defined by the first piston, the first inner cylindrical wall, the first bottom wall and first annular protrusion. Further, the first fluid supply portion communicates with the first oil chamber through a first through-hole formed through the first inner cylindrical portion, and a third through-hole formed through the second inner cylindrical wall. Accordingly, the pressurized working fluid is fed into the first oil chamber through the first fluid supply portion, the first through-holes formed through the first inner cylindrical wall of the first drum, and the third through-hole formed through the second inner cylindrical wall of the second drum, so that the first piston axially slidably received in the first oil chamber is axially moved by the pressure of the working fluid introduced into the first oil chamber. 
     The first inner cylindrical wall of the first drum and the second inner cylindrical wall of the second drum may be fixed to each other so as to inhibit relative rotation of the first and second inner cylindrical walls. so that the first and third through-holes can be formed through the respective first and second inner cylindrical walls. 
     The first clutch may be provided to selectively connect a first rotary member to a second rotary member disposed coaxially with the first rotary member while the second clutch may be provided to selectively connect the first rotary member to a third rotary member disposed coaxially with said first rotary member. In this case, the first rotary member can be rotated at different speeds when the first clutch and the second clutch are selectively engaged, respectively, permitting the automatic transmission to have a relatively large number of operating positions having respective different speed ratios. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic view of an automatic transmission constructed according to one embodiment of the present invention is applicable; 
         FIG. 2  is a view indicating combinations of frictional coupling clutches placed in their engaged states to establish respective operating positions (gear positions) of the automatic transmission of  FIG. 1 ; and 
         FIG. 3  is a fragmentary elevational view in cross section of clutches devices incorporated in the automatic transmission of  FIG. 1 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring first to the schematic view of  FIG. 1 , there is shown an automatic transmission  10  of a vehicle constructed according to one embodiment of this invention. The automatic transmission  10  is disposed between an engine  8 , and drive wheels (not shown) of the vehicle, and is constructed to transmit an output of the engine  8  to the drive wheels. The vehicle has a body to which a stationary member in the form of housing  16  is fixed. Within this housing  16 , there are accommodated a torque converter  20 , an input shaft  22  connected to the torque converter  20 , a first planetary gear set  24 , a second planetary gear set  26 , and a third planetary gear set  28 , such that these major components  20 ,  22 ,  24 ,  26 ,  28  are arranged in the order of description in the left direction as seen in  FIG. 1 . The torque converter  20  is provided with a lock-up clutch  18  arranged to transmit a rotary motion of a crankshaft  12  of the engine  8  through a power transmitting medium in the form of a fluid. The automatic transmission  10  has an output shaft  30  a rotary motion of which is transmitted to the drive wheels through a counter gear (not shown). Since the automatic transmission  10  is constructed symmetrically with respect to its axis, a lower half of the automatic transmission  10  is not shown in the schematic view of  FIG. 1 . 
     The first planetary gear set  24  is of a double-pinion type including a sun gear S 1 , a plurality of pairs of mutually meshing planetary gears P 1 , a carrier CA 1  supporting the planetary gears P 1 , and a ring gear R 1  meshing with the sun gear S 1  through the planetary gears P 1 . The carrier CA 1  supports the planetary gears P 1  such that each planetary gear P 1  is rotatable about its axis and such that the planetary gears P 1  are rotatable about an axis of the automatic transmission  10 . 
     A first clutch C 1  is disposed between the carrier CA 1  of the first planetary gear set  24  and the torque converter  20 , and a first brake B 1  is disposed radially outwardly of the first clutch C 1 . Further, a second clutch C 2  is disposed radially outwardly of the ring gear R 1 , and a third clutch C 3  is disposed between the carrier CA 1  and the second planetary gear set  26 . 
     Each of the second and third planetary gear sets  26 ,  28  is of a Ravingneaux type wherein the carrier and the ring gear are formed integrally with each other. The second planetary gear set  24  is of a single-pinion type including a sun gear S 2 , a planetary gear P 2 , a carrier CA 2  and a ring gear R 2  meshing with the sun gear S 2  through the pinion gear P 2 . The carrier CA 2  supports the pinion gear P 2  such that the pinion gear P 2  is rotatable about its axis and about the axis of the automatic transmission  10 . The third planetary gear set  28  is of a double-pinion type including a sun gear S 3 , a plurality of pairs of mutually meshing pinion gears P 3 , a carrier CA 3 , and a ring gear R 3  meshing with the sun gear S 3  through the pinion gears P 3 . The carrier CA 3  supports the pinion gears P 3  such that each pinion gear P 3  is rotatable about its axis and such that the pinion gears P 3  are rotatable about the axis of the automatic transmission  10 . 
     A second brake B 2  and a one-way clutch F 1  are disposed radially outwardly of the ring gear R 2  of the second planetary gear set  26 , and a fourth clutch C 4  is disposed radially outwardly of the third planetary gear set  28 . 
     In the first planetary gear set  24 , the sun gear S 1  is fixed to the housing  16 , and is held stationary, and the carrier CA 1  is fixed directly to the input shaft  22 . Since the carrier CA 1  is fixed to a second rotary member  14  as well as the input shaft  22 , the carrier CA 1  is considered to function as the second rotary member  14 . The ring gear R 1  is always rotated at a fixed speed ratio. Since the ring gear R 1  is fixed to a third rotary member  15 , the ring gear R 1  is considered to function as the third rotary member  15 . The second rotary member  14  (carrier CA 1 ) is connectable through the first clutch C 1  to a first rotary member  13  fixed to the second sun gear S 1  of the second planetary gear set  26 , so that a rotary motion of the input shaft  22  is transmitted to the second sun gear S 2  without speed reduction while the first clutch C 1  is placed in its engaged state. The third rotary member  15  (ring gear R 1 ) is connectable through the second clutch C 2  to the first rotary member  13 , and connectable through the third clutch C 3  to the sun gear S 3  of the third planetary gear set  28 , so that a rotary motion of the ring gear R 1  rotating at the fixed speed ratio is transmitted to the sun gear S 2  while the second clutch C 2  is placed in its engaged state, and to the sun gear S 3  while the third clutch C 3  is placed in its engaged state. The first rotary member  13  can be fixed to the housing  16  and held stationary while the first brake B 1  is placed in its engaged state. 
     In the second planetary gear set  26 , the sun gear S 2  is fixed to the first planetary gear set  24 , as described above, and the carrier CA 2  is formed integrally with the carrier CA 3  of the third planetary gear set  28 . The sun gear S 2  is connectable through the fourth clutch C 4  to the input shaft  22 , and can be fixed to the housing  16  through the second brake B 2  or one-way clutch F 1 . The ring gear R 2  is formed integrally with the ring gear R 2  of the third planetary gear set  28 , and is fixed to the output shaft  30 . A rotary motion of the output shaft  30  is transmitted to the drive wheels through the counter gear described above. 
     In the third planetary gear set  28 , the sun gear S 3  is connectable through the third clutch C 3  to the ring gear R 1  of the first planetary gear set  24 , as described above. The carrier CA 3  has the same function as the carrier CA 2 , and the ring gear R 3  operates in the same manner as the ring gear R 2 . 
     The automatic transmission  10  constructed as described above is placed in a selected one of its operating positions “Rev1”, “Rev2”, “N”, “1 st ”, “2 nd ”, “3 rd ”, “4 th ”, “5 th ”, “6 th ”, “7 th ” and “8 th ”, when the corresponding one of eleven combinations of two frictional coupling devices selected from the clutches C 1 -C 4 , brakes B 1 , B 2  and one-way clutch F 1  is placed in the engaged state, as indicated in  FIG. 2 . In this figure, “O” represents the engaged state of each frictional coupling device. 
     The automatic transmission  10  is also shown in the fragmentary elevational view in cross section of  FIG. 3 , wherein “C” represents the axis of the automatic transmission  10 , the lower half of which is not shown. 
     In  FIG. 3 , the clutch C 1  is shown as a first frictional coupling device  36 , and the clutch C 2  is shown as a second frictional coupling device  38 , while the brake B 1  is shown as a third frictional coupling device  40 . 
     In the first planetary gear set  24  shown in detail in  FIG. 3 , the carrier CA 1  is fixed to a flange portion  22   a  of the input shaft  22  which is rotatably supported by bearings including thrust bearings. The flange  22   a  extends radially outwardly from the input shaft  22 , that is, perpendicularly to the axis C. The un gear S 1  is fixed to the housing  16 , and the ring gear R 1  in the form of an annular member meshing with the planetary gears P 1  has a splined outer circumferential surface to which are splined a plurality of friction plates  64  of the second frictional coupling device  38 . The ring gear R 1  is fixed to the second clutch hub  60 , so that a rotary motion of the ring gear R 1  is transmitted to the second clutch hub  60 . 
     The first frictional coupling device  36  in the form of the first clutch C 1  includes, as its major components, a first clutch hub  42 , a first drum  44 , a first piston  46  axially slidably received within the first drum  44 , a return spring  48 , and a spring seat  50  on which the return spring  48  is seated. The first clutch hub  42  receives a rotary motion of the input shaft  22  through the carrier CA 1  of the first planetary gear set  24 . The return spring  48  biases the first piston  46  toward its original axial position in an axial direction away from friction plates  62 ,  64  of the first frictional coupling device  36 . 
     The second frictional coupling device  38  in the form of the second clutch C 2  includes, as its major components, a second clutch hub  60  formed integrally and rotatable with the ring gear R 1  of the first planetary gear set  24 , a second drum  52 , a second piston  54  axially slidably received within the second drum  52 , a return spring  56 , and a spring seat  58  on which the return spring  56  is seated. The return spring  56  biases the second piston  54  toward its original axial position in the axial direction away from the friction plates  62 ,  64  of the second frictional coupling devices  38 . 
     The third frictional coupling device  40  in the form of the first brake B 1  includes, as its major components, the above-described second drum  52 , a third piston  61 , a return spring  65 , a spring seat  68  on which the return spring  65  is seated, and the housing  16 . The second drum  52  has a splined outer circumferential surface to which are splined the friction planes  64  of the third frictional coupling device  40 . 
     The first drum  44  is a double-sleeve structure which is open at one of its opposite axial ends and is closed at the other axial end. Described in detail, the first drum  44  consists of: a first inner cylindrical wall  44   a  and a first outer cylindrical wall  44   c  having a common axis aligned with the axis C; a first bottom wall  44   b  in the form of an annular disc connecting the first inner and outer cylindrical walls  44   a ,  44   c  at their corresponding axial ends; and a first annular protrusion  44   d  protruding from a radially intermediate part of the first bottom wall  44   b  in the axial direction toward the open end of the first drum  44 , namely, in the axial direction away from the second drum  52 . 
     The first inner cylindrical wall  44   a  has an inner circumferential surface having a diameter substantially equal to a diameter of an outer circumferential surface of a second inner cylindrical wall  70   a  (described below) of the second drum  52 , so that the first inner cylindrical wall  44   a  is fitted on the second inner cylindrical wall  70   a . The first outer cylindrical wall  44   a  has a splined outer circumferential surface to which the friction plates  62  of the first frictional coupling device  36  are splined at their radially outer ends. The friction plates  62  and the friction plates  64  are alternately arranged in the axial direction of the first frictional coupling device  36  such that each of the friction plates  64  is sandwiched between the adjacent two friction plates  62 . The friction plates  64  are splined at their radially inner ends to a splined outer circumferential surface of the first clutch hub  42 . This first clutch hub  42  is fixed to the carrier CA 1  of the first planetary gear set  24 , and is rotated with the carrier CA 1 . The first clutch hub  42  as well as the carrier CA 1  functions as the second rotary member  14  shown in  FIG. 1 . 
     The first piston  46  is axially slidably fitted in a first annular recess  45  formed between the first annular protrusion  44   d  and the first inner cylindrical wall  44   a  of the first drum  44 . 
     The first piston  46  includes a first inner sleeve portion  46   a  axially slidably fitted on an outer circumferential surface of the first inner cylindrical wall  44   a  of the first drum  44  through an O-ring, a first outer sleeve portion  46   c  axially sidably fitted on an outer circumferential surface of the first annular protrusion  44   d  of the first drum  44  through an O-ring, a base portion  46   b  in the form of an annular disc connecting the first inner and outer sleeve portions  46   a ,  46   c , and a presser portion  46   d  which extends radially outwardly from one axial end of the first outer sleeve portion  46   c  which is adjacent to the first annular protrusion  44   d  of the first drum  44 . The presser portion  46   d  has a distal end portion for pressing contact with the nearest friction plate  62  of the first frictional coupling device  36  to force the friction plates  62 ,  64  against each other. A first oil chamber  49  which is a pressure-tight space is defined by the first piston  46 , the first inner cylindrical wall  44 , the first bottom wall  44   b  and the first annular protrusion  44   d.    
     The second drum  52  is rotatably supported by the stationary member in the form of the housing  16 , and consists of two members in the form of an inner drum  70  and an outer drum  72  which are welded together. 
     The inner drum  70  consists of a second inner cylindrical wall  70   a  rotatably supported by the housing  16 , and a second annular protrusion  70   b  which extends from one of opposite axial end portions of the second inner cylindrical wall  70   a  that is remote from the first planetary gear set  24 . The second annular protrusion  70   b  has a cylindrical portion  67 , and an abutting portion  66  formed at one of opposite axial ends of the cylindrical portion  67 , for abutting contact with the first bottom wall  44   b  of the first drum  44 . 
     The outer drum  72  is a cylindrical member which is open at one of its opposite axial ends and which consists of a second bottom wall  72   a , and a second outer cylindrical wall  72   b . The second bottom wall  72   a  is welded to one of opposite axial end portions of the cylindrical portion  67  of the second annular protrusion  70   b  of the inner drum  70 , which one axial end portion is remote from the abutting portion  66 . The second bottom wall  72   a  extends radially outwardly of the cylindrical portion  67  of the second annular protrusion  70   b . The second outer cylindrical wall  72   b  extends from the radially outer end of the second bottom wall  72   a  in the axial direction of the automatic transmission  10 . The second drum  52  is considered to include the second inner and outer cylindrical portions  70   a ,  72   b , the second bottom wall  72   a  connecting the second inner and outer cylindrical portions  70   a ,  72   a , and the second annular protrusion  70   b  which extends from a radially intermediate part of the second bottom wall  72   a  in the axial direction toward the first drum  44 . 
     The axial open end portion of the second outer cylindrical wall  72   b  has a splined inner circumferential surface to which the friction plates  62  of the second frictional coupling device  38  are splined at their radially outer ends such that each of the other, friction plates  64  is sandwiched between the adjacent two friction plates  62 . The friction plates  64  of the second frictional coupling device  38  are splined at their radially inner ends to a splined outer circumferential surface of the ring gear R 1  of the first planetary gear set  24 . 
     The second outer cylindrical wall  72   b  has a splined outer circumferential surface to which the friction plates  62  of the third frictional coupling device  40  are splined at their radially inner ends such that each of the other friction plates  62  is sandwiched between the adjacent two friction plates  64 . The friction plates  62  of the third frictional coupling device  40  are splined at their radially outer ends to a splined inner circumferential surface of a third outer cylindrical wall  16   a  of the housing  16 . 
     The second piston  54  is axially slidably received in a second annular recess  71  formed between the second annular protrusion  70   b  and the second outer cylindrical wall  72   b.    
     The second piston  54  consists of a base portion  54   a , a sleeve portion  54   b , and a presser portion  54   c . The base portion  54   a  is axially slidably fitted through O-rings in the second annular recess  71  between the second annular protrusion  70   b  and the second outer cylindrical wall  72   b . The sleeve portion  54   b  extends from the radially outer end of the base portion  54   a  in the axial direction of the automatic transmission  10 , through an annular space formed between the first outer cylindrical wall  44   c  of the first drum  44  and the second outer cylindrical wall  72   b  of the outer drum  72  of the second drum  52 , beyond the axial open end of the first outer cylindrical wall  44   c , toward the friction plates  62 ,  64  of the second frictional coupling device  38 . The presser portion  54   c  is formed at the axial end of the sleeve portion  54   b  remote from the base portion  54   a , for pressing contact with the nearest friction plate  72  of the second frictional coupling device  38 , to force the friction plates  62 ,  64  against each other. A second oil chamber  55  which is a pressure-tight space is defined by the base portion  54   a  of the second piston  54 , the second bottom wall  72   a  and second outer cylindrical wall  72   b  of the outer drum  72 , and the second annular protrusion  70   b.    
     The third piston  61  is axially slidably received through O-rings in a space formed between the third outer cylindrical wall  16   a  and a third annular protrusion  16   b  of the housing  16 . The third piston  61  includes a presser portion  61   a  for pressing contact with the nearest friction plate  72  of the third frictional coupling device  40 , to force the friction plates  62 ,  64  against each other. The presser portion  61   a  extends through a spring seat  68  fixed to the third outer cylindrical wall  16   a , and a return spring  65  is interposed between the spring seat  68  and the third piston  61 , to bias the third piston  61  toward its original axial position in an axial direction away from friction plates  62 ,  64  of the third frictional coupling device  40 . A third oil chamber  63  which is a pressure-tight space is defined by the third piston  61 , the third outer cylindrical wall  16   a  and the third annular protrusion  16   b.    
     The spring seat  50  is a disk-shaped member is fitted between the outer circumferential surface of the second inner cylindrical wall  70   a  of the inner drum  70  and the inner circumferential surface of the first outer sleeve portion  46   c  of the first piston  46 . The above-described return spring  48  for biasing the first piston  48  in the axial direction away from the friction plates  62 ,  64  of the first frictional coupling device  36  is interposed between the spring seat  50  and the first piston  46 . The spring seat  50  is held, at its surface on the side of the second frictional coupling device  38 , in abutting contact with a retainer ring  78  fixed to the outer circumferential surface of the second inner cylindrical wall  70   a  of the inner drum  70 . The retainer ring  78  prevents an axial movement of the spring seat  50  in the axial direction away from the first piston  46 . A pressure-tight space defined by the spring seat  50 , the first piston  46 , the first inner cylindrical wall  44   a  and the second cylindrical wall  70   a  functions as a so-called “centrifugal-pressure canceling chamber”. 
     The spring seat  58  is a disk-shaped member is fitted between the outer circumferential surface of the second annular protrusion  70   b  of the inner drum  70  and the inner circumferential surface of the sleeve portion  54   b  of the second piston  54 . The above-described return spring  56  for biasing the second piston  54  in the axial direction away from the friction plates  62 ,  64  of the second frictional coupling device  38  is interposed between the spring seat  58  and the base portion  54   a  of the second piston  54 . The spring seat  58  is held, at its surface on the side of the first drum  44 , in abutting contact with a retainer ring  79  fixed to the outer circumferential surface of the second annular protrusion  70   b  of the inner drum  70 . The retainer ring  79  prevents an axial movement of the spring seat  58  in the axial direction away from the second piston  64 . A pressure-tight space defined by the spring seat  58 , the second piston  64 , the second annular protrusion  70   b  of the inner drum  70  functions as another “centrifugal-pressure canceling chamber”. 
     The housing  16  has a first fluid supply portion  82  for feeding a pressurized working fluid into the first oil chamber  49  through a first through-hole  84  formed through the first inner cylindrical wall  44   a  of the first drum  44 , and a third through-hole  86  formed through the second inner cylindrical wall  70   a  of the inner drum  70  of the second drum  52 . The housing  16  is provided with two first sealing members in the form of rings  87  located on the opposite sides of the first fluid supply portion  82  as seen in the axial direction of the automatic transmission  10 . These first sealing rings  87  prevent leakage of the working fluid from the first fluid supply portion  82 . 
     The housing  16  further has a second fluid supply portion  92  for feeding the pressurized working fluid into the second oil chamber  55  through a second through-hole  94  formed through the cylindrical portion  67  of the second annular protrusion  70   b  of the inner drum  70  of the second drum  52 . The housing  16  is provided with two second sealing members in the form of rings  95  located on the opposite sides of the second fluid supply portion  92  as seen in the axial direction of the automatic transmission  10 . These second sealing rings  95  prevent leakage of the working fluid from the second fluid supply portion  92 . 
     The cylindrical portion  67  of the second annular protrusion  70   b  of the inner drum  70 , through which the second through-hole  94  is formed in fluid communication with the second fluid supply portion  92 , has a larger diameter than the second inner cylindrical portion  70   a  of the inner drum  70 . Accordingly, the second fluid supply portion  92  is located radially outwardly of the first fluid supply portion  82 . Accordingly, one of the two first sealing rings  87  located on one side of the first fluid supply portion  82  which is nearer to the second fluid supply portion  92 , and one of the two second sealing rings  95  located on one side of the second fluid supply portion  92  which is nearer to the first fluid supply portion  82  can be located relatively close to each other in the axial direction of the automatic transmission  10 , without an interference between those two adjacent sealing rings  87 ,  95 . Therefore, the first and second fluid supply portions  82 ,  92  can be located close to each other even where the above-indicated two adjacent sealing rings  87 ,  95  are located at substantially the same axial position of the automatic transmission  10 . 
     In the present embodiment, the first drum  44  and the second drum  52  are connected to each other such that the first and second drums  44 ,  52  are axially movable relative to each other but are not rotatable relative to each other, that is, rotated together. To this end, the axial open end portion of the first inner cylindrical wall  44   a  of the first drum  44  has a splined inner circumferential surface, while the corresponding axial open end portion of the second inner cylindrical wall  70   a  of the inner drum  70  of the second drum  52  has a splined outer circumferential surface. Thus, the first inner cylindrical wall  44   a  and the second inner cylindrical wall  70   a  cooperate to have a spline-fitting portion  70  for permitting the axial relative movement of the first and second drums  44 ,  52  while inhibiting the relative rotation of these two drums  44 ,  52 . It is further noted that the abutting portion  66  of the second annular protrusion  70   b  of the inner drum  70  functions as a stopper for limiting the distance of relative axial movement of the first and second drums  44 ,  52 , by the abutting contact of the abutting portion  66  with the first bottom wall  44 . Further, the return spring  48  which is seated on the spring seat  50  and which biases the first piston  46  and first drum  44  toward the second drum  52  functions to limit the distance of the axial movements of the first and second drums  44 ,  52  toward the spring seat  50 . 
     A lubricant receiver plate  98  is interposed between the spring seat  50  and the carrier CA 1  of the first planetary gear set  24 . This lubricant receiver plate  98  also functions as a stopper for limiting the axial movement of the first and second drums  44 ,  52  as a unit. The lubricant receiver plate  98  serves to collect a lubricant and direct the collected lubricant into an oil passage  100  formed through the carrier CA 1  of the first planetary gear set  24 , for lubricating the planetary gears P of the first planetary gear set  24 . 
     There will be described an operation of the automatic transmission  10  constructed according to the present invention. 
     When the pressurized working fluid is fed into the first oil chamber  49  through the first fluid supply portion  82  of the housing  16 , the first through-hole  84  of the first inner cylindrical wall  44   a  and the third through-hole  86  of the second inner cylindrical wall  70   a , the first piston  46  is axially moved such that the base portion  46   b  is moved in the axial direction away from the first bottom wall  44   b  of the first drum  44 , so that the presser portion  46   d  is brought into abutting contact with the nearest friction plate  62  of the first frictional coupling device  36 . Since the axial movement of the friction plates  62 ,  64  of the first frictional coupling device  36  toward the axial open end of the first drum  44  is prevented by the retainer ring  78  which is located on one side of the first frictional coupling device  36  which is remove from the presser portion  46   d  and which is fixed to the inner circumferential surface of the first outer cylindrical wall  44   c  of the first drum  44 . Accordingly, the friction plates  62 ,  64  of the first frictional coupling device  36  are forced against each other by the axial movement of the presser portion  46   d  toward the retainer ring  78 . Thus, the first frictional coupling device  36  in the form of the first clutch C 1  is brought into its engaged state. 
     When the first frictional coupling device  36  is engaged by the axial movement of the first piston  46 , as described above, a rotary motion of the carrier CA 1  of the first planetary gear set  24  is transmitted to the first drum  44 , so that the second drum  52  is rotated together with the first drum  44 . It is noted that the first drum  44  and the second drum  52  cooperate to function as the first rotary member  13  of the first planetary gear set  24  including the first frictional coupling device  36  in the form of the first clutch C 1  shown in  FIG. 1 . The rotary motion of the first rotary member  13  is transmitted to the sun gear S 2  of the second planetary gear set  26 . 
     When the pressurized working fluid is fed into the second oil chamber  55  through the second fluid supply portion  92  of the housing  16  and the second through-hole  94  of the second annular protrusion  70   b  of the inner drum  70 , the second piston  54  is axially moved such that the base portion  54   a  is moved in the axial direction away from the second bottom wall  72   a  of the outer drum  72 , so that the presser portion  54   c  is brought into abutting contact with the nearest friction plate  62  of the second frictional coupling device  38 . Since the axial movement of the friction plates  62 ,  64  of the second frictional coupling device  38  toward the axial open end of the outer drum  72  is prevented by the retainer ring  96  which is located on one side of the second frictional coupling device  38  which is remove from the presser portion  54   c  and which is fixed to the inner circumferential surface of the second outer cylindrical wall  72   b  of the outer drum  72 . Accordingly, the friction plates  62 ,  64  of the second frictional coupling device  38  are forced against each other by the axial movement of the presser portion  54   c  toward the retainer ring  96 . Thus, the second frictional coupling device  38  in the form of the second clutch C 2  is brought into its engaged state. 
     When the second frictional coupling device  38  is engaged by the axial movement of the second piston  54 , as described above, a rotary motion of the ring gear R 1  of the first planetary gear set  24  is transmitted to the second drum  52 . It is noted that the ring gear R 1  functions as the third rotary member  15  of the first planetary gear set  24  including the second frictional coupling device  38  in the form of the second clutch C 2  shown in  FIG. 1 . The rotary motion of the third rotary member  15  is transmitted to the sun gear S 2  of the second planetary gear set  26 . 
     When the pressurized working fluid is fed into the third oil chamber  63  through a fluid passage not shown, the third piston  61  is axially moved toward the third frictional coupling device  40 , so that the presser portion  61   a  is brought into abutting contact with the nearest friction plate  62  of the third frictional coupling device  40 . Since the axial movement of the friction plates  62 ,  64  of the third frictional coupling device  40  toward the axial open end of the third outer cylindrical wall  16   a  of the housing  16  is prevented by a retainer ring  104  which is located on one side of the third frictional coupling device  40  which is remove from the presser portion  61   a  and which is fixed to the inner circumferential surface of the third outer cylindrical wall  16   b . Accordingly, the friction plates  62 ,  64  of the third frictional coupling device  40  are forced against each other by the axial movement of the presser portion  61   a  toward the retainer ring  104 . Thus, the third frictional coupling device  40  in the form of the first brake B 1  is brought into its engaged state. 
     When the third frictional coupling device  40  is engaged by the axial movement of the third piston  61 , as described above, rotary motions of the second drum  52  and the first drum  44  are stopped and inhibited. It is noted that the first and second drums  44 ,  52  function as the first rotary member  13  of the first planetary gear set  24  including the third frictional coupling device  40  in the form of the second clutch C 2  shown in  FIG. 1 . The rotary motion of the sun gear S 2  of the second planetary gear set  26  is stopped and inhibited. 
     In the automatic transmission  10  constructed according to the illustrated embodiment of this invention, the first fluid supply portion  82  and the second fluid supply portion  92  are located at the respective different radial positions of the automatic transmission  10 , so that the first sealing rings  87  provided for the first fluid supply portion  82  and the second sealing rings  95  provided for the second fluid supply portion  92  do not interfere with each other. Accordingly, the first and second fluid supply portions  82 ,  92  can be located close to each other in the axial direction of the automatic transmission  10 , whereby the required axial dimension of the automatic transmission  10  can be reduced. 
     The illustrated embodiment is further arranged such that the pressurized working fluid is fed into the second oil chamber  55  through the second fluid supply portion  92  and the second through-hole  94  formed through the cylindrical portion  67  of the second annular protrusion  70   b  of the inner drum  70  of the second drum  52 , so that the second piston  54  is advanced by the pressure of the working fluid introduced into the second oil chamber  55 . 
     The illustrated embodiment is also arranged such that the pressurized working fluid is fed into the first oil chamber  49  through the first fluid supply portion  82 , the first through-holes  84  formed through the first inner cylindrical wall  44   a  of the first drum  44 , and the third through-hole  86  formed through the second inner cylindrical wall  70   a  of the second drum  52 , so that the first piston  46  is advanced by the pressure of the working fluid introduced into the first oil chamber  49 . 
     The illustrated embodiment is further arranged such that the first inner cylindrical wall  44   a  of the first drum  44  and the second inner cylindrical wall  70   a  of the second drum  52  are splined to each other so as to inhibit relative rotation of those first and second inner cylindrical walls  44   a ,  70   a , so that the first and third through-holes can be formed through the respective first and second inner cylindrical walls  44   a ,  70   a.    
     The illustrated embodiment is still further arranged such that the first clutch C 1  is provided to selectively connect the mutually coaxial first and second rotary members  13 ,  14  to each other, while the second clutch C 2  is provided to selectively connect the mutually coaxial first and third rotary members  13 ,  15  to each other, so that the first rotary member  13  can be rotated at different speeds when the first clutch C 1  and the second clutch C 2  are selectively engaged, respectively, permitting the automatic transmission  10  to have a relatively large number of operating positions having respective different speed ratios. 
     While the preferred embodiment of the present invention has been described in detail by reference to the accompanying drawing, it is to be understood that the invention is not limited to the details of the illustrated embodiment, but may be otherwise embodied. 
     The automatic transmission  10  according to the illustrated embodiment is suitably used for a vehicle equipped with a transversely-mounted engine, such as an FF (front-engine front-drive) vehicle, in which the automatic transmission is installed such that the axis of the automatic transmission is parallel to the lateral or transverse direction of the vehicle. However, the automatic transmission according to the present invention may be used for a vehicle equipped with a longitudinally-mounted engine, such as an FR vehicle, in which the automatic transmission is installed such that the axis of the automatic transmission is parallel to the longitudinal direction of the vehicle. 
     It is to be understood that the present invention may be embodied with various other changes and modifications which may occur to those skilled in the art.