Patent Publication Number: US-2022235849-A1

Title: Automatic transmission

Description:
TECHNICAL FIELD 
     The present disclosure relates to an automatic transmission mounted on a vehicle. 
     BACKGROUND OF THE DISCLOSURE 
     An automatic transmission mounted on a vehicle generally includes a plurality of planetary gear mechanisms (planetary gear sets), and a plurality of friction engagement elements, such as a clutch and a brake. The automatic transmission selectively engages the plurality of friction engagement elements so as to switch a power transmission path via each planetary gear mechanism, and thus, a transmission gear stage corresponding to an operation state of the vehicle is achieved. 
     For example, JP2019-158053A discloses an automatic transmission provided with four planetary gear mechanisms and five friction engagement elements including three clutches and two brakes, and selectively engages three of the five friction engagement elements so as to achieve eight forward gear stages and one reverse gear stage. 
     JP2019-158053A discloses a brake having a fixed-side cylindrical member which is spline-coupled to a transmission case, and a rotation-side cylindrical member which is coupled to a given rotating element constituting the planetary gear mechanism. The outer circumferential side of the fixed-side cylindrical member of the brake is engaged with fixed-side friction plates having spline parts at the inner circumferential side, and the inner circumferential side of the rotation-side cylindrical member is engaged with rotation-side friction plates having spline parts at the outer circumferential side. The fixed-side friction plates and the rotation-side friction plates are alternately disposed between the fixed-side cylindrical member and the rotation-side cylindrical member. 
     Between tooth surfaces of the transmission case and the fixed-side cylindrical member which are spline-coupled to each other, a gap (backlash) for smooth meshing is provided. Therefore, after the fixed-side cylindrical member rotates about its axis with respect to the transmission case by the amount of the backlash, the tooth surface of the fixed-side cylindrical member contacts the tooth surface of the transmission case so that the rotation of the fixed-side cylindrical member is received. 
     Conventionally, since the backlash is provided at the spline-engagement part, the brake disclosed in JP2019-158053A is provided with the backlash at three points, between the rotation-side cylindrical member and the rotation-side friction plates, between the fixed-side cylindrical member and the fixed-side friction plates, and between the fixed-side cylindrical member and the transmission case. Therefore, the backlash between the fixed-side cylindrical member and the transmission case is set to be larger than those at the other parts so as to absorb backlash at the other parts. 
     However, in a case where the backlash between the fixed-side cylindrical member and the transmission case is set to be larger, when input torque is transmitted from the engine side to a drive wheel side, the backlash between the fixed-side cylindrical member and the transmission case is rapidly made smaller by the torque inputted into a ring gear. As a result, the tooth surfaces instantaneously collide with each other and teeth rattling noise may be caused. Such teeth rattling noise is also caused in a driven state where rotational force is transmitted from a drive wheel to the engine by coasting of the drive wheel. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure is made in view of the above situations, and one purpose thereof is to provide an automatic transmission provided with a brake having a fixed-side cylindrical member spline-coupled to a transmission case, and capable of reducing a teeth rattling noise between the transmission case and the fixed-side cylindrical member. 
     According to one aspect of the present disclosure, an automatic transmission is provided, which includes a brake including a fixed-side cylindrical member spline-coupled to a transmission case, a rotation-side cylindrical member coupled to a given rotating member, a plurality of friction plates disposed between the fixed-side cylindrical member and the rotation-side cylindrical member, and including a fixed-side friction plate configured to be spline-engaged with the fixed-side cylindrical member and a rotation-side friction plate configured to be spline-engaged with the rotation-side cylindrical member, and a piston configured to engage the plurality of friction plates. The automatic transmission includes a shock absorbing member disposed between a spline part of the transmission case and a spline part of the fixed-side cylindrical member and configured to absorb impact when the fixed-side cylindrical member rotates relative to the transmission case. 
     According to this configuration, the shock absorbing member is disposed between the spline parts of the transmission case and the fixed-side cylindrical member so that the impact when the fixed-side cylindrical member rotates relative to the transmission case can be absorbed. Therefore, a teeth rattling noise caused when a tooth surface of the fixed-side cylindrical member contacts a tooth surface of the transmission case can be reduced. 
     For example, when the brake is engaged in a driving state and a drive force from a driving source is transmitted to the fixed-side cylindrical member via the given rotating member, the rotation-side cylindrical member, and the plurality of friction plates, backlash between the fixed-side cylindrical member and the transmission case is rapidly made smaller by the drive force transmitted to the fixed-side cylindrical member, which causes the teeth rattling noise when the tooth surface of the fixed-side cylindrical member contacts the tooth surface of the transmission case. In this regard, by the shock absorbing member disposed between the spline parts of the transmission case and the fixed-side cylindrical member, the rotation of the fixed-side cylindrical member with respect to the transmission case can be reduced (the rotating speed is slowed down), and by the backlash between the tooth surface of the fixed-side cylindrical member and the tooth surface of the transmission case being made smaller, the teeth rattling noise is reduced. 
     A position of the fixed-side cylindrical member may be regulated in an axial direction by a fixed-side holding member fixed to the transmission case. 
     According to this configuration, the axial position of the fixed-side cylindrical member can be regulated in a configuration where the fixed-side cylindrical member is spline-coupled to the transmission case. 
     The rotation-side cylindrical member may be disposed opposing, and radially outward, of the fixed-side cylindrical member. 
     According to this configuration, compared with a case where the rotation-side cylindrical member is disposed radially inward, the centrifugal force caused by the rotation of the rotation-side cylindrical member disposed radially outward can efficiently lubricate the friction plates. 
     The shock absorbing member may include a first shock absorbing member disposed between a tooth surface of the spline part of the transmission case at a first side in a rotational direction, and a tooth surface of the spline part of the fixed-side cylindrical member at a second side in the rotational direction, and a second shock absorbing member disposed between a tooth surface of the spline part of the transmission case at the second side in the rotational direction, and a tooth surface of the spline part of the fixed-side cylindrical member at the first side in the rotational direction. 
     According to this configuration, the teeth rattling noise caused between the tooth surface of the fixed-side cylindrical member at the second rotational direction side and the tooth surface of the transmission case at the first rotational direction side can be reduced by the first shock absorbing member. The teeth rattling noise caused between the tooth surface of the fixed-side cylindrical member at the first rotational direction side and the tooth surface of the transmission case at the second rotational direction side can be reduced by the second shock absorbing member. Thus, the teeth rattling noise can be reduced both in the driving state and a driven state. 
     The first shock absorbing member may include a first spring being a coil spring, and the second shock absorbing member may include a second spring being a coil spring. A spring constant of the shock absorbing member may be set based on a net spring constant of the first spring and the second spring. 
     According to this configuration, compared with a case where the shock absorbing member is comprised of either one of the first shock absorbing member and the second shock absorbing member, the teeth rattling noise can be reduced without excessively increasing the spring constant of the first spring or the second spring. Moreover, compared with the case where only the first shock absorbing member or the second shock absorbing member is provided, in the case where the spring constant of the shock absorbing member is set based on the net spring constant of the first spring and the second spring, the spring constant of each member can be reduced, thus the assembling of the shock absorbing member being easier. 
     The shock absorbing member may be disposed in a compressed state. 
     According to this configuration, the state where the shock absorbing member is applied with load beforehand (preload) can be achieved in the neutral state where torque is not inputted into the fixed-side cylindrical member. Therefore, compared with a case where the shock absorbing member is not applied with load beforehand, the load required for rotating the fixed-side cylindrical member with respect to the transmission case is increased, and the rotation of the fixed-side cylindrical member relative to the transmission case can be reduced. 
     Further, compared with the case where the shock absorbing member is not applied with load beforehand, the rotation of the fixed-side cylindrical member with respect to the transmission case can be reduced even when larger torque is inputted into the fixed-side cylindrical member. For example, in order to increase the number of gear stages for improving fuel efficiency, when a path length of a power transmission member which couples a rotating member of a planetary gear mechanism and a friction engagement element etc. is made longer, the inertial of the power transmission member becomes larger and the torque inputted into the fixed-side cylindrical member is increased. However, since the shock absorbing member is applied with load beforehand, the rotation of the fixed-side cylindrical member with respect to the transmission case can be suppressed. 
     A spline tooth of the spline part of the transmission case may be formed such that the width in a circumferential direction becomes narrower from a first side to a second side in the axial direction. 
     According to this configuration, the interval between the adjacent spline teeth of the transmission case increases as it goes from the first axial direction side to the second axial direction side. For example, when the fixed-side cylindrical member and the shock absorbing member are assembled to the spline part of the transmission case from the second axial direction side to the first axial direction side, they can be assembled while the shock absorbing member is gradually compressed from the second axial direction side to the first axial direction side. Accordingly, compared to a case where the shock absorbing member is assembled to spline teeth with a constant width in the circumferential direction while maintaining the compressed state which is set for after assembly, the assembling can be easier. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view schematically illustrating an automatic transmission according to one embodiment of the present disclosure. 
         FIG. 2  is an engagement table for friction engagement elements of the automatic transmission. 
         FIG. 3  is a cross-sectional view of a brake of the automatic transmission, and the periphery thereof. 
         FIG. 4  is another cross-sectional view of the brake of the automatic transmission, and the periphery thereof. 
         FIG. 5  is still another cross-sectional view of the brake of the automatic transmission, and the periphery thereof. 
         FIG. 6  is a cross-sectional view of the brake of the automatic transmission and the periphery thereof, taken along a line VI-VI of  FIG. 3 . 
         FIG. 7  is an enlarged view of a part indicated by an arrow VII of  FIG. 6 . 
         FIG. 8  is a perspective view illustrating an assembled state of a first hub member and a shock absorbing member of the brake. 
         FIG. 9  is another cross-sectional view of the brake of the automatic transmission and the periphery thereof, taken along a line IX-IX of  FIG. 6 . 
         FIGS. 10A and 10B  are partial cross-sectional views schematically illustrating the brake illustrated in  FIG. 6  and a transmission case. 
         FIG. 11  is a view schematically illustrating the automatic transmission at the 1st gear. 
         FIG. 12  is a view schematically illustrating a third planetary gear set. 
         FIGS. 13A to 13C  are explanatory views of torque transmitted from a drum member to the first hub member via a friction plate. 
         FIGS. 14A to 14D  are explanatory views of assembling method of the first hub member and a first shock absorbing member of the brake. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Hereinafter, one embodiment of the present disclosure is described with reference to the accompanying drawings. 
       FIG. 1  is a view schematically illustrating an automatic transmission according to one embodiment of the present disclosure. The automatic transmission  10  is coupled to a drive source, such as an engine, without an intervention of a hydraulic power transmission, such as a torque converter. The automatic transmission  10  has an input shaft  12  which is coupled to the drive source and disposed inside a transmission case  11  at a drive source side (left side in this figure), and an output shaft  13  disposed at an anti-drive source side (right side in this figure). The automatic transmission  10  is a longitudinal type, such as for front-engine rear-drive (FR) vehicles, in which the input shaft  12  and the output shaft  13  are disposed coaxially. 
     On the axis of the input shaft  12  and the output shaft  13 , first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  (hereinafter, simply referred to as “first, second, third, and fourth gear sets”) are disposed from the drive source side. 
     Inside the transmission case  11 , a first clutch CL 1  is disposed on the drive source side of the first gear set PG 1 , a second clutch CL 2  is disposed on the drive source side of the first clutch CL 1 , and a third clutch CL 3  is disposed on the drive source side of the second clutch CL 2 . Moreover, a first brake BR 1  is disposed on the drive source side of the third clutch CL 3 , and a second brake BR 2  is disposed on the drive source side of the third gear set PG 3  and on the anti-drive source side of the second gear set PG 2 . 
     The first, second, third, and fourth gear sets PG 1 , PG 2 , PG 3 , and PG 4  are each a single-pinion type in which a pinion supported by a carrier directly meshes with a sun gear and a ring gear. The first, second, third, and fourth gear sets PG 1 , PG 2 , PG 3 , and PG 4  have, as rotating elements, sun gears S 1 , S 2 , S 3 , and S 4 , ring gears R 1 , R 2 , R 3 , and R 4 , and carriers C 1 , C 2 , C 3 , and C 4 , respectively. 
     The first gear set PG 1  is a double sun gear type in which the sun gear S 1  is divided into two in the axial direction. The sun gear S 1  has a first sun gear S 1   a  disposed at the drive source side, and a second sun gear S 1   b  disposed at the anti-drive source side. The first and second sun gears S 1   a  and S 1   b  have the same number of teeth, and mesh with the same pinions supported by the carrier C 1 . Therefore, the first and second sun gears S 1   a  and S 1   b  always carry out the same rotation. 
     In the automatic transmission  10 , the sun gear S 1  of the first gear set PG 1  (in detail, the second sun gear S 1   b ) is always coupled to the sun gear S 4  of the fourth gear set PG 4 , the ring gear R 1  of the first gear set PG 1  is always coupled to the sun gear S 2  of the second gear set PG 2 , the carrier C 2  of the second gear set PG 2  is always coupled to the carrier C 4  of the fourth gear set PG 4 , and the carrier C 3  of the third gear set PG 3  is always coupled to the ring gear R 4  of the fourth gear set PG 4 . 
     The input shaft  12  is always coupled to the carrier C 1  of the first gear set PG 1  through between the first sun gear S 1   a  and the second sun gear S 1   b , and the output shaft  13  is always coupled to the carrier C 4  of the fourth gear set PG 4 . 
     The first clutch CL 1  is disposed between the input shaft  12  and the carrier C 1  of the first gear set PG 1 , and the sun gear S 3  of the third gear set PG 3 , to engage and disengage therebetween. The second clutch CL 2  is disposed between the ring gear R 1  of the first gear set PG 1  and the sun gear S 2  of the second gear set PG 2 , and the sun gear S 3  of the third gear set PG 3 , to engage and disengage therebetween. The third clutch CL 3  is disposed between the ring gear R 2  of the second gear set PG 2  and the sun gear S 3  of the third gear set PG 3 , to engage and disengage therebetween. 
     The first brake BR 1  is disposed between the transmission case  11  and the sun gear S 1  of the first gear set PG 1  (in detail, the first sun gear S 1   a ), to engage and disengage therebetween, and the second brake BR 2  is disposed between the transmission case  11  and the ring gear R 3  of the third gear set PG 3 , to engage and disengage therebetween. 
     With the above structure, as illustrated in  FIG. 2 , the automatic transmission  10  forms the first to eighth gears in a D-range and the reverse gear in a R-range by a combination of the engagement state of the first clutch CL 1 , the second clutch CL 2 , the third clutch CL 3 , the first brake BR 1 , and the second brake BR 2 . 
     In the automatic transmission  10 , the second brake BR 2  which is engaged at the first gear stage when a vehicle starts traveling corresponds to a brake of the automatic transmission according to the present disclosure. Below, the brake BR 2  is described. 
       FIG. 3  is a cross-sectional view of the brake of the automatic transmission and its periphery,  FIG. 4  is another cross-sectional view of the brake and its periphery, and  FIGS. 5 and 6  are still other cross-sectional views of the brake and its periphery.  FIGS. 3, 4, and 5  illustrate the cross-sectional views of the brake and its periphery corresponding to the cross sections taken along lines IV-IV, and V-V in  FIG. 6 , respectively. 
     As illustrated in  FIGS. 3 to 6 , the brake BR 2  is accommodated in the transmission case  11  formed in a substantially cylindrical shape, and is disposed on the outer circumferential side of a power transmission member  14  which is coupled to the sun gear S 3  of the third gear set PG 3  and with which one of a pair of inner and outer rotating members of each of the first, second, and third clutches CL 1 , CL 2 , and CL 3  is integrated. 
     The power transmission member  14  is disposed on the outer circumferential side of a power transmission member  15  which couples the carrier C 2  of the second gear set PG 2  to the carrier C 4  of the fourth gear set PG 4 . The power transmission member  15  is disposed on the outer circumferential side of a power transmission member  16  which couples the sun gear S 1  of the first gear set PG 1  (in detail, the second sun gear S 1   b ) to the sun gear S 4  of the fourth gear set PG 4 . 
     The brake BR 2  includes a hub member  20  which is coupled to the transmission case  11 , a drum member  60  which is disposed on the anti-drive source side of the hub member  20  as a rotation-side cylindrical member, and is coupled to the ring gear R 3  of the third gear set PG 3  which is a given rotating member, a plurality of friction plates  70  which are lined up in the axial direction between the hub member  20  and the drum member  60 , and a piston  80  which is disposed on the anti-drive source side of the plurality of friction plates  70  and engages the plurality of friction plates  70 . 
     The brake BR 2  has, at radially inward of the friction plates  70 , a hydraulic chamber  90  to which hydraulic fluid for biasing the piston  80  is supplied. The hydraulic chamber  90  includes a hydraulic chamber  91  for engagement (engagement hydraulic chamber  91 ) to which hydraulic fluid for engagement which biases the piston  80  in the engaging direction is supplied, and a hydraulic chamber  92  for disengagement (disengagement hydraulic chamber  92 ) to which hydraulic fluid for disengagement which biases the piston  80  in the disengaging direction is supplied. 
     As illustrated in  FIG. 4 , the brake BR 2  has, at the radially inward of the friction plates  70 , a spring  101  which causes a biasing force in the engaging direction to act on the piston  80  as a biasing member for biasing the piston  80 . 
     As illustrated in  FIGS. 3 to 5 , the hub member  20  includes a first hub member  21  as a fixed-side cylindrical member which is spline-engaged with and coupled to the friction plates  70  and the transmission case  11 , a second hub member  31  as a fixed-side holding member, which is disposed on the drive source side of the first hub member  21  and fixed to the transmission case  11  so as to extend to radially inward of the first hub member  21 , a third hub member  41  which is coupled to the anti-drive source side of the second hub member  31  at the radially inward of the first hub member  21 , and a fourth hub member  51  which is coupled to the anti-drive source side of the third hub member  41  at the radially inward of the first hub member  21 . 
     As illustrated in  FIG. 3 , the first hub member  21  includes a vertical wall part  22  which extends in a direction perpendicular to the axial direction of the transmission case  11  and is formed in a substantially disk shape, and a cylindrical part  23  which extends substantially cylindrically to the anti-driving-source side from radially inward of the vertical wall part  22 . 
     The first hub member  21  has a spline part  24  where a spline is formed in an outer circumferential surface of the vertical wall part  22 , and the first hub member  21  is spline-coupled to the transmission case  11  by the spline part  24  being spline-engaged with a spline part  11   a  which is formed in an inner circumferential surface of the transmission case  11 . Between the first hub member  21  and the transmission case  11 , a gap (backlash) G for smooth meshing is formed (see  FIG. 7 ). The coupling between the spline part  24  of the first hub member  21  and the spline part  11   a  of the transmission case  11  will be described later in detail. 
     The cylindrical part  23  of the first hub member  21  has a spline part  25  where a spline is formed in an outer circumferential surface, and the spline part  25  is spline-engaged with fixed-side friction plates  71  which constitute the friction plates  70 . Between the spline part  25  of the first hub member  21  and the fixed-side friction plates  71 , backlash g 2  for smooth meshing is provided (see  FIG. 7 ). The second hub member  31  includes a vertical wall part  32  which extends in a direction perpendicular to the axial direction of the transmission case  11  and is formed in a substantially disk shape. The vertical wall part  32  of the second hub member  31  is formed with a lubrication oil supply passage (not illustrated) for supplying hydraulic fluid for lubrication to the friction plates  70 . 
     As illustrated in  FIG. 4 , the second hub member  31  is formed, at a part radially outward of the vertical wall part  32 , with a through-hole  32   b  thorough which a bolt B 1  for fixing the second hub member  31  to the transmission case  11  is inserted. At an inner circumferential side of the transmission case  11 , a bolt hole  17  to be threadedly engaged with the bolt B 1  is formed at a position corresponding to the through-hole  32   b  of the vertical wall part  32 . The second hub member  31  is fixed and coupled to the transmission case  11  by using the bolt B 1 . The vertical wall part  32  of the second hub member  31  is formed with a plurality of thorough-holes  35  penetrating the vertical wall part  32  in the axial direction at the inner circumferential side. The plurality of thorough-holes  35  are provided dispersedly in the circumferential direction. 
     As illustrated in  FIG. 6 , below the transmission case  11 , a valve body  5  which supplies hydraulic fluid to the hydraulic chamber  90  and the friction plates  70  of the brake BR 2  is disposed. The valve body  5  is fixed to the transmission case  11  by being accommodated in an oil pan (not illustrated) attached below the transmission case  11 . The second hub member  31  has a valve body connecting part  34  for connecting to the valve body  5 , and it is formed so that the lubrication oil supply passage, an engagement oil supply passage which supplies hydraulic fluid for engagement to the engagement hydraulic chamber  91 , and a disengagement oil supply passage which supplies hydraulic fluid for disengagement to the disengagement hydraulic chamber  92 , are connected to the valve body  5  through a case opening  11   c  formed in the transmission case  11 . 
     As illustrated in  FIG. 3 , on the anti-driving-source side of the vertical wall part  32  of the second hub member  31 , a stepped part  32   a  which is dented to the driving-source side is formed. The stepped part  32   a  of the second hub member  31  is formed so as to engage with the inner circumferential side of the vertical wall part  22  of the first hub member  21 , when the vertical wall part  32  of the second hub member  31  contacts the vertical wall part  22  of the first hub member  21 . 
     As illustrated in  FIG. 3 , the third hub member  41  is provided with a vertical wall part  42  which extends in a direction perpendicular to the axial direction of the transmission case  11  and is formed in a substantially disk shape, a first cylindrical part  43  which extends substantially cylindrically to the anti-drive source side from radially outward of the vertical wall part  42 , and a second cylindrical part  44  which extends substantially cylindrically to the anti-drive source side from radially inward of the vertical wall part  42 . The first cylindrical part  43  and the second cylindrical part  44  are formed to have the substantially same length in the axial direction. 
     The first cylindrical part  43  of the third hub member  41  is provided at radially inward of the cylindrical part  23  of the first hub member  21 . The first cylindrical part  43  of the third hub member  41  is provided with a flange part  43   a  at the anti-drive source side, which extends radially outwardly so as to contact the inner circumferential surface of the cylindrical part  23  of the first hub member  21 . An oil supply passage L 1  for lubrication is formed between the first cylindrical part  43  of the third hub member  41  and the cylindrical part  23  of the first hub member  21 . 
     The second cylindrical part  44  of the third hub member  41  has an outer circumferential surface  44   a  at the drive source side, and an outer circumferential surface  44   b  at the anti-drive source side. The outer circumferential surface  44   b  at the anti-drive source side is formed to be smaller in a radial dimension compared with the outer circumferential surface  44   a  at the drive source side so as to form the disengagement hydraulic chamber  92 . 
     Moreover, as illustrated in  FIGS. 4 and 5 , a threaded hole  44   c  to be engaged with a bolt B 2  from the driving-source side, and a threaded hole  44   d  to be engaged with a bolt B 3  from the anti-driving-source side, are formed in the second cylindrical part  44  of the third hub member  41 . 
     The fourth hub member  51  is disposed on the anti-drive source side of the third hub member  41  so as to extend in a direction perpendicular to the axial direction of the transmission case  11  and be formed in a substantially disk shape. A plurality of through-holes  52  penetrating in the axial direction are formed at the radially inward of the fourth hub member  51 . 
     The bolt B 2  is threadedly engaged with the threaded hole  44   c  of the third hub member  41  from the drive source side through the through-hole  35  of the second hub member  31 , and the bolt B 3  is threadedly engaged with the threaded hole  44   d  of the third hub member  41  from the anti-drive source side through the through-holes  52  of the fourth hub member  51 . Accordingly, the third hub member  41  is coupled to the anti-drive source side of the second hub member  31 , and the fourth hub member  51  is coupled to the anti-drive source side of the third hub member  41 . 
     The fourth hub member  51  is formed to extend radially outward of the second cylindrical part  44  of the third hub member  41 , and an outer circumferential surface of the fourth hub member  51  is fitted to the piston  80 . 
     In the hub member  20 , the first hub member  21 , the second hub member  31 , the third hub member  41 , and the fourth hub member  51  are made of the same aluminum-based material. 
     The drum member  60  includes a cylindrical part  61  which is disposed opposing the outer circumferential side of the cylindrical part  23  of the first hub member  21 , and extends substantially cylindrically in the axial direction, and a vertical wall part which extends radially inwardly from the anti-drive source side of the cylindrical part  61  in a direction perpendicular to the axial direction of the transmission case  11 , and is formed in a substantially disk shape. 
     The vertical wall part of the drum member  60  is coupled to the ring gear R 3  as a rotating member. The cylindrical part  61  of the drum member  60  has a spline part  61   a  where spline is formed on the inner circumferential surface, and the spline part  61   a  is spline-engaged with rotation-side friction plates  72  which constitute the friction plates  70 . Between the spline part  61   a  of the drum member  60  and the rotation-side friction plates  72 , backlash g 1  for smooth meshing is provided (see  FIG. 7 ). The fixed-side friction plates  71  and the rotation-side friction plates  72  are disposed alternately in the axial direction. 
     The piston  80  is disposed between the hub member  20  and the drum member  60  (in detail, between the cylindrical part  23  of the first hub member  21  and the cylindrical part  61  of the drum member  60 ), and is slidably fitted onto the outer circumferential surface of the second cylindrical part  44  of the third hub member  41 . 
     The piston  80  is formed annularly, and includes, as illustrated in  FIG. 3 , a pressing part  81  which is provided at the outer circumferential side and presses the friction plates  70 , a hydraulic chamber forming part  82  which is provided at the inner circumferential side and forms the hydraulic chamber  90 , and a coupling part  83  which couples the pressing part  81  to the hydraulic chamber forming part  82 . 
     The pressing part  81  of the piston  80  is disposed on the anti-drive source side of the friction plates  70 , the hydraulic chamber forming part  82  is disposed radially inward of the friction plates  70 , and the coupling part  83  extends to the radially inward of the friction plates  70  from the anti-drive source side of the friction plates  70  so that it couples the pressing part  81  to the hydraulic chamber forming part  82 . 
     The hydraulic chamber forming part  82  extends to the drive source side from an inner-end part of the coupling part  83 , and extends radially inwardly from an end part at the driving-source side so as to be fitted to the outer circumferential surface  44   a  of the second cylindrical part  44  of the third hub member  41 . In this manner, the engagement hydraulic chamber  91  is formed by a space defined by the hydraulic chamber forming part  82 , the third hub member  41 , and the fourth hub member  51 . The disengagement hydraulic chamber  92  is formed by a space defined by the hydraulic chamber forming part  82  and the third hub member  41 . 
     As illustrated in  FIG. 4 , the spring  101  is disposed inside the engagement hydraulic chamber  91 . The hydraulic chamber forming part  82  which forms the engagement hydraulic chamber  91  receives, at the anti-drive source side, biasing force from the spring  101 . The spring  101 , and the engagement hydraulic chamber  91  and the disengagement hydraulic chamber  92  are disposed at positions overlapping with each other in the radial direction at the radially inward of the plurality of friction plates  70 . 
       FIG. 6  is a cross-sectional view of the brake BR 2  and the transmission case  11 , taken along a line VI-VI of  FIG. 3 .  FIG. 8  is a perspective view illustrating a state where a shock absorbing member is assembled to the first hub member  21 . 
     As illustrated in  FIG. 6 , on the inner circumferential surface of the transmission case  11 , the spline part  11   a  having a plurality of spline teeth  11   d  which are engaged with the spline part  24  of the first hub member  21  is formed. The plurality of spline teeth  11   d  are disposed in an upper range Z 1  located at the upper side of the transmission case  11 , a first-side range Z 2  on a first side of the upper range Z 1  in the rotational direction, and a second-side range Z 3  on a second side of the upper range Z 1  in the rotational direction. 
     The inner circumferential surface of the transmission case  11  is further provided with first and second shock-absorbing-member accommodating spaces A 1  and A 2  in which first and second damper spline teeth  26  and  27  for damping of the first hub member  21  (described later) and first and second shock absorbing members  210  and  220  are accommodated, respectively. 
     The first shock-absorbing-member accommodating space A 1  is disposed on a first side of the upper end part of the transmission case  11  in the rotational direction (first rotational direction side), and the second shock-absorbing-member accommodating space A 2  disposed on a second side in the rotational direction (second rotational direction side). The first shock-absorbing-member accommodating space A 1  is provided between the upper range Z 1  and the first-side range Z 2 , and the second shock-absorbing-member accommodating space A 2  is provided between the upper range Z 1  and the second-side range Z 3 . 
     The first shock-absorbing-member accommodating space A 1  is defined by a spline tooth  11   e  located at the first rotational direction side (i.e., rearward in the rotational direction in the driving state) at most among the spline teeth  11   d  in the upper range Z 1 , and a spline tooth  11   f  located at the second rotational direction side (i.e., forward in the rotational direction in the driving state) at most among the spline teeth  11   d  in the first-side range Z 2 . The second shock-absorbing-member accommodating space A 2  is defined by a spline tooth  11   g  located at the second rotational direction side at most among the spline teeth  11   d  in the upper range Z 1 , and a spline tooth  11   h  located at the first rotational direction side at most among the spline teeth  11   d  in the second-side range Z 3 . 
     The plurality of spline teeth  11   d  are engaged with a plurality of spline teeth  28  of the first hub member  21  other than the damper spline teeth  26  and  27  (described later), and the shock-absorbing-member accommodating spaces A 1  and A 2  accommodate the shock absorbing members  210  and  220 , and the damper spline teeth  26  and  27  of the first hub member  21 , respectively. 
     As illustrated in  FIGS. 6 and 8 , the first hub member  21  is provided with the spline part  24  which extends to the anti-drive source side from the outer circumferential side of the vertical wall part  22 . The spline part  24  includes the damper spline teeth  26  and  27  to which a shock absorbing member  200  (the shock absorbing members  210  and  220 ) which absorbs an impact when the first hub member  21  rotates relative to the transmission case  11  and collides against it is attached, and the plurality of spline teeth  28  formed to be shorter in the circumferential direction compared with the damper spline teeth  26  and  27 . 
     As illustrated in  FIG. 6 , the plurality of spline teeth  28  are engaged with the plurality of spline teeth  11   d  of the transmission case  11 , respectively. As illustrated in  FIG. 7 , the gap (backlash) G for smooth meshing is provided between the spline tooth  11   d  and the spline tooth  28 . The backlash G is provided between a tooth surface  28   a  at the first rotational direction side of the spline tooth  28  disposed between adjacent spline teeth  11   d , and a tooth surface  11   k  at the second rotational direction side of the spline tooth  11   d  opposing to the tooth surface  28   a , and between a tooth surface  28   b  at the second rotational direction side of the spline tooth  28 , and a tooth surface  11   m  at the first rotational direction side of the spline tooth  11   d  opposing to the tooth surface  28   b.    
     As illustrated in  FIG. 6 , the first damper spline tooth  26  is disposed in the first shock-absorbing-member accommodating space A 1  of the transmission case  11 , and the second damper spline tooth  27  is disposed in the second shock-absorbing-member accommodating space A 2 . The shock absorbing member  210  is attached to the first damper spline tooth  26 , and the second shock absorbing member  220  is attached to the second damper spline tooth  27 . 
     A first notch  29   a  is formed between the first damper spline tooth  26  of the first hub member  21  and the spline tooth  28  which is engaged with the second rotational direction side of the spline tooth  11   e  of the transmission case  11 , and a second notch  29   b  is formed between the second damper spline tooth  27  of the first hub member  21  and the spline tooth  28  which is engaged with the first rotational direction side of the spline tooth  11   g  of the transmission case  11  (see  FIG. 8 ). 
     As illustrated in  FIG. 8 , the second damper spline tooth  27  is formed in a stepped shape such that it is longer in the axial length from the second side to the first side in the rotational direction. The second damper spline tooth  27  is formed in the stepped shape by an attached part  27   a  which is located at the first rotational direction side and has the axial length for attaching the second shock absorbing member  220  thereto, an engaging part  27   b  which is located at the side of the spline tooth  11   h  of the transmission case  11  to be engaged with the spline tooth  11   h , and has the substantially same axial length as the spline tooth  28 , and a coupling part  27   c  which couples the attached part  27   a  to the engaging part  27   b  and has the axial length shorter than the attached part  27   a  and longer than the engaging part  27   b . The attached part  27   a  is formed projecting mostly toward the anti-drive source side. 
     Similar to the second damper spline tooth  27 , the first damper spline tooth  26  is formed in a stepped shape. As illustrated in  FIG. 9 , the first damper spline tooth  26  is formed in the stepped shape such that it is longer in the axial length from the first side to the second side in the rotational direction. The first damper spline tooth  26  is formed in the stepped shape by an attached part  26   a  which is located at the second rotational direction side and has the axial length for attaching the first shock absorbing member  210  thereto, an engaging part  26   b  which is located at the side of the spline tooth  11   f  of the transmission case  11  to be engaged with the spline tooth  11   f , and has the substantially same axial length as the spline tooth  28 , and a coupling part  26   c  which couples the attached part  26   a  to the engaging part  26   b  and has the axial length shorter than the attached part  26   a  and longer than the engaging part  26   b . The attached part  26   a  is formed most projectingly to the anti-drive source side. 
     In the first notch  29   a , the first shock absorbing member  210  and the spine tooth  11   e  of the transmission case  11  are arranged in the circumferential direction from the first side to the second side in the rotational direction. In the second notch  29   b , the second shock absorbing member  220  and the spline tooth  11   g  of the transmission case  11  are arranged in the circumferential direction from the second side to the first side in the rotational direction (see  FIG. 6 ). 
     As illustrated in  FIGS. 8 and 9 , the first shock absorbing member  210  is disposed between a tooth surface  26   d  of the first damper spline tooth  26  at the second rotational direction side, and a tooth surface  11   i  of the spline tooth  11   e  of the transmission case  11  at the first rotational direction side. The first shock absorbing member  210  is provided with a first spring  211  which causes a biasing force F 1  to act on the first hub member  21  toward the first rotational direction side (see  FIG. 6 ). 
     The first shock absorbing member  210  includes a plurality of first springs  211  each comprised of a coil spring extending in the circumferential direction, and arranged in the axial direction, a hub-side holding plate  212  which is made of a plate member extending in the axial direction and holds end parts of the plurality of first springs  211  at the first rotational direction side, and a case-side holding plate  215  which holds end parts of the plurality of first springs  211  at the second rotational direction side. 
     The hub-side holding plate  212  is provided with a plurality of spring guide parts  213  which cylindrically project toward the second rotational direction side, and to which the plurality of first springs  211  are attached. The case-side holding plate  215  is provided with a plurality of spring guide parts  213  which oppose to the spring guide parts  213  attached to the hub-side holding plate  212  and cylindrically project toward the first rotational direction side, and to which the plurality of first springs  211  are attached. The plurality of first springs  211  are disposed at positions overlapping with each other in the axial direction and the radial direction. 
     The first shock absorbing member  210  is attached to the first hub member  21  in a state where the hub-side holding plate  212  is supported by the tooth surface  26   d  of the first damper spline tooth  26  at the second rotational direction side, and the case-side holding plate  215  is supported by the tooth surface  11   i  of the spline tooth  11   e  of the transmission case  11  at the first rotational direction side. 
     The first shock absorbing member  210  is disposed between the first damper spline tooth  26  and the tooth surface  11   i  of the spline tooth  11   e  of the transmission case  11 , while the plurality of first springs  211  are compressed. 
     In a state where the first shock absorbing member  210  is attached to the first damper spline tooth  26  of the first hub member  21  and before the first hub member  21  is assembled to the transmission case  11 , the first springs  211  have the equilibrium length. The circumferential length of the first shock absorbing member  210  is set to be longer than the length obtained by subtracting the circumferential length of the first damper spline tooth  26  from the circumferential length of the first shock-absorbing-member accommodating space A 1 . Therefore, when the first hub member  21  is assembled to the transmission case  11 , the plurality of first springs  211  are held while being compressed in the circumferential direction. The first springs  211  are held while load is applied thereto in advance. 
     As illustrated in  FIG. 9 , the hub-side holding plate  212  is provided with an extending part  214  which extends toward the first rotational direction side from an end part of the hub-side holding plate  212  at the drive source side, and contacts a drive source side surface of the spline tooth  26  provided to the vertical wall part  22  of the first hub member  21 . A pin member (not illustrated) is projected from a driving-source-side surface of the vertical wall part  22  of the first hub member  21 , and the extending part  214  is formed with a through-hole (not illustrated) penetrating in the axial direction so that the pin member is inserted therein, and thus, the first shock absorbing member  210  is held by the first hub member  21 . 
     The case-side holding plate  215  includes a stopper part  216  which extends toward the first rotational direction side from an end part of the case-side holding plate  215  at the drive source side, and contacts an anti-drive source side surface of the spline tooth  26  provided to the vertical wall part  32  of the second hub member  31 , and an inclined part  217  which extends from an end part of the case-side holding plate  215  at the anti-drive source side, toward the anti-drive source side while inclining toward the first rotational direction side. 
     As illustrated in  FIGS. 6 and 8 , the second shock absorbing member  220  is disposed between a tooth surface  27   d  of the second damper spline tooth  27  at the first rotational direction side, and a tooth surface  11   j  at the second rotational direction side of the spline tooth  11   g  disposed on the second rotational direction side of the upper range Z 1 . The second shock absorbing member  220  is provided with a second spring  221  which causes a biasing force F 2  to act on the first hub member  21  toward the second rotational direction side (see  FIG. 6 ). 
     The second shock absorbing member  220  includes a plurality of second springs  221  each comprised of a coil spring extending in the circumferential direction, and arranged in the axial direction, a hub-side holding plate  222  which is made of a plate member extending in the axial direction and holds end parts of the plurality of second springs  221  at the second rotational direction side, and a case-side holding plate  225  which holds end parts of the plurality of second springs  221  at the first rotational direction side. 
     The hub-side holding plate  222  is provided with a plurality of spring guide parts (not illustrated) which cylindrically project to the first rotational direction side, and to which the plurality of second springs  221  are attached. The case-side holding plate  225  is provided with a plurality of spring guide parts (not illustrated) which oppose to the spring guide parts attached to the hub-side holding plate  222  and cylindrically project toward the second rotational direction side, and to which the plurality of second springs  221  are attached. The plurality of second springs  221  are disposed at positions overlapping with each other in the axial direction and the radial direction. 
     The second shock absorbing member  220  is attached to the first hub member  21  in a state where the hub-side holding plate  222  is supported by the tooth surface  27   d  of the second damper spline tooth  27  at the first rotational direction side, and the case-side holding plate  225  is supported by the tooth surface  11   j  of the spline tooth  11   g  of the transmission case  11  at the second rotational direction side. 
     The second shock absorbing member  220  is disposed between the second damper spline tooth  27  and the tooth surface  11   j  of the spline tooth  11   g  of the transmission case  11 , while the plurality of second springs  221  are compressed. 
     In a state where the second shock absorbing member  220  is attached to the second damper spline tooth  27  of the first hub member  21 , and before the first hub member  21  is assembled to the transmission case  11 , the second springs  221  have the equilibrium length. The circumferential length of the second shock absorbing member  220  is set to be longer than the length obtained by subtracting the circumferential length of the second damper spline tooth  27  from the circumferential length of the second shock-absorbing-member accommodating space A 2 . Therefore, when the first hub member  21  is assembled to the transmission case  11 , the plurality of second springs  221  are held while being compressed in the circumferential direction. The second springs  221  are held while load is applied thereto in advance. 
     The hub-side holding plate  222  is provided with an extending part  224  which extends toward the second rotational direction side from an end part of the hub-side holding plate  222  at the drive source side, and contacts a drive source side surface of the spline tooth  27  provided to the vertical wall part  22  of the first hub member  21 . A pin member (not illustrated) is projected from a drive source-side surface of the vertical wall part  22  of the first hub member  21 , and the extending part  224  is formed with a through-hole (not illustrated) penetrating in the axial direction so that the pin member is inserted therein, and thus, the second shock absorbing member  220  is held by the first hub member  21 . 
     The case-side holding plate  225  includes a stopper part  226  which extends to the second rotational direction side from an end part of the case-side holding plate  225  at the driving-source side, and contacts an anti-drive source side surface of the spline tooth  27  provided to the vertical wall part  32  of the second hub member  31 , and an inclined part  227  which extends from an end part of the case-side holding plate  225  at the anti-drive source side, to the anti-drive source side while inclining to the second rotational direction side. 
       FIGS. 10A and 10B  are partial cross-sectional views schematically illustrating the brake BR 2  and the transmission case  11  illustrated in  FIG. 6 . Operations of the first spring  211  and the second spring  221  are described with reference to  FIGS. 10A and 10B . 
     The first hub member  21  receives the biasing force F 1  to the first rotational direction side by the first shock absorbing member  210 , and receives the biasing force F 2  to the second rotational direction side by the second shock absorbing member  220 , in the state where the first hub member  21  is assembled to the transmission case  11 . 
     As illustrated in  FIG. 10A , spring constants and compression allowances for the first spring  211  and the second spring  221  are set such that, when the first hub member  21  is at a neutral position where torque is not acted thereon, the biasing force F 1  of the first shock absorbing member  210  and the biasing force F 2  of the second shock absorbing member  220 , which act on the first hub member  21 , cancel out each other. For example, since the number and the spring constant are set to be the same between the first springs  211  and the second springs  221 , they have the same compression allowance at the neutral position where the torque is not acted on the first hub member  21 . Suppose that, at the neutral position, the first rotational direction side is a negative direction, the second rotational direction side is a positive direction, the biasing force F 1  of the first spring  211  is −500 N, the biasing force F 2  of the second spring  221  is +500 N, and the spring constants of the first spring and the second spring are each 100 N/mm, the net force of the first spring  211  and the second spring  221  (F 1 +F 2 ) which acts on the first hub member  21  is balanced, thus being 0 N. 
     At the neutral position where torque is not acted on the first hub member  21 , the backlash G is provided between the tooth surface  28   a  at the first rotational direction side of the spline tooth  28  disposed between adjacent spline teeth  11   d , and the tooth surface  11   k  at the second rotational direction side of the spline tooth  11   d  opposing to the tooth surface  28   a , and between the tooth surface  28   b  at the second rotational direction side of the spline tooth  28 , and the tooth surface  11   m  at the first rotational direction side of the spline tooth  11   d  opposing to the tooth surface  28   b.    
     When torque is acted on the first hub member  21 , and the first hub member  21  rotates to the first rotational direction side (negative direction), as illustrated in  FIG. 10B , the load applied to the first spring  211  decreases whereas the load applied to the second spring  221  increases. For example, when the biasing force F 1  of the first spring  211  is −400 N and the biasing force F 2  of the second spring  221  is +600 N, the net force of the first spring  211  and the second spring  221  (F 1 +F 2 ) which acts on the first hub member  21  becomes +200 N. Therefore, by the shock absorbing member  200 , the first hub member  21  is applied with a load resisting the torque for rotating the first hub member  21  in the negative direction, and thus, the rotation of the first hub member  21  with respect to the transmission case  11  can be suppressed. 
     When the torque is acted on the first hub member  21 , and the first hub member  21  rotates to the first rotational direction side (negative direction), the backlash G between the tooth surface  28   a  at the first rotational direction side of the spline tooth  28  disposed between the adjacent spline teeth  11   d , and the tooth surface  11   k  at the second rotational direction side of the spline tooth  11   d  opposing to the tooth surface  28   a  is eliminated, and the backlash G is provided only between the tooth surface  28   b  at the second rotational direction side of the spline tooth  28 , and the tooth surface  11   m  at the first rotational direction side of the spline tooth  11   d  opposing to the tooth surface  28   b.    
     Note that, here, although the case where the first hub member  21  rotates to the first rotational direction side (negative direction) is described, also in the case where the first hub member  21  rotates to the second rotational direction side (positive direction), the load can similarly be applied by the shock absorbing member  200  in the opposite direction from the rotational direction of the first hub member  21  relative to the transmission case  11 . Therefore, the rotation of the first hub member  21  with respect to the transmission case  11  can be suppressed. 
     Next, teeth rattling noise caused between the spline part  11   a  of the transmission case  11  and the spline part  24  of the first hub member  21  is described with reference to  FIGS. 11, 12 , and  13 A to  13 C.  FIG. 12  is a view schematically illustrating a cross section of the third planetary gear set PG 3  in the axial direction, and  FIGS. 13A to 13C  are cross-sectional views schematically illustrating the brake BR 2  and the transmission case  11  in the axial direction. 
     As illustrated in  FIG. 11 , at the first gear of the automatic transmission  10 , the first brake BR 1 , the second brake BR 2 , and the first clutch CL 1  are engaged. At the first gear, the third planetary gear set PG 3  receives input torque from the engine side by the sun gear S 3 . Since the brake is engaged, the ring gear R 3  coupled to the rotation-side cylindrical member is fixed, and the input torque from the engine is transmitted to a drive wheel from the carrier C 3  via the fourth planetary gear set PG 4 , while receiving reaction force of the ring gear R 3  from the sun gear S 3 . 
     As illustrated in  FIG. 12 , in the third planetary gear set PG 3 , a tooth surface S 31  at the second rotational direction side (forward) of the sun gear S 3  which is rotated by receiving the input from the engine, contacts a tooth surface C 32  at the first rotational direction side (rearward) of a pinion gear C 30  which is located between tooth surfaces of the sun gear S 3  and coupled to the carrier C 3 , and thus, the pinion gear C 30  is rotated. The rotation of the pinion gear C 30  is transmitted to the ring gear R 3  by a tooth surface C 31  at the rearward rotational direction of the tooth of the pinion gear C 30  which is located between the tooth surfaces of the ring gear R 3  contacting a tooth surface R 31  of the ring gear R 3  at the forward rotational direction. 
     Although the rotation transmitted to the ring gear R 3  attempts to rotate the drum member  60  connected to the ring gear R 3 , since the brake BR 2  is engaged, the rotation of the drum member  60  is received by the transmission case  11  via the fixed-side friction plates  71 , the rotation-side friction plates  72 , and the first hub member  21 . 
     As illustrated in  FIG. 13A , the rotation transmitted to the drum member  60  is transmitted to the rotation-side friction plate  72  by the drum member  60  being rotated in a direction in which the gap (backlash) between a tooth surface of the drum member  60  at the first rotational direction side (rearward) and a tooth surface of the rotation-side friction plate  72  at the second rotational direction side (forward) becomes smaller, and the tooth surface of the drum member  60  contacting the tooth surface of the rotation-side friction plate  72 . 
     As illustrated in  FIG. 13B , the rotation transmitted to the rotation-side friction plate  72  is transmitted to the fixed-side friction plate  71  which rotates integrally with the rotation-side friction plate  72 , and then transmitted to the first hub member  21  by the fixed-side friction plate  71  being rotated in a direction in which the gap (backlash) between a tooth surface of the fixed-side friction plate  71  at the first rotational direction side and a tooth surface of the cylindrical part  23  of the first hub member  21  at the second rotational direction side becomes smaller, and the tooth surface of the fixed-side friction plate  71  contacting the tooth surface of the cylindrical part  23 . 
     As illustrated in  FIG. 13C , the rotation transmitted to the first hub member  21  is received by the first hub member  21  being rotated in a direction in which the gap (backlash) between a tooth surface of the spline part  24  of the first hub member  21  at the first rotational direction side and a tooth surface of the spline part  11   a  of the transmission case  11  at the second rotational direction side is reduced, and the tooth surface of the spline part  24  contacting the tooth surface of the spline part  11   a  of the transmission case  11 . 
     As described above, teeth rattling noise caused upon the reduction in the backlash between the tooth surfaces of the drum member  60  and the rotation-side friction plate  72  is absorbed by the rotation of the rotation-side friction plate  72  and the fixed-side friction plate  71 , and teeth rattling noise caused upon the reduction in the backlash between the fixed-side friction plate  71  and the cylindrical part  23  of the first hub member  21  is absorbed by the rotation of the first hub member  21 . 
     On the other hand, the rotation of the first hub member  21  is received by the transmission case  11  which does not rotate, and thus, between the tooth surfaces of the first hub member  21  and the transmission case  11 , teeth rattling noise larger than other parts is caused. 
     The backlash G between the tooth surfaces of the first hub member  21  and the transmission case  11  is set to be larger than other parts so as to absorb the backlashes g 1  and g 2  at other parts (see  FIG. 7 ). Therefore, when the input torque is to be transmitted from the engine to the drive wheel, the backlash G is rapidly made smaller by the torque inputted into the ring gear R 3 , and the tooth surface  28   a  of the first hub member  21  at the first rotational direction side and the tooth surface  11   k  of the transmission case  11  at the second rotational direction side instantaneously collide with each other, which causes the teeth rattling noise. 
     According to the automatic transmission of this embodiment, since the shock absorbing member  200  is disposed between the spline part  11   a  of the transmission case  11  and the spline part  24  of the first hub member  21 , the impact when the first hub member  21  rotates relative to the transmission case  11  and collides against it, can be reduced. As a result, the teeth rattling noise upon the contact between the tooth surface of the first hub member  21  and the tooth surface of the transmission case  11  can be reduced. 
     For example, while the brake BR 2  is engaged and the input torque from the engine is transmitted to the first hub member  21  via the sun gear S 3 , the drum member  60 , and the plurality of friction plates  70 , when the first hub member  21  is rotated to the first rotational direction side (negative direction) by the drive force transmitted to the first hub member  21 , as illustrated in  FIG. 10B , the load applied to the first spring  211  decreases whereas the load applied to the second spring  221  increases. Therefore, the first hub member  21  is applied with the load which resists the torque for rotating the first hub member  21  in the negative direction, and thus, the rotation of the first hub member  21  with respect to the transmission case  11  can be reduced, and the teeth rattling noise between the first hub member  21  and the transmission case  11  can be reduced. 
     The teeth rattling noise between the first hub member  21  and the transmission case  11  is likely to occur, for example, during switching between a driving state and a driven state of the engine (in detail, a case of using engine braking during the traveling, or re-acceleration after the engine braking). In the driving state, an accelerator pedal is depressed and a vehicle travels while drive force of the engine is transmitted to the drive wheel, and in the driven state, the accelerator pedal is not depressed and the rotating force is transmitted from the drive wheel to the engine by coasting of the drive wheel. 
     When the driving and driven states are switched, the state as illustrated in  FIG. 12 , where the tooth surface S 31  at the forward rotational direction of the sun gear S 3  which is rotated by the engine contacts the tooth surface C 32  of the pinion gear C 30  at the rearward rotational direction, and the tooth surface C 31  of the pinion gear C 30  at the rearward rotational direction contacts the tooth surface R 31  of the ring gear R 3  at the forward rotational direction, becomes a state where a tooth surface C 33  at the forward rotational direction of a tooth of the pinion gear C 30  located between the tooth surfaces of the ring gear R 3  contacts a tooth surface R 32  of the ring gear R 3  at the rearward rotational direction. 
     Here, since the contacting tooth surface is switched from the tooth surface R 31  at the forward rotational direction to the tooth surface R 32  at the rearward rotational direction, when the torque is transmitted to the drum member  60  coupled to the ring gear R 3 , the tooth surface to which torque is transmitted is switched between the state where the tooth surface  28   a  of the first hub member  21  at the rearward rotational direction contacts the tooth surface  11   k  of the transmission case  11  at the forward rotational direction, and the state where the tooth surface  28   b  of the first hub member  21  at the forward rotational direction contacts the tooth surface  11   m  of the transmission case  11  at the rearward rotational direction. 
     When the tooth surface which transmits the torque is switched, the state is changed from the state as illustrated in  FIG. 10B , where the backlash between the tooth surface  28   a  at the rearward rotational direction of the spline tooth  28  disposed between the adjacent spline teeth  11   d , and the tooth surface  11   k  at the forward rotational direction of the spline tooth  11   d  opposing to the tooth surface  28   a  is eliminated, and the backlash between the tooth surface  28   b  at the forward rotational direction of the spline tooth  28 , and the tooth surface  11   m  at the rearward rotational direction of the spline tooth  11   d  opposing to the tooth surface  28   b  becomes the maximum, to a state where the tooth surface  28   b  of the spline tooth  28  is in contact with the tooth surface  11   m  of the spline tooth  11   d . Therefore, the teeth rattling noise upon the collision between the tooth surfaces is likely to be louder. 
     In this respect, the automatic transmission  10  of this embodiment is provided with the first shock absorbing member  210  disposed between the tooth surface  26   d  of the spline part  24  of the first hub member  21  at the forward rotational direction in the driving state, and the tooth surface  11   i  of the spline part  11   a  of the transmission case  11  at the rearward rotational direction in the driving state, and the second shock absorbing member  220  disposed between the tooth surface  27   d  of the spline part  24  of the first hub member  21  at the rearward rotational direction in the driving state, and the tooth surface  11   j  of the spline part  11   a  of the transmission case  11  at the forward rotational direction in the driving state. Therefore, the teeth rattling noise caused upon the change in the tooth surface which receives torque (e.g., upon the switching between the driving and driven states, which is likely to increase backlash), can be reduced. 
     The spring constant of the shock absorbing member  200  is set based on the net spring constant of the first spring  211  and the second spring  221 . Therefore, compared with a case where the shock absorbing member  200  is comprised of either one of the first shock absorbing member  210  and the second shock absorbing member  220 , the teeth rattling noise can be reduced without excessively increasing the spring constant of the first shock absorbing member  210  or the second shock absorbing member  220 . Moreover, compared with the case where only the first shock absorbing member  210  or the second shock absorbing member  220  is provided, the spring constant of each of the first shock absorbing member  210  and the second shock absorbing member  220  can be reduced, thus the assembling of the shock absorbing member  200  being easier. 
     Since the shock absorbing member  200  is disposed in the compressed state, the state where the shock absorbing member  200  is applied with load beforehand (preload) can be achieved in the neutral state where the torque is not inputted into the first hub member  21 . Therefore, compared with a case where the shock absorbing member  200  is not applied with load beforehand, the load required for rotating the first hub member  21  with respect to the transmission case  11  is increased, and the rotation of the first hub member  21  relative to the transmission case  11  can be reduced. 
     Further, compared with the case where the shock absorbing member  200  is not applied with load beforehand, the rotation of the first hub member  21  with respect to the transmission case  11  can be reduced even when larger torque is inputted into the first hub member  21 . For example, like the automatic transmission  10  of this embodiment, when a path length of the power transmission member  14  which couples the sun gear S 3  and the first clutch CL 1  is made longer in order to increase the number of gear stages for improving fuel efficiency, the inertia of the power transmission member  14  becomes larger and the torque inputted into the first hub member  21  is increased. However, since the shock absorbing member  200  is applied with load beforehand, the rotation of the first hub member  21  with respect to the transmission case  11  can be suppressed. 
     Since the position of the first hub member  21  in the axial direction is regulated by the second hub member  31  fixed to the transmission case  11 , the structure where the first hub member  21  is spline-coupled to the transmission case  11  is easily achieved. 
     The drum member  60  is disposed opposing, and radially outward of, the first hub member  21 . Therefore, compared with a case where the drum member  60  is disposed radially inward, the centrifugal force caused by the rotation of the drum member  60  disposed radially outward can efficiently lubricate the friction plates  70 . 
       FIGS. 14A to 14D  illustrate a method of assembling the first hub member  21  to the transmission case  11 . As illustrated in  FIGS. 14A to 14D , the first hub member  21  is attached to the transmission case  11  from the drive source side to the anti-drive source side while the first damper spline tooth  26  holds the first shock absorbing member  210 . 
     The transmission case  11  is made of casting removed or pulled out from a mold from an anti-drive source side (a first axial direction side) to the drive source side (a second axial direction side), and a draft angle is provided to the spline part  11   a  of the transmission case  11 . The transmission case  11  is formed such that an interval (gap) between the adjacent spline teeth  11   d  increases from the first axial direction side to the second axial direction side. Note that in this embodiment a draft angle α provided to the spline teeth  11   d  of the transmission case  11  is 1° with respect to a line segment L along the axial line. 
     Therefore, when the first hub member  21  and the first shock absorbing member  210  are assembled to the spline part  11   a  of the transmission case  11  from the second axial direction side to the first axial direction side, they can be assembled while the first shock absorbing member  210  is gradually compressed from the second axial direction side to the first axial direction side. Accordingly, compared to a case where the shock absorbing member is assembled to a spline tooth with a constant width in the circumferential direction while maintaining the compressed state which is set for after assembly, the assembling can be easier. 
     For example, as illustrated in  FIG. 14A , before the first spring  211  is assembled to the transmission case  11 , it is held in the equilibrium length, and thus, the total length of the first damper spline tooth  26  and the first shock absorbing member  210  in the circumferential direction is longer than the length of the first shock-absorbing-member accommodating space A 1  in the circumferential direction. 
     As illustrated in  FIG. 14B , when the first hub member  21  is moved from the drive source side to the anti-drive source side so as to be assembled to the transmission case  11 , the inclined part  217  of the case-side holding plate  215  first contacts the spline tooth  11   e  of the transmission case  11 . 
     As illustrated in  FIG. 14C , when the first hub member  21  is inserted along the inclined part  217 , the first hub member  21  is moved to the anti-drive source side while the first spring  211  is compressed. As described above, since the spline tooth  11   d  is formed such that its width in the circumferential direction becomes narrower to the drive source side, the first hub member  21  is assembled while the compression allowance of the first spring  211  increases from the drive source side to the anti-drive source side. 
     As illustrated in  FIG. 14D , when the first hub member  21  and the first spring  211  are assembled to the transmission case  11 , the first spring  211  is assembled while being compressed and applied with load beforehand. Since the draft a is formed in the spline tooth  11   d  of the transmission case  11 , in the state where the first hub member  21  and the first spring  211  are assembled to the transmission case  11 , the biasing force of the first spring  211  generates force which acts on the first hub member  21  and the first spring  211  to come out from the transmission case  11  to the drive source side. With respect to this, the draft is set to be smaller than a given value (e.g., 1°) such that the force caused by the draft a to act on the first hub member  21  in the axial direction becomes smaller than a friction force between the first hub member  21  and the tooth surface of the transmission case  11 . 
     The present disclosure is not limited to the embodiment described above, but various improvement and changes in design are possible without departing from the spirit of the present disclosure. 
     For example, although in this embodiment the shock absorbing member  200  includes the first shock absorbing member  210  and the second shock absorbing member  220 , either one of the first shock absorbing member  210  and the second shock absorbing member  220  may be provided. In this case, the spring constant of the shock absorbing member may be increased compared with the case where both of the first shock absorbing member  210  and the second shock absorbing member  220  are provided. 
     Moreover, in this embodiment, the first shock absorbing member  210  and the second shock absorbing member  220  are disposed in the first shock-absorbing-member accommodating space A 1  and the second shock-absorbing-member accommodating space A 2 , respectively. However, for example, the first shock absorbing member  210  and the second shock absorbing member  220  may be disposed in the first shock-absorbing-member accommodating space A 1 , as long as the first shock absorbing member  210  and the second shock absorbing member  220  are disposed between the tooth surface of the spline part of the transmission case  11  at the second rotational direction side, and the tooth surface of the spline part of the first hub member at the first rotational direction side, and between the tooth surface of the spline part of the transmission case  11  at the first rotational direction side, and the tooth surface of the spline part of the first hub member at the second rotational direction side, respectively. 
     As described above, according to the present disclosure, an automatic transmission provided with a brake having a fixed-side cylindrical member to be spline-coupled to a transmission case, can reduce teeth rattling noise between the transmission case and the fixed-side cylindrical member. Therefore, the present disclosure may be suitably used in a technical field of manufacturing this type of automatic transmission or a vehicle mounting the automatic transmission thereon. 
     It should be understood that the embodiments herein are illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof, are therefore intended to be embraced by the claims. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
         
           
               10  Automatic Transmission 
               11  Transmission Case 
               11   i  Tooth Surface of Transmission Case at First Rotational Direction Side 
               11   j  Tooth Surface of Transmission Case at Second Rotational Direction Side 
               21  First Hub Member (Fixed-side Cylindrical Member) 
               26   d  Tooth Surface of Fixed-Side Cylindrical Member at Second Rotational Direction Side 
               27   d  Tooth Surface of Fixed-Side Cylindrical Member at First Rotational Direction Side 
               11   a ,  24  Spline Part 
               31  Second Hub Member (Fixed-side Holding Member) 
               61  Drum Member (Rotation-side Cylindrical Member) 
               70  Plurality of Friction Plates 
               71  Fixed-side Friction Plate 
               72  Rotation-side Friction Plate 
               80  Piston 
               200  Shock Absorbing Member 
               210  First Shock Absorbing Member 
               211  First Spring 
               220  Second Shock Absorbing Member 
               221  Second Spring 
             BR 2  Brake 
             R 3  Ring Gear (Given Rotating Member)