Patent Publication Number: US-2016230874-A1

Title: Power transmission device

Description:
BACKGROUND 
     The present disclosure relates to a power transmission device including a transmission, a transmission case that accommodates the transmission, and a counter drive gear to which power from the transmission is transmitted. 
     A power transmission device that is conventionally known as this type of power transmission device includes: a speed change mechanism having a Ravigneaux type planetary gear set, a multi-plate friction brake that holds a carrier of the planetary gear set stationary to a transmission case such that the carrier cannot rotate, and a one-way clutch that allows the carrier to rotate only in one direction; a counter drive gear to which power from the speed change mechanism is transmitted; and a center support including a cylindrical boss portion that rotatably supports the counter drive gear and a wall portion that is extended outward in the radial direction from one end of the boss portion and that has its outer periphery fastened to the transmission case (see, e.g., Japanese Patent Application Publication No. 2002-349683). In this power transmission device, the counter drive gear is rotatably supported by the boss portion of the center support so as to be located between the wall portion of the center support and the planetary gear set. The brake and the one-way clutch are disposed outside the planetary gear set, and a plurality of friction engagement plates of the brake and the outer periphery of the one-way clutch are fitted in splines formed in the inner peripheral surface of the transmission case. 
     Another power transmission device that is known as this type of power transmission device includes a multi-plate friction brake that holds one of rotary elements of an automatic transmission stationary to a transmission case accommodating the automatic transmission such that this rotary element cannot rotate, and this power transmission device uses a part of the transmission case also as a brake drum of the brake (see, e.g., Japanese Patent Application Publication No. 2004-36887). In this power transmission device, an oil passage through which coolant is supplied to the brake is formed in the part of the transmission case which is used also as the brake drum. 
     SUMMARY 
     In such conventional power transmission devices, it is necessary to ensure that the center support rotatably supporting the counter drive gear is strong enough to restrain occurrence of noise or vibration. However, if the thickness of the center support is increased or a rib is added in order to secure the strength, an increase in size of the power transmission device cannot be restrained. 
     The present disclosure according to an exemplary aspect more satisfactorily improves strength of a support member rotatably supporting a counter drive gear to which power from a transmission is transmitted, while restraining an increase in size of a power transmission device. 
     According to an exemplary aspect the present disclosure, a power transmission device includes a transmission, a transmission case that accommodates the transmission, a counter drive gear to which power from the transmission is transmitted, a brake that holds one of rotary elements of the transmission stationary to the transmission case such that the rotary element cannot rotate; and a support member that includes a cylindrical boss portion rotatably supporting the counter drive gear, a wall portion extended outward in a radial direction of the transmission from one end of the boss portion, and a cylindrical drum portion extended in the same direction as that of the boss portion and in an axial direction of the transmission from the wall portion and functioning as a brake drum of the brake, and that is fixed to the transmission case, wherein the boss portion, the wall portion, and the drum portion are formed integrally. 
     This power transmission device includes the brake that holds one of the rotary elements of the transmission stationary to the transmission case such that the rotary element cannot rotate, and the support member that rotatably supports the counter drive gear and that is fixed to the transmission case. This support member includes the cylindrical boss portion rotatably supporting the counter drive gear, the wall portion extended outward in the radial direction of the transmission from one end of the boss portion, and the cylindrical drum portion extended in the same direction as that of the boss portion and in the axial direction of the transmission from the wall portion and functioning as the brake drum of the brake. The support member thus functions as the brake drum of the brake, which eliminates the need to provide a portion functioning as the brake drum in other components of the power transmission device such as the transmission case. Since the boss portion, the wall portion, and the drum portion of the support member are formed integrally, the drum portion also functions as a rib. Strength of the support member can therefore be satisfactorily improved. Accordingly, in this power transmission device, an increase in size of the power transmission device can be restrained, and the strength of the support member that rotatably supports the counter drive gear to which power from the transmission is transmitted can be more satisfactorily improved. 
     The power transmission device may further include: a second brake that holds a second rotary element of the transmission, which is different from the one rotary element, stationary to the transmission case such that the second rotary element cannot rotate. The support member may further include a cylindrical second drum portion extended in an opposite direction to that of the boss portion and the drum portion and in the axial direction from the wall portion and functioning as a brake drum of the second brake, and the second drum portion may be formed integrally with the boss portion, the wall portion, and the drum portion. The support member thus has a function as the brake drum of the second brake. This eliminates the need to provide a portion functioning as the brake drum of the second brake in other components of the power transmission device such as the transmission case. Since the second drum portion is formed integrally with the boss portion, the wall portion, and the drum portion, the second drum portion also functions as a rib. This can restrain an increase in size of the power transmission device and can more satisfactorily improve the strength of the support member. 
     Moreover, the drum portion and the second drum portion may be extended in opposite directions to each other from substantially the same position in the radial direction in an outer periphery of the wall portion. 
     In addition, the brake may have a plurality of friction engagement plates that are fitted in splines formed in an inner peripheral surface of the drum portion, and a lubricating oil supply path through which lubricating oil is supplied to the plurality of friction engagement plates may be formed in the support member. A sufficient amount of lubricating oil can thus be supplied to the plurality of friction engagement plates of the brake via the lubricating oil supply path, and the plurality of friction engagement plates can be more satisfactorily lubricated and cooled. As a result, slip engagement of the brake can be effectively used in a wide range, whereby shift speeds can be smoothly formed by engaging or disengaging the brake, and a feeling of torque transmission can further be improved. 
     Moreover, the transmission case may include a case portion that accommodates at least the one rotary element. The support member may be fixed to the case portion such that the drum portion is fitted in the case portion. The lubricating oil supply path may include an oil passage that is defined by a recess formed in at least one of an inner peripheral surface of the case portion and an outer peripheral surface of the drum portion, and a plurality of through holes that communicate with the oil passage and that extend in the radial direction. At least a part of the plurality of friction engagement plates may be fitted in the drum portion so as to be located inside the recess. Since the support member is fixed to the case portion such that the drum portion is fitted in the case portion, the support member can be more firmly fixed to the transmission case. Since the oil passage forming the lubricating oil supply path is defined by the recess formed in at least one of the inner peripheral surface of the case portion and the outer peripheral surface of the drum portion, this can restrain an increase in thickness of the case portion and the drum portion associated with formation of the lubricating oil supply path. Moreover, since at least a part of the plurality of friction engagement plates is fitted in the drum portion so as to be located inside the recess, lubricating oil can be uniformly supplied to the friction engagement plates via the recess and the plurality of through holes. 
     The brake may include a piston that together with the transmission case defines an engagement oil chamber and that presses the plurality of friction engagement plates according to an oil pressure supplied to the engagement oil chamber, and a plurality of return springs that bias the piston such that the piston is separated from the plurality of friction engagement plates. The plurality of return springs may be disposed between a tip end of the drum portion and the piston. The plurality of return springs can thus be disposed without interfering with the splines of the drum portion in which the plurality of friction engagement plates are fitted. Accordingly, the plurality of return springs can be arranged at regular intervals in a circumferential direction of the piston, and a biasing force of the plurality of return springs can be uniformly applied to the piston. This restrains tilting of the piston and allows the piston to press the plurality of friction engagement plates such that the plurality of friction engagement plates are not tilted. The brake can thus be slip-engaged more accurately. 
     The brake may be engaged when the transmission forms a starting speed. Accordingly, slip engagement of the brake is effectively used when the starting speed is formed. The starting speed can thus be smoothly formed, and a feeling of torque transmission can further be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration diagram of a power transmission device according to an embodiment of the present disclosure. 
         FIG. 2  is an operation table showing the relationship between each shift speed of an automatic transmission included in the power transmission device of  FIG. 1  and the operating state of clutches and brakes. 
         FIG. 3  is an enlarged partial sectional view of a main part of the power transmission device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A mode for carrying out the present disclosure will be described with reference to the accompanying drawings. 
       FIG. 1  is a schematic configuration diagram of a power transmission device  20  according to an embodiment of the present disclosure. The power transmission device  20  shown in the figure is connected to a crankshaft of an engine, not shown, which is mounted on a front-wheel drive vehicle, and can transmit power from the engine to left and right driving wheels (front wheels), not shown. As shown in the figure, the power transmission device  20  includes a transmission case  22 , and a staring device (hydraulic transmission device)  23 , an oil pump  24 , an automatic transmission  25 , a gear mechanism (gear train)  40 , a differential gear (differential mechanism)  50 , etc. which are accommodated in the transmission case  22 . 
     The starting device  23  included in the power transmission device  20  is configured as a torque converter having an input-side pump impeller  23   p  that is connected to the crankshaft of the engine, an output-side turbine runner  23   t  that is connected to an input shaft (input member)  26  of the automatic transmission  25 , a stator  23   s  that is disposed inside the pump impeller  23   p  and the turbine runner  23   t  to adjust the flow of hydraulic oil from the turbine runner  23   t  to the pump impeller  23   p , a one-way clutch  23   o  that allows the stator  23   s  to rotate only in one direction, a lockup clutch  23   c , a damper mechanism  23   d , etc. The starting device  23  may be configured as a fluid coupling that does not have the stator  23   s.    
     The oil pump  24  is configured as a gear pump having a pump assembly including a pump body and a pump cover, an external gear connected to the pump impeller  23   p  of the starting device  23  via a hub, an internal gear meshing with the external gear, etc. The oil pump  24  is driven by the power from the engine to suction hydraulic oil (ATF) accumulated in an oil pan, not shown, to pressure-feed the suctioned hydraulic oil to a hydraulic control device, not shown, which generates an oil pressure required by the starting device  23  or the automatic transmission  25 . 
     The automatic transmission  25  is configured as an eight-speed transmission. As shown in  FIG. 1 , the automatic transmission  25  includes, in addition to the input shaft  26 , a double-pinion type first planetary gear mechanism  30 , a Ravigneaux type second planetary gear mechanism  35 , four clutches C 1 , C 2 , C 3 , C 4  that change a power transmission path from the input side to the output side, and two brakes B 1 , B 2 . 
     The first planetary gear mechanism  30  of the automatic transmission  25  has a sun gear  31  as an external gear, a ring gear  32  as an internal gear that is disposed concentrically with the sun gear  31 , and a planetary carrier  34  that holds a plurality of pairs of pinion gears  33   a ,  33   b  such that the pinion gears  33   a ,  33   b  can rotate (turn) and revolve. Each pair of pinion gears  33   a ,  33   b  mesh with each other, one of each pair of pinion gears  33   a ,  33   b  meshes with the sun gear  31 , and the other pinion gear meshes with the ring gear  32 . As shown in the figure, the sun gear  31  of the first planetary gear mechanism  30  is fixed to the transmission case  22 , and the planetary carrier  34  of the first planetary gear mechanism  30  is coupled to the input shaft  26  such that the planetary carrier  34  can rotate together with the input shaft  26 . The first planetary gear mechanism  30  is configured as what is called a reduction gear. The first planetary gear mechanism  30  reduces the rotational speed of the power transmitted to the planetary carrier  34  as an input element, and outputs the resultant power from the ring gear  32  as an output element. 
     The second planetary gear mechanism  35  of the automatic transmission  25  has a first sun gear  36   a  and a second sun gear  36   b  as external gears, a ring gear  37  as an internal gear that is disposed concentrically with the first and second sun gears  36   a ,  36   b , a plurality of short pinion gears  38   a  that mesh with the first sun gear  36   a , a plurality of long pinion gears  38   b  that mesh with the second sun gear  36   b  and the plurality of short pinion gears  38   a  and mesh with the ring gear  37 , and a planetary carrier  39  that holds the plurality of short pinion gears  38   a  and the plurality of long pinion gears  38   b  such that the plurality of short pinion gears  38   a  and the plurality of long pinion gears  38   b  can rotate (turn) and revolve. The ring gear  37  of the second planetary gear mechanism  35  functions as an output member of the automatic transmission  25 , and the power transmitted from the input shaft  26  to the ring gear  37  is transmitted to the left and right driving wheels via the gear mechanism  40 , the differential gear  50 , and drive shafts  51 . 
     The clutch C 1  is a multi-plate friction hydraulic clutch (friction engagement element) that has a hydraulic servo formed by a piston, a plurality of friction plates and separator plates, an oil chamber to which hydraulic oil is supplied, etc. and that can connect and disconnect the ring gear  32  of the first planetary gear mechanism  30  to and from the first sun gear  36   a  of the second planetary gear mechanism  35 . The clutch C 2  is a multi-plate friction hydraulic clutch that has a hydraulic servo formed by a piston, a plurality of friction plates and separator plates, an oil chamber to which hydraulic oil is supplied, etc. and that can connect and disconnect the input shaft  26  to and from the planetary carrier  39  of the second planetary gear mechanism  35 . The clutch C 3  is a multi-plate friction hydraulic clutch that has a hydraulic servo formed by a piston, a plurality of friction plates and separator plates, an oil chamber to which hydraulic oil is supplied, etc. and that can connect and disconnect the ring gear  32  of the first planetary gear mechanism  30  to and from the second sun gear  36   b  of the second planetary gear mechanism  35 . The clutch C 4  is a multi-plate friction hydraulic clutch that has a hydraulic servo formed by a piston, a plurality of friction plates and separator plates, an oil chamber to which hydraulic oil is supplied, etc. and that can connect and disconnect the planetary carrier  34  of the first planetary gear mechanism  30  to and from the second sun gear  36   b  of the second planetary gear mechanism  35 . 
     The brake B 1  is a multi-plate friction hydraulic brake that has a hydraulic servo formed by a plurality of friction plates and separator plates, an oil chamber to which hydraulic oil is supplied, etc., that can hold the second sun gear  36   b  of the second planetary gear mechanism  35  stationary to the transmission case  22  such that the second sun gear  36   b  cannot rotate, and that can release the second sun gear  36   b  from the transmission case  22 . The brake B 2  is a multi-plate friction hydraulic clutch that has a hydraulic servo formed by a plurality of friction plates and separator plates, an oil chamber to which hydraulic oil is supplied, etc., that can hold the planetary carrier  39  of the second planetary gear mechanism  35  stationary to the transmission case  22  such that the planetary carrier  39  cannot rotate, and that can release the planetary carrier  39  from the transmission case  22 . 
     The clutches C 1  to C 4  and the brakes B 1 , B 2  operate according to supply and discharge of hydraulic oil by the hydraulic control device.  FIG. 2  is an operation table showing the relationship between each shift speed of the automatic transmission  25  and the operating state of the clutches C 1  to C 4  and the brakes B 1 , B 2 . The automatic transmission  25  provides first to eighth forward speeds and first and second reverse speeds by switching the clutches C 1  to C 4  and the brakes B 1 , B 2  to the states shown in the operation table of  FIG. 2 . At least one of the clutches C 1  to C 4  may be a meshing engagement element such as a dog clutch. 
     The gear mechanism  40  has a counter drive gear  41  that is coupled to the ring gear  37  of the second planetary gear mechanism  35  of the automatic transmission  25 , a counter driven gear  43  that is fixed to a counter shaft  42  extending parallel to the input shaft  26  of the automatic transmission  25  and that meshes with the counter drive gear  41 , a drive pinion gear (final drive gear)  44  that is formed integrally with (or fixed to) the counter shaft  42  so as to be separated from the counter driven gear  43  in the axial direction, and a differential ring gear (final driven gear)  45  that meshes with the drive pinion gear  44  and that is coupled to the differential gear  50 . 
     The configuration around the counter drive gear  41  of the gear mechanism  40  and the brake B 2  of the automatic transmission  25  will be described below with reference to  FIG. 3 . 
     As shown in the figure, the counter drive gear  41  of the gear mechanism  40  which is coupled to the ring gear  37  of the second planetary gear mechanism  35  is rotatably supported by a support member (center support)  100  that is fixed to the transmission case  22  via a plurality of bolts  99 . The support member  100  includes a cylindrical boss portion  101  that rotatably supports the counter drive gear  41  via a bearing  90 , a substantially disc-shaped wall portion  102  extended outward in the radial direction of the input shaft  26  (the automatic transmission  25 ) (hereinafter simply referred to as the “radial direction”) from one end of the boss portion  101 , and an outer tube portion  110  extended in the axial direction of the input shaft  26  (the automatic transmission  25 ) (hereinafter simply referred to as the “axial direction”) from the wall portion  102 . 
     The boss portion  101  of the support member  100  is formed in a cylindrical shape and has a central hole through which the input shaft  26  etc. are inserted. As shown in  FIG. 3 , the wall portion  102  is extended outward in the radial direction from the opposite end of the boss portion  101  from the second planetary gear mechanism  35  and extends between the boss portion  101  and the outer tube portion  110 . A plurality of lightening holes  102   o  are formed in the wall portion  102  in order to reduce the weight of the support member  100 . The outer tube portion  110  includes a first drum portion  111  that is extended in the same direction as that of the boss portion  101  (to the second planetary gear mechanism  35  side) and in the axial direction from the outer periphery of the wall portion  102 , and a second drum portion  112  that is extended in the opposite direction to that of the boss portion  101  and the first drum portion  111  (to the opposite side from the second planetary gear mechanism  35 ) and in the axial direction from the outer periphery of the wall portion  102 . That is, the first and second drum portions  111 ,  112  are extended in the opposite directions to each other from substantially the same position in the radial direction in the outer periphery of the wall portion  102 . The first and second drum portions  111 ,  112  may be extended from the wall portion  102  such that their positions in the radial direction are slightly offset form each other. 
     The outer tube portion  110  (the first and second drum portions  111 ,  112 ) has an outer peripheral surface  110   s  in the form of a cylindrical surface, and a plurality of fastening portions  113  having bolt holes through which the bolts  99  are inserted are extended outward in the radial direction from the outer peripheral surface  110   s  of a substantially middle part in the axial direction of the first drum portion  111 . A projecting portion  114  is formed so as to project from the outer peripheral surface  110   s  of a substantially middle part in the axial direction of the outer tube portion  110  of the support member  100  toward the hydraulic control device, not shown, which is disposed outside the transmission case  22 . The projecting portion  114  is offset in the circumferential direction so as not to overlap the plurality of fastening portions  113  in the axial direction, and is extended from the outer peripheral surface  110   s  of the outer tube portion  110  so as to contact an inner wall of the transmission case  22 . In the present embodiment, the hydraulic control device, not shown, is attached to a side part of the transmission case  22 . The first drum portion  111  of the outer tube portion  110  includes a cutout portion, not shown, which is formed so as to avoid interference with a meshing portion between the counter drive gear  41  and the counter driven gear  43 . 
     The transmission case  22  to which the support member  100  is fixed includes a rear cover  221  that accommodates the second planetary gear mechanism  35 , the brake B 2 , the clutch C 2 , etc. The first drum portion  111  of the support member  100  is fitted in a wall portion  221   b  extending in the axial direction from an end face  221   a  on the first planetary gear mechanism  30  side of the rear cover  221  such that a stepped part  111   a  formed in the outer periphery of the first drum portion  111  contacts the end face  221   a  of the rear cover  221 . The support member  100  is fastened (fixed) to the rear cover  221  by the bolts  99  inserted through the bolt holes of the plurality of fastening portions  113  such that the first drum portion  111  is fitted in the wall portion  221   b  of the rear cover  221 . The support member  100  can thus be stably and firmly fixed to the rear cover  221  (the transmission case  22 ), so that the support member  100  is not subjected to excessive stress. 
     As shown in  FIG. 3 , the inner periphery of the first drum portion  111  of the support member  100  having the above configuration is provided with splines  111   s  in which the outer peripheries of friction engagement plates (the separator plates) of the brake B 2  are fitted. The first drum portion  111  functions as a brake drum of the brake B 2  that holds the planetary carrier  39  of the second planetary gear mechanism  35  stationary to the transmission case  22  such that the planetary carrier  39  cannot rotate. The inner periphery of the second drum portion  112  is provided with splines in which the outer peripheries of friction engagement plates (the separator plates) of the brake B 1  are fitted. The second drum portion  112  functions as a brake drum of the brake B 1  that holds the second sun gear  36   b  of the second planetary gear mechanism  35  stationary to the transmission case  22  such that the second sun gear  36   b  cannot rotate. 
     As described above, the support member  100  functions as the brake drums of the brakes B 1 , B 2 . This eliminates the need to provide portions functioning as the brake drums in other components of the power transmission device  20  such as the transmission case  22 . In the present embodiment, the boss portion  101 , the wall portion  102 , and the first and second drum portions  111 ,  112  of the support member  100  are formed integrally by casting or forging an aluminum alloy. Therefore, the first and second drum portions  111 ,  112  each also function as a rib. Accordingly, in the power transmission device  20 , an increase in overall size of the device can be restrained, and strength of the support member  100  can be more satisfactorily improved. In the present embodiment, a plurality of ribs  115  are also formed in a radial pattern between the inner peripheral surface of the first drum portion  111  and the wall portion  102 . This can also more satisfactorily improve the strength of the support member  100 . 
     As shown in  FIG. 3 , the brake B 2  that uses the first drum portion  111  of the support member  100  as its brake drum includes a plurality of friction plates  121  that are fitted on the outer peripheral surface of the planetary carrier  39  of the second planetary gear mechanism  35  and that are supported by the planetary carrier  39  such that the friction plates  121  can move, a plurality of separator plates  122  that are fitted in the splines  111   s  formed in the inner peripheral surface of the first drum portion  111  and that are supported by the first drum portion  111  such that the separator plates  122  can move, and a backing plate  123  that is fitted on the spline  111   s  of the first drum portion  111 . 
     Splines that can engage with projections and recesses which are formed in the inner peripheral surface of each friction plate  121  are formed in the outer peripheral surface of the planetary carrier  39  of the second planetary gear mechanism  35 . The friction plate  121  is an annular member having a friction material adhesively attached to both surfaces thereof. The separator plate  122  is an annular member both surfaces of which are smooth. The separator plates  122  are fitted in the splines  111   s  of the first drum portion  111  so as be arranged alternately with the plurality of friction plates  121  fitted on the planetary carrier  39 . The backing plate  123  is fitted in the spline  111   s  of the first drum portion  111  such that the backing plate  123  can contact the friction plate  121  disposed closest to the wall portion  102 . The backing plate  123  is supported in the axial direction by a snap ring attached to the first drum portion  111 . 
     The brake B 2  includes a piston  124  that together with the rear cover  221  defines an engagement oil chamber  130  and that presses the friction plates  121  and the separator plates  122  according to an oil pressure supplied to the engagement oil chamber  130 , and a plurality of return springs  125  that bias the piston  124  in such a direction that the piston  124  is separated from the friction plates  121  and the separator plates  122 . 
     The piston  124  includes an oil chamber defining portion  124   a  that is formed so as to extend substantially along a sidewall portion  221   c  of the rear cover  221 , a pressing portion  124   b  that are extended in the axial direction from the oil chamber defining portion  124   a  and that can press the friction plates  121  and the separator plates  122 , and a spring support portion  124   c  that is extended outward in the radial direction in the shape of a disc from a substantially middle part in the axial direction of the pressing portion  124   b . The piston  124  is disposed inside the rear cover  221  such that the inner periphery of the oil chamber defining portion  124   a  slidingly contacts, via a sealing member, an annular piston support portion  221   d  extended in the axial direction from the sidewall portion  221   c  of the rear cover  221  and such that the outer periphery of the oil chamber defining portion  124   a  slidingly contacts, via a sealing member, a part of the sidewall portion  221   c  which extends in the axial direction. 
     The piston  124  is thus supported by the sidewall portion  221   c  and the piston support portion  221   d  of the rear cover  221  such that the piston  124  can move in the axial direction, and the engagement oil chamber  130  is defined by the oil chamber defining portion  124   a  of the piston  124  and the sidewall portion  221   c  and the piston support portion  221   d  of the rear cover  221 . An engagement oil pressure (hydraulic oil) for engaging the brake B 2  is supplied from the hydraulic control device to the engagement oil chamber  130  via an oil passage, not shown, which is formed in the rear cover  221 . The piston  124  thus moves to press the friction plates  121  and the separator plates  122  according to the engagement oil pressure supplied to the engagement oil chamber  130 , thereby frictionally engaging (fully engaging or slip-engaging) the friction plates  121  and the separator plates  122 . 
     The plurality of return springs  125  are arranged at regular intervals in the circumferential direction of the piston  124  between an tip end  111   b  of the first drum portion  111  and the spring support portion  124   c  extended outward in the radial direction from the pressing portion  124   b  of the piston  124 . As described above, each return spring  125  biases the piston  124  such that the piston  124  is separated from the friction plates  121  and the separator plates  122 . If an oil pressure supplied from the hydraulic control device to the engagement oil chamber  130  decreases, the piston  124  is separated from the friction plates  121  and the separator plates  122  by the biasing force of each return spring  125 , whereby the brake B 1  is disengaged. 
     An oil passage structure that supplies lubricating oil to the brake B 2  having the above configuration will be described below. As shown in  FIG. 3 , a lubricating oil supply path  150  through which lubricating oil from the hydraulic control device, not shown, is supplied to the brake B 2  is formed in the support member  100  including the first drum portion  111  that functions as the brake drum of the brake B 2 . 
     The lubricating oil supply path  150  includes a first oil passage  151  extending in the projecting portion  114  formed in the support member  100 , a second oil passage  152  communicating with the first oil passage  151  and extending in the axial direction in the first drum portion  111 , a third oil passage  153  communicating with the second oil passage  152  and defined by the inner peripheral surface of the wall portion  221   b  of the rear cover  221  and an annular recess  111   o  formed in the outer peripheral surface  110   s  of the first drum portion  111 , and a plurality of through holes  154  communicating with the third oil passage  153  and extending in the radial direction. 
     The first oil passage  151  is connected to a lubricating system of the hydraulic control device, not shown, via an oil passage formed in the transmission case  22  that contacts the projecting portion  114 . The second oil passage  152  is formed in the first drum portion  111  so as to extend from the terminal end of the first oil passage  151  to the stepped part  111   a  that contacts the end face  221   a  of the rear cover  221 . The second oil passage  152  is open at the stepped part  111   a . A sealing member is interposed between the end face  221   a  of the rear cover  221  and the stepped part  111   a  of the first drum portion  111  which contact each other at a position outside the second oil passage  152 . In the present embodiment, the sealing member is disposed in a recess formed in the rear cover  221 . However, a recess where the sealing member is disposed may be formed in the stepped part  111   a  of the first drum portion  111 . 
     The recess  111   o  that defines the third oil passage  153  is formed in an annular shape along the outer peripheral surface  110   s  of the first drum portion  111 , except for the tip end  111   b  of the first drum portion  111 , that is fitted in the wall portion  221   b  of the rear cover  221 . This can restrain an increase in thickness of the rear cover  221  and the first drum portion  111  associated with formation of the third oil passage  153  (the lubricating oil supply path  150 ). A sealing member is interposed between the inner peripheral surface of the wall portion  221   b  of the rear cover  221  and the outer peripheral surface  110   s  of the tip end  111   b  of the first drum portion  111 . In the present embodiment, this sealing member is disposed in a recess formed in the wall portion  221   b  of the rear cover  221 . However, a recess where this sealing member is disposed may be formed in the outer periphery of the tip end  111   b  of the first drum portion  111 . 
     The plurality of through holes  154  are formed in the first drum portion  111  so as to extend from the bottom of the recess  111   o  formed in the outer peripheral surface  110   s  of the first drum portion  111  to the bottoms of the splines  111   s  formed in the inner peripheral surface of the first drum portion  111 . As shown in  FIG. 3 , the plurality of through holes  154  are formed at predetermined intervals in the axial direction along the respective bottoms of the splines  111   s . The plurality of through holes  154  may be formed in all the bottoms of the splines  111   s  or may be formed in some of the bottoms of the splines  111   s.    
     According to such an oil passage structure, lubricating oil can be directly and sufficiently supplied from the lubricating system of the hydraulic control device to the friction plates  121  and the separator plates  122  of the brake B 2  via the lubricating oil supply path  150 , and the friction plates  121  and the separator plates  122  can be more satisfactorily lubricated and cooled. As shown in  FIG. 3 , the friction plates  121  and the separator plates  122  of the brake B 1  are fitted in the splines  111   s  of the first drum portion  111  so that the friction plates  121  and the separator plates  122  except the separator plate  122  disposed closest to the piston  124  are located inside the recess  111   o  (within the range where the recess  111   o  is formed in the first drum portion  111 ). Lubricating oil can thus be uniformly supplied to the friction plates  121  and the separator plates  122  via the recess  111   o , which forms the third oil passage  153  of the lubricating oil supply path  150 , and the plurality of through holes  154 . Lubricating oil that flows from the input shaft  26  side toward the outer periphery through the second planetary gear mechanism  35  is also supplied to the friction plates  121  and the separator plates  122  via an oil hole, not shown, which is formed in the planetary carrier  39 . 
     As described above, in the power transmission device  20  of the present embodiment, lubricating and cooling performance for the brake B 2  which is engaged when a starting speed (first speed) with a high gear ratio is formed (see  FIG. 2 ) and for which relatively large torque capacity is required can be very satisfactorily improved. As a result, slip engagement of the brake B 2  can be effectively used in a wide range. Accordingly, judders (vibration) of the brake B 2  can be more satisfactorily restrained when the starting speed is formed by engaging the brake B 2 , when engine brake is in operation in the vehicle etc., or when the second speed is formed by disengaging the brake B 2 . These operations can thus be smoothly performed. This can also improve a feeling of torque transmission at the time these shift speeds are formed or the engine brake is in operation. 
     In addition, the improved lubricating and cooling performance for the brake B 2  allows slip engagement of the brake B 2  to be used in more situations. A one-way clutch that restricts rotation of the planetary carrier  39  in one direction therefore need not be used to form the starting speed for which relatively large torque capacity is required in order to hold the planetary carrier  39  of the second planetary gear mechanism  35  stationary to the transmission case  22  such that the planetary carrier  39  cannot rotate. That is, the power transmission device  20  can carry out a function similar to that of the one-way clutch by fully engaging and slip-engaging the brake B 2 . The one-way clutch can thus be omitted from the device, and the overall weight of the device can be reduced. 
     In the case of using the one-way clutch that restricts rotation of the planetary carrier  39  of the second planetary gear mechanism  35  in one direction, an outer race of the one-way clutch, in addition to the separator plates  122  of the brake B 2  etc., need to be fitted in the splines  111   s  of the first drum portion  111 . However, omitting the one-way clutch from the power transmission device  20  as in the present embodiment increases the degree of design freedom of the first drum portion  111  and the brake B 2 . For example, the spline  111   s  of the first drum portion  111  can be designed by taking only the relationship with the separator plates  122  of the brake B 2  into consideration. As a result, sufficient space can be secured around the brake B 2 , and the plurality of return springs  125  of the brake B 2  can be disposed without interfering with the splines  111   s  of the first drum portion  111 . As described above, in the present embodiment, the plurality of return springs  125  are arranged at regular intervals in the circumferential direction of the piston  124  between the tip end  111   b  (the end face thereof) of the first drum portion  111  and the spring support portion  124   c . The biasing force of the plurality of return springs can thus be uniformly applied to the piston  124 . This restrains tilting of the piston  124  and allows the piston  124  to press the friction plates  121  and the separator plates  122  such that the friction plates  121  and the separator plates  122  are not tilted. The brake B 2  can thus be slip-engaged more accurately. 
     As described above, the power transmission device  20  includes the brake B 2  that holds the planetary carrier  39  of the second planetary gear mechanism  35  of the automatic transmission  25  stationary to the transmission case  22  such that the planetary carrier  39  cannot rotate, and the support member  100  that rotatably supports the counter drive gear  41  and that is fixed to the transmission case  22 . The support member  100  includes the cylindrical boss portion  101  that rotatably supports the counter drive gear  41 , the wall portion  102  that is extended outward in the radial direction of the automatic transmission  25  from one end of the boss portion  101 , and the cylindrical first drum portion  111  that is extended in the same direction as that of the boss portion  101  and in the axial direction from the wall portion  102  and that functions as the brake drum of the brake B 2 . The support member  100  thus has a function of the brake drum of the brake B 2 , which eliminates the need to provide a portion functioning as the brake drum of the brake B 2  in other components of the power transmission device  20  such as the transmission case  22 . Since the boss portion  101 , the wall portion  102 , and the first drum portion  111  of the support member  100  are formed integrally, the first drum portion  111  also functions as a rib. The strength of the support member  100  can therefore be satisfactorily improved. Accordingly, in this power transmission device  20 , an increase in size of the power transmission device  20  can be restrained, and the strength of the support member  100  that rotatably supports the counter drive gear  41  to which power from the automatic transmission  25  is transmitted can be more satisfactorily improved. 
     This power transmission device  20  may include the brake B 1  that holds the second sun gear  36   b  of the second planetary gear mechanism  35  of the automatic transmission  25  stationary to the transmission case  22  such that the second sun gear  36   b  cannot rotate. The support member  100  includes the cylindrical second drum portion  112  that is extended in the opposite direction to that of the boss portion  101  and the first drum portion  111  and in the axial direction from the wall portion  102  and that functions as the brake drum of the brake B 1 . The second drum portion  112  is formed integrally with the boss portion  101 , the wall portion  102 , and the first drum portion  111 . The support member  100  thus has a function as the brake drum of the brake B 1 , which eliminates the need to provide a portion functioning as the brake drum of the brake B 1  in other components of the power transmission device  20  such as the transmission case  22 . Since the second drum portion  112  is formed integrally with the boss portion  101 , the wall portion  102 , the first drum portion  111 , the second drum portion  112  also functions as a rib. This can restrain an increase in size of the power transmission device  20  and can more satisfactorily improve the strength of the support member  100 . 
     The first drum portion  111  and the second drum portion  112  are extended in the opposite directions to each other from substantially the same position in the radial direction in the outer periphery of the wall portion  102 . 
     The brake B 2  has the plurality of separator plates  122  that are fitted in the splines  111   s  formed in the inner peripheral surface of the first drum portion  111 , and the lubricating oil supply path  150  through which lubricating oil is supplied to the plurality of separator plates  122  and the plurality of friction plates  121  frictionally engaging with the plurality of separator plates  122  is formed in the support member  100 . A sufficient amount of lubricating oil can thus be supplied to the friction plates  121  and the separator plates  122  of the brake B 2  via the lubricating oil supply path  150 , and the friction plates  121  and the separator plates  122  can be more satisfactorily lubricated and cooled. As a result, slip engagement of the brake B 2  can be effectively used in a wide range, whereby the shift speeds can be smoothly formed by engaging or disengaging the brake B 2 , and a feeling of torque transmission can further be improved. 
     Moreover, the transmission case  22  includes the rear cover  221  that accommodates at least the second planetary gear mechanism  35 . The support member  100  is fixed to the rear cover  221  such that the first drum portion  111  is fitted in the rear cover  221 . The lubricating oil supply path  150  includes the third oil passage  153  defined by the inner peripheral surface of the wall portion  221   b  of the rear cover  221  and the recess  111   o  formed in the outer peripheral surface of the first drum portion  111 , and the plurality of through holes  154  communicating with the third oil passage  153  and extending in the radial direction. At least a part of the friction plates  121  and the separator plates  122  is fitted in the first drum portion  111  so as to be located inside the recess  111   o . Since the support member  100  is fixed to the rear cover  221  such that the first drum portion  111  is fitted in the rear cover  221 , the support member  100  can be more firmly fixed to the transmission case  22 . Since the third oil passage  153  forming the lubricating oil supply path  150  is defined by the inner peripheral surface of the rear cover  221  and the recess  111   o  formed in the outer peripheral surface of the first drum portion  111 , this can restrain an increase in thickness of the rear cover  221  and the first drum portion  111  associated with formation of the lubricating oil supply path  150 . Moreover, since at least a part of the friction plates  121  and the separator plates  122  is fitted in the first drum portion  111  so as to be located inside the recess  111   o , lubricating oil can be uniformly supplied to the friction plates  121  and the separator plates  122  via the recess  111   o  and the plurality of through holes  154 . 
     The brake B 2  includes the piston  124  that together the transmission case  22  defines the engagement oil chamber  130  and that presses the friction plates  121  and the separator plates  122  according to an oil pressure supplied to the engagement oil chamber  130 , and the plurality of return springs  125  that bias the piston  124  such that the piston  124  is separated from the friction plates  121  and the separator plates  122 . The plurality of return springs  125  are disposed between the tip end  111   b  of the first drum portion  111  and the piston  124 . The plurality of return springs  125  can thus be disposed without interfering with the splines  111   s  of the first drum portion  111  in which the separator plates  122  are fitted. Accordingly, the plurality of return springs  125  can be arranged at regular intervals in the circumferential direction of the piston  124 , and the biasing force of the plurality of return springs  125  can be uniformly applied to the piston  124 . This restrains tilting of the piston  124  and allows the piston  124  to press the friction plates  121  and the separator plates  122  such that the friction plates  121  and the separator plates  122  are not tilted. The brake B 2  can thus be slip-engaged more accurately. 
     Moreover, the brake B 2  is engaged when the automatic transmission  25  forms the starting speed. Accordingly, slip engagement of the brake B 2  is effectively used when the starting speed is formed. The starting speed can thus be smoothly formed, and a feeling of torque transmission can further be improved. 
     However, the brake B 2  may be any brake that can hold one of rotary elements included in the automatic transmission  25  stationary to the transmission case  22  such that the rotary element cannot rotate. The brake B 2  is not limited to the brake that is engaged when the starting speed is formed. The brake B 1  may be any brake that can hold a second rotary element, which is different from the rotary element that is held stationary by the brake B 2  such that the rotary element cannot rotate, stationary to the transmission case  22  such that the second rotary element cannot rotate. Moreover, the second drum portion  112  that functions as the brake drum of the brake B 1  may be omitted from the support member  100 . In this case, other components included in the power transmission device  20  can be used as the brake drum of the brake B 1 . 
     The first drum portion  111  of the support member  100  need not necessarily be fitted in the wall portion  221   b  of the rear cover  221 . Moreover, the lubricating oil supply path  150  formed in the support member  100  is not limited to the configuration of the present embodiment. For example, the third oil passage  153  of the lubricating oil supply path  150  may be defined by the outer peripheral surface  110   s  of the first drum portion  111  that is fitted in the wall portion  221   b  of the rear cover  221  and a recess that is formed in the wall portion  221   b  of the rear cover  221  so as to extend along the outer peripheral surface  110   s . The lubricating oil supply path  150  may be omitted from the support member  100 , and only the lubricating oil that flows from the input shaft  26  side toward the outer periphery through the second planetary gear mechanism  35  may be supplied to the friction plates  121  and the separator plates  122  of the brake B 2  via the oil hole, not shown, which is formed in the planetary carrier  39 . 
     The plurality of return springs  125  of the brake B 1  are not limited to the return springs disposed between the tip end  111   b  of the first drum portion  111  and the piston  124 . The plurality of return springs  125  may be any return springs that are disposed between a member fixed to the transmission case  22  and the piston  124 . For example, the wall portion  221   b  of the rear cover  221  may have an extended portion extended inward in the radial direction from the wall portion  221   b , and the plurality of return springs  125  may be disposed between the extended portion and the piston  124 . Although the automatic transmission  25  included in the power transmission device  20  of the present embodiment does not have a one-way clutch that restricts rotation of the planetary carrier  39  of the second planetary gear mechanism  35  in one direction, the present disclosure may be applied to a power transmission device including an automatic transmission having such a one-way clutch. 
     Correspondence between the main elements of the above embodiment etc. and the main elements of the disclosure described in “SUMMARY” will be described. In the above embodiment etc., the power transmission device  20  including the automatic transmission  25 , the transmission case  22  accommodating the automatic transmission  25 , and the counter drive gear  41  to which power from the automatic transmission  25  is transmitted corresponds to the “power transmission device.” The brake B 2  that holds the planetary carrier  39  of the second planetary gear mechanism  35  of the automatic transmission  25  stationary to the transmission case  22  such that the planetary carrier  39  cannot rotate corresponds to the “brake.” The cylindrical boss portion  101  that rotatably supports the counter drive gear  41  corresponds to the “boss portion.” The wall portion  102  extended outward in the radial direction of the automatic transmission  25  from one end of the boss portion  101  corresponds to the “wall portion.” The cylindrical first drum portion  111  extended in the same direction as that of the boss portion  101  and in the axial direction from the wall portion  102  and functioning as the brake drum of the brake B 2  corresponds to the “drum portion.” The support member  100  including the boss portion  101 , the wall portion  102 , and the first drum portion  111  and fixed to the transmission case  22  corresponds to the “support member.” The brake B 1  that holds the second sun gear  36   b  of the second planetary gear mechanism  35  of the automatic transmission  25  stationary to the transmission case  22  such that the second sun gear  36   b  cannot rotate corresponds to the “second brake.” The cylindrical second drum portion  112  extended in the opposite direction to that of the boss portion  101  and the first drum portion  111  and in the axial direction from the wall portion  102  of the support member  100  and functioning as the brake drum of the brake B 2  corresponds to the “second drum portion.” The plurality of separator plates  122  of the brake B 2  corresponds to the “plurality of friction engagement plates.” The lubricating oil supply path  150  formed in the support member corresponds to the “lubricating oil supply path.” The rear cover  221  accommodating at least the second planetary gear mechanism  35  corresponds to the “case portion.” The third oil passage  153  defined by the inner peripheral surface of the rear cover  221  and the recess  111   o  formed in the outer peripheral surface  110   s  of the first drum portion  111  corresponds to the “oil passage.” The plurality of through holes  154  communicating with the third oil passage and extending in the radial direction correspond to the “plurality of through holes.” The piston  124  that together with the transmission case  22  defines the engagement oil chamber  130  and that presses the friction plates  121  and the separator plates  122  according to an oil pressure supplied to the engagement oil chamber  130  corresponds to the “piston.” The plurality of return springs  125  that bias the piston  124  such that the piston  124  is separated from the friction plates  121  and the separator plates  122  correspond to the “plurality of return springs.” 
     Although the embodiment of the present disclosure is described above, it should be understood that the present disclosure is not limited in any way to the above embodiment, and various modifications can be made without departing from the spirit and scope of the present disclosure. The above mode for carrying out the disclosure is merely shown as a specific form of the disclosure described in “SUMMARY” and is not intended to limit the elements of the disclosure described in “SUMMARY.” 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to manufacturing industries of power transmission devices, etc.