Abstract:
An automatic transmission for a motorcycle includes a fluid torque converter and a geartrain. The torque converter includes a torque converter housing, a torque converter input pulley arranged to receive rotary power from the motorcycle engine and a torque converter output shaft for transmitting rotary power. The geartrain includes a main shaft driven by the torque converter output and a parallel countershaft. The main shaft carries a plurality of main gears. The countershaft carries a plurality of counter gears forming selectable gear pairs with the main gears. An output pulley driven by the countershaft is rotatably carried on the main shaft between the torque converter and the gear pairs. The output pulley and the torque converter input pulley are on a same side of the transmission.

Description:
FIELD OF THE INVENTION 
   This invention relates in general to transmissions and in particular to motorcycle transmissions. 
   BACKGROUND OF THE INVENTION 
   HARLEY DAVIDSON motorcycle owners are loyal and enthusiastic about their motorcycles. Owners of HARLEY DAVIDSON motorcycles are generally not reluctant to modify, customize or improve their motorcycles. Aftermarket parts and kits to modify HARLEY DAVIDSON motorcycles are popular. 
   The traditional HARLEY DAVIDSON drivetrain includes a V-TWIN engine positioned forward the transmission in which both the engine and transmission are independently secured or bolted together and secured to the motorcycle frame. In particular, HARLEY DAVIDSON V-TWIN engine motorcycles incorporate separate cases for the engine and the transmission. 
   In one well-known configuration, the drivetrain assembly comprises a leftside drive in which the engine includes a crankshaft and output shaft substantially parallel to an input shaft of the transmission. Engine power is coupled to the transmission with a primary belt or chain interconnecting the parallel output and inputs shafts of the engine and transmission respectively. The drive assembly additionally includes a primary drive housing on the leftside of the motorcycle for enclosing the primary belt or chain interconnecting the parallel output and input shafts. 
   The present inventors have recognized that as riders of motorcycles age, the strength and coordination required to clutch and shift a four or five-speed motorcycle transmission using coordinated movement of arms and legs, can be problematic. The coordinated movements can become too physically taxing for older riders. 
   The present inventors have recognized the desirability of providing motorcycles, particularly HARLEY DAVIDSON and like motorcycles with a compact and effective automatic transmission that can make the motorcycle more easily operated by older riders or physically impaired riders. 
   The present inventors have recognized that the HARLEY DAVIDSON V-TWIN engine motorcycle is a likely candidate for a transmission modification to accommodate an automatic transmission given the separate casings for the engine and transmission on these motorcycles. 
   There have been attempts to provide a motorcycle with an automatic transmission. Such attempts include those disclosed in U.S. Pat. Nos. 6,390,262; 4,702,340; 5,951,434; 6910,987 and 5,862,717. Some of the embodiments described in these patents however suffer the drawbacks of providing an automatic transmission that is overly complex, bulky, or not adaptable to be easily installed on a HARLEY DAVIDSON motorcycle. 
   SUMMARY OF THE INVENTION 
   The invention provides an automatic transmission for a motorcycle including a torque converter and a geartrain. The torque converter includes a torque converter housing, a torque converter input pulley arranged to receive rotary power from the motorcycle engine and a torque converter output shaft for transmitting rotary power. The torque converter includes fluid coupling elements arranged within the housing to transmit torque between the torque converter input pulley and the torque converter output shaft. 
   The geartrain includes a main shaft for receiving rotary power from the torque converter output and a countershaft arranged in parallel to the main shaft. The main shaft carries a plurality of main gears. The countershaft carries a plurality of counter gears. A plurality of gear pairs are formed by each of the main gears being arranged to form one gear pair with one of the counter gears, the gear pairs being in constant mesh. An output pulley is rotatably mounted on the main shaft between the torque converter and the plurality of gear pairs. A plurality of clutch devices are arranged to select a gear pair from the plurality of gear pairs that will transmit torque to the output pulley. 
   According to one preferred embodiment, at least one clutch device comprises a clutch plate or drum fixed on the main shaft, and at least one clutch friction disk arranged between the clutch plate and one gear of the select gear pair. The friction disk is selectively engageable to the clutch plate and to the one gear to transmit torque between the clutch plate and the one gear. 
   According to another preferred embodiment, at least one clutch device comprises a clutch plate fixed on the countershaft, and at least one clutch friction disk arranged between the clutch plate and one gear of the select gear pair. The friction disk is selectively engageable to the clutch plate and to the one gear to transmit torque between the clutch plate and the one gear. 
   The geartrain can be a four speed geartrain, wherein a first gear is furthest from the torque converter. A second gear can be located between the first gear and the torque converter. A third gear can be located between the second gear and the torque converter. A fourth gear can be located between the third gear and the output pulley. 
   According to the preferred embodiment, the torque converter input pulley is located between the torque converter and the output pulley and the torque converter input pulley and the output pulley are coaxially arranged. 
   According to a preferred embodiment the clutch devices each comprise one clutch plate fixed to the main shaft or the counter shaft and has engageable opposite sides. The clutch plate is arranged between alternately selectable gear pairs, and at least one friction disk is arranged between each of the selectable gear pairs and one engageable opposite side of the clutch plate. Each friction disk is selectively actuatable to engage one gear of the selectable gear pair to the clutch plate to transmit torque between the clutch plate and the selectable gear pair to transmit torque to the output pulley. 
   The transmission assembly of the present invention provides a compact, relatively simple automatic transmission that is particularly adapted for use on HARLEY DAVIDSON motorcycles, and other motorcycles that incorporate a separate casing for each of the engine and transmission. The transmission assembly of the present invention can also be incorporated into motorcycles that use a common casing for the engine and the transmission, with some additional modifications. Furthermore the invention may be useful for other type vehicles where a compact design is advantageous. 
   Numerous other advantages and features of the present invention will be become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic side view of a motorcycle that incorporates the present invention; 
       FIG. 2  is a schematic plan view of a drivetrain of the motorcycle of  FIG. 1 ; 
       FIG. 3  is a schematic plan view of the transmission shown in  FIG. 2 ; 
       FIG. 4  is a schematic plan view of the transmission of  FIG. 3  with the transmission shown in first gear configuration; 
       FIG. 5  is a schematic plan view of the transmission of  FIG. 3  with the transmission shown in second gear configuration; 
       FIG. 6  is a schematic plan view of the transmission of  FIG. 3  with the transmission in third gear configuration; 
       FIG. 7  is a schematic plan view of the transmission of  FIG. 3  with the transmission shown in fourth gear configuration; and 
       FIG. 8  is a schematic plan view of an alternate embodiment transmission with the transmission shown in first gear configuration; 
       FIG. 9  is a schematic plan view of the transmission of  FIG. 8  with the transmission shown in second gear configuration; 
       FIG. 10  is a schematic plan view of the transmission of  FIG. 8  with the transmission in third gear configuration; 
       FIG. 11  is a schematic plan view of the transmission of  FIG. 8  with the transmission shown in fourth gear configuration; 
       FIG. 12  is a schematic control diagram of the invention, with a countershaft assembly removed for clarity of depiction; and 
       FIG. 13  is an enlarged, fragmentary, schematic, sectional view of a clutch arrangement used in the preferred embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
     FIG. 1  illustrates a motorcycle  10  including a frame  14 . A seat  18 , a fuel tank  22 , front and rear wheels  26 ,  30 , engine  34  and a transmission assembly  38  are mounted to the frame  14 . The engine  34  illustrated is a V-TWIN engine popular on HARLEY DAVIDSON motorcycles. 
     FIG. 2  illustrates a drive train  39  of the motorcycle shown in  FIG. 1 . The drive train  39  includes the engine  34 , the transmission assembly  38  and the rear wheel  30 . The engine  34  transmits rotary power via its crankshaft to an engine output shaft  46 . The engine output shaft  46  is connected to an engine drive sprocket  48 . 
   The transmission assembly  38  includes a torque converter  52  that has a torque converter drive sprocket  54 . 
   A primary drive chain  56  is wrapped around the engine drive sprocket  48  and the torque converter drive sprocket  54 . An oil pump  58  that provides transmission oil or fluid to the torque converter is also driven to rotate, and pump oil, by the circulating drive chain  56 . Alternately, the oil pump can be driven directly by a gearing relationship (not shown) to the torque converter  52  or the drive sprocket  54 . The transmission assembly  38  includes a transmission output pulley  62 . A rear drive pulley  66  is operatively connected to the rear wheel  30  to rotate the rear wheel  30 . A secondary drive chain  68  is wrapped around the output pulley  62  and the rear drive pulley  66 . 
   The terms “sprocket” and “pulley” denote elements having outside features that are engageable by either a chain or a belt, to be rotated. A sprocket and a pulley can be identical in structure, and accordingly the terms are used interchangeably herein. 
   First Embodiment of the Invention 
     FIG. 3  illustrates the transmission assembly  38 . The torque converter  52  includes a torque converter housing  72 . Within the housing  72  are a driving rotary element  74  and a driven rotary element  76 . The torque converter is shown in a simplistic way. For example, a stator can also be included within the housing between the driving rotary element  74  and the driven rotary element  76 . Torque converters are well known and are described for example in U.S. Pat. Nos. 4,070,925; 5,862,717; 2,897,690; 2,449,608; 6,655,226; 6,390,262; and 6,805,026, all herein incorporated by reference. According to one possible embodiment, a relatively small torque converter such as one available from a HONDA automobile could be made to work in a satisfactory manner. The torque converter housing  72 , the driving rotary element  74 , and the input pulley  54  are all fixed to rotate together. The driven rotary element  76  is fixed to a main shaft  86  of the transmission assembly  38 . The torque converter housing  72  is journaled on the main shaft  86  or on a suitable extension thereof, by bearings and oil seals (not shown). 
   The main shaft  86  penetrates into a transmission casing  87  (shown in  FIG. 2 ) of the transmission assembly  38 . The main shaft  86  receives rotary power from the torque converter  52  via a fluid coupling between the driving rotary element  74  and the driven rotary element  76 , by rotation of the torque converter components  54 ,  72 ,  74 . The main shaft  86  transmits rotary power to clutch plates  92 ,  96  that are fixed on the main shaft  86  to rotate therewith. The clutch plates  92 ,  96  can be keyed or splined to the shaft  86  or otherwise fixedly fastened to the shaft  86 . The clutch plates include clutch engaging opposite sides  92   a ,  92   b ;  96   a ,  96   b.    
   Preferably, the clutch assemblies are multiple disk wet clutches. The clutch plates are shown schematically as flat plates but are preferably of a drum configuration having a plurality of friction plates that are interleaved with friction disks of the clutch friction disk assembly such as shown and described in  FIG. 13  and U.S. Pat. Nos. 4,623,055; 5,103,953; 4,131,185 or 3,266,608, all incorporated by reference. 
   The output pulley  62 , a first drive gear  102 , a second drive gear  104 , a third drive gear  106 , and a fourth drive gear  108  are mounted axially on the main shaft  86  but are free to rotate on the main shaft, i.e., are relatively rotatable with respect to the main shaft  86 . The fourth drive gear  108  is fixed to the output pulley  62 . 
   Clutch friction disks  116  are mounted on the main shaft  86  between the fourth drive gear  108  and the clutch plate  92 . Clutch friction disks  118  are mounted on the main shaft  86  between the clutch plate  92  and the third drive gear  106 . The clutch friction disks  116 ,  118  are free to rotate on the main shaft  86 , i.e., are relatively rotatable with respect to the main shaft  86 . The clutch disks  116  can be fastened to the fourth drive gear  108  to rotate therewith. The clutch disks  118  can be fastened to the third drive gear  106  to rotate therewith. 
   Clutch friction disks  126  are mounted on the main shaft  86  between the second drive gear  104  and the clutch plate  96 . Clutch friction disks  128  are mounted on the main shaft  86  between the clutch plate  96  and the first drive gear  102 . The clutch friction disks  126 ,  128  are free to rotate on the main shaft  86 , i.e., are relatively rotatable with respect to the main shaft  86 . The clutch friction disks  126  can be fastened to the second drive gear  104  to rotate therewith. The clutch disks  128  can be fastened to the first drive gear  102  to rotate therewith. 
   A countershaft  132  is mounted within the transmission casing  87 , parallel to the main shaft  86 . A first counter gear  136 , a second counter gear  138 , a third counter gear  140 , and a fourth counter gear  142  are all fixedly mounted on the countershaft  132  to rotate therewith, i.e., there is no relative rotation between the gears  136 ,  138 ,  140 ,  142  and the countershaft  132 . The gears  136 ,  138 ,  140 ,  142  can be keyed or splined to the countershaft  132  or otherwise fixedly fastened to the countershaft  132 . 
   The gears  102 ,  104 ,  106 ,  108 ,  136 ,  138 ,  140 ,  142  all have outer circumferential teeth. The gear pairs  102 ,  136 ;  104 ,  138 ;  106 ,  140  and  108 ,  142  are each in constant meshing relationship. 
     FIG. 3  illustrates a symbol key for “clutch disengaged” and “clutch engaged” which is correct for  FIGS. 4 through 11 .  FIG. 3  illustrates the transmission assembly  38  in a neutral gear mode since none of the clutches is engaged. 
     FIG. 4  illustrates the operation of the transmission in first gear mode. The torque converter  52  is turned via the input pulley  54 . A fluid coupling within the torque converter turns the main shaft  86 . The main shaft  86  turns the clutch plate  96  which turns first gear  102  via the clutch friction disks  128  which are selected by a controller  145  ( FIG. 12 ) to be engaged to the clutch plate  96 . First gear  102  turns the corresponding first counter gear  136 , which turns the countershaft  132 , which turns the fourth counter gear  142 , which turns the fourth gear  108  that is fixed to the output pulley  62 . The output pulley  62  is turned, which turns the rear wheel  30  via the drive sprocket  66  and the secondary chain  68 . 
     FIG. 5  illustrates the operation of the transmission in second gear mode. The torque converter  52  is turned via the input pulley  54 . A fluid coupling within the torque converter turns the main shaft  86 . The main shaft  86  turns the clutch plate  96 , which turns the second gear  104  via the clutch friction disks  126  which are selected by the controller  145  to be engaged to the clutch plate  96 . Second gear turns the corresponding second counter gear  138 , which turns the countershaft  132 , which turns the fourth counter gear  142 , which turns the fourth gear  108  which is fixed to the output pulley  62 . The output pulley  62  is turned which turns the rear wheel  30  via the drive sprocket  66  and the secondary chain  68 . 
     FIG. 6  illustrates the operation of the transmission in third gear mode. The torque converter  52  is turned via the input pulley  54 . A fluid coupling within the torque converter turns the main shaft  86 . The main shaft  86  turns the clutch plate  92  which turns third gear  106  via the clutch friction disks  118  which are selected by the controller  145  to be engaged to the clutch plate  92 . Third gear  106  turns the corresponding third counter gear  140  which turns the countershaft  132 , which turns the fourth counter gear  142  which turns the fourth gear  108  which is fixed to the output pulley  62 . The output pulley  62  is turned which turns the rear wheel  30  via the drive sprocket  66  and the secondary chain  68 . 
     FIG. 7  illustrates the operation of the transmission in fourth gear mode. The torque converter  52  is turned via the input pulley  54 . A fluid coupling within the torque converter turns the main shaft  86 . The main shaft  86  turns the clutch plate  92  which turns fourth gear  108  via the clutch friction disks  116  which are selected by the controller  145  to be engaged to the clutch plate  92 . Fourth gear  108  turns the output pulley which is fixed thereto. The output pulley  62  is turned which turns the rear wheel  30  via the drive sprocket  66  and the secondary chain  68 . 
   Second Embodiment of the Invention 
     FIG. 8  illustrates an alternate transmission assembly  160 . Unless otherwise stated the components for the second embodiment are the same as for the first embodiment. The torque converter  52  is the same as described in the first embodiment. The driven rotary element  76  is fixed to a main shaft  186  of the transmission assembly  160 . The torque converter housing  72  is journaled on the main shaft  186  or on a suitable extension thereof, by bearings and oil seals (not shown). 
   The main shaft  186  penetrates into the transmission casing  87  (shown in  FIG. 2 ) of the transmission assembly  160 . The main shaft  186  receives rotary power from the torque converter  52  via a fluid coupling between the driving rotary element  74  and the driven rotary element  76 , by rotation of the torque converter components  54 ,  72 ,  74 . The main shaft  186  transmits rotary power to a clutch plate  192  that is fixed on the main shaft  186  to rotate therewith. The clutch plate  192  can be keyed or splined to the shaft  186  or otherwise fixedly fastened to the shaft  186 . The clutch plate  192  includes clutch engaging opposite sides  192   a ,  192   b  ( FIG. 9 ). 
   The output pulley  62 , a first drive gear  202 , a second drive gear  204 , a third drive gear  206  and a fourth drive gear  208  are axially mounted on the main shaft  186 . The third drive gear  206  and the fourth drive gear  208  are free to rotate on the main shaft, i.e., are relatively rotatable with respect to the main shaft  86 . The fourth drive gear  108  is fixed to the output pulley  62 . The first drive gear  202  and the second drive gear  204  are fixed to the main shaft  186  to rotate therewith. The first drive gear  202  when the second drive gear  204  can be keyed or splined to the shaft  186  or otherwise fixedly fastened to the shaft  186 . 
   Clutch friction disks  216  are mounted on the main shaft  186  between the fourth drive gear  208  and the clutch plate  192 . Clutch friction disks  218  are mounted on the main shaft  186  between the clutch plate  192  and the third drive gear  206 . The clutch friction disks  216 ,  218  are free to rotate on the main shaft  186 , i.e., are relatively rotatable with respect to the main shaft  186 . The clutch friction disks  216  can be fastened to the fourth drive gear  208  to rotate therewith. The clutch friction disks  218  can be fastened to the third drive gear  206  to rotate therewith. 
   A countershaft  232  is mounted within the transmission casing  87 , parallel to the main shaft  186 . The countershaft transmits rotary power to a clutch plate  196  that is fixed on the countershaft  232  to rotate therewith. The clutch plate  196  can be keyed or splined to the countershaft  232  or otherwise fixedly fastened to the countershaft  232 . The clutch plate  196  includes clutch engaging opposite sides  196   a ,  196   b  ( FIG. 11 ). 
   A first counter gear  236 , a second counter gear  238 , a third counter gear  240  and a fourth counter gear  242  are axially mounted on the countershaft  232 . The third counter gear  240  and the fourth counter gear  242  are fixed to the countershaft  232  to rotate therewith, i.e., there is no relative rotation between the gears  240 ,  242  and the countershaft  232 . The counter gears  240 ,  242  can be keyed or splined to the countershaft  232  or otherwise fixedly fastened to the shaft  232 . The first counter gear  236  and the second counter gear  238  are rotatably mounted on the countershaft  232 , i.e., are free to rotate on the countershaft  232 . 
   Clutch friction disks  226  are mounted on the countershaft  232  between the second counter gear  238  and the clutch plate  196 . Clutch friction disks  228  are mounted on the countershaft  232  between the clutch plate  196  and the first counter gear  236 . The clutch friction disks  226 ,  228  are free to rotate on the countershaft  232 , i.e., are relatively rotatable with respect to the countershaft  232 . The clutch friction disks  226  can be fastened to the second counter gear  238  to rotate therewith. The clutch friction disks  228  can be fastened to the first counter gear  236  to rotate therewith. 
   The gears  202 ,  204 ,  206 ,  208 ,  236 ,  238 ,  240 ,  242  all have outer circumferential teeth. The gear pairs  202 ,  236 ;  204 ,  238 ;  206 ,  240  and  208 ,  242  are each in constant meshing relationship. 
     FIG. 8  illustrates the operation of the transmission in first gear mode. The torque converter  52  is turned via the input pulley  54 . A fluid coupling within the torque converter turns the main shaft  186 . The main shaft  186  turns the first gear  202 . First gear  202  turns the corresponding first counter gear  236 . The clutch friction disks  228  are selected by the controller  145  to be engaged to fix the first counter gear  236  for rotation with the clutch plate  196 , which turns the countershaft  232 , which turns the fourth counter gear  242 , which turns the fourth gear  208  which is fixed to the output pulley  62 . The output pulley  62  is turned, which turns the rear wheel  30  via the drive sprocket  66  and the secondary chain  68 . 
     FIG. 9  illustrates the operation of the transmission in second gear mode. The torque converter  52  is turned via the input pulley  54 . A fluid coupling within the torque converter turns the main shaft  186 . The main shaft  186  turns the second gear  204 . Second gear  204  turns the corresponding second counter gear  238 . The clutch friction disks  226  are selected by the controller  145  to be engaged to fix the second counter gear  238  for rotation with the clutch plate  196  which turns the countershaft  232 , which turns the fourth counter gear  242 , which turns the fourth gear  208  which is fixed to the output pulley  62 . The output pulley  62  is turned, which turns the rear wheel  30  via the drive sprocket  66  and the secondary chain  68 . 
     FIG. 10  illustrates the operation of the transmission in third gear mode. The torque converter  52  is turned via the input pulley  54 . A fluid coupling within the torque converter turns the main shaft  186 . The main shaft  186  turns the clutch plate  192  which turns third gear  206  via the clutch friction disks  218  which are selected by the controller  145  to be engaged to the clutch plate  192 . Third gear  206  turns the corresponding third counter gear  240 , which turns the countershaft  232 , which turns the fourth counter gear  242 , which turns the fourth gear  208  which is fixed to the output pulley  62 . The output pulley  62  is turned, which turns the rear wheel  30  via the drive sprocket  66  and the secondary chain  68 . 
     FIG. 11  illustrates the operation of the transmission in fourth gear mode. The torque converter  52  is turned via the input pulley  54 . A fluid coupling within the torque converter turns the main shaft  186 . The main shaft  186  turns the clutch plate  192  which turns fourth gear  208  via the clutch friction disks  216  which are selected by the controller  145  to be engaged to the clutch plate  192 . Fourth gear  208  turns the output pulley which is fixed thereto. The output pulley  62  is turned, which turns the rear wheel  30  via the drive sprocket  66  and the secondary chain  68 . 
   For the embodiment of  FIGS. 8-11 , when none of the clutches is engaged, the controller  145  has selected, or the operator has manually selected, a neutral gear mode. 
     FIG. 12  illustrates a control system  300  of the invention applied to the first embodiment. For purposes of depiction simplicity, the countershaft  132  and the counter gears are not shown. The controller  145  is in signal-communication with clutch engagement devices  304 ,  306 ,  308 ,  310 , through signal conductors  304   a ,  306   a ,  308   a ,  310   a , respectively. The controller  145  receives input signals via sensors  320 . The input signals can be parameters such as engine RPM, transmission RPM, throttle position, engine torque, gear lever position for gear selection, or other parameters. A manual control override  326  can be used to manually select the gear mode of operation. 
   The clutch engagement devices  304 ,  306 ,  308 ,  310  can be electromechanical devices, hydraulic or fluid operate devices such as disclosed in U.S. Pat. Nos. 2,825,235; or 4,627,312, herein incorporated by reference. Preferably, the clutch engagement devices are analog or digital solenoids that control hydraulic actuators. Solenoids can also control torque converter fluid fill and fluid line pressure. The controller correlates the input from the sensors  320  to select the appropriate gear mode of operation, such as a first gear mode, second gear mode, third gear mode or fourth gear mode. The corresponding engagement device  304 ,  306   308 ,  310  is energized to engage the selected one of the friction disks  128 ,  126 ,  118  or  116 , while the respective other friction disks remain disengaged; or no engagement device is engaged so the transmission remains in neutral mode. 
   The controller  145  can be an electronic controller and the system can be an electronic system, such as disclosed in U.S. Pat. Nos. 6,604,438 or 4,627,312, herein incorporated by reference. Alternatively, the controller  145  could be a fluid or pneumatically operated valve selector. Preferably, the controller  145  is a programmable electronic controller (PLC) that sends a signal to one or more electromagnetic valves, or solenoid valves, to control actuation of the clutches. Depending on the type of system and controller  145  and the type of engagement devices  304 ,  306 ,  308 ,  310 , the conductors  304   a ,  306   a ,  308   a ,  310   a  can be electric wires, optical fibers, fluid lines, or other known signal carrying conduit. 
   Although the system  300  is illustrated in  FIG. 12  with respect to the first embodiment, a similar system could be used to control gear shifting in the second embodiment as well, with the friction disks  216 ,  218 ,  226 ,  228  engageable by the engagement devices  310 ,  308 ,  306 ,  304 , respectively, under control of the controller  145  in the same fashion as that described with regard to  FIG. 12 . 
     FIG. 13  is a vertical fragmentary sectional view of a hydraulic clutch arrangement useful in the transmission of the preferred embodiments of the invention. Only the top portion of the sectional view is shown, the bottom portion being mirror image identical. The clutch plate  92  and the clutch friction disks  116 ,  118  and gears  108 ,  106  are shown as an example. The other clutch plates  96 ,  192 ,  196  and associated clutch friction disks and gears can be similarly configured. 
   The clutch plate  92  comprises a drum  408  that forms right and left cylinders  410 ,  412 . Only the left side of  FIG. 13  will be described as the right side is substantially mirror image identical and the operation is identical. The drum  408  can be keyed, splined or otherwise fixed to the shaft  86  at  409 . 
   An annular hydraulic piston  413  fits slidably in the cylinder  412  to form an annular hydraulic chamber  414  between it and the cylinder  412 . The hydraulic chamber  414  is connected through an oil passage  415  in the output shaft  86  and an appropriate hydraulic circuit (not shown) to the hydraulic pump  58 . The gear  108  surrounds the output shaft  86  so as to be relatively rotatable thereon. A bearing (not shown) can be fit between the output shaft  86  and the gear  108 . 
   A boss  419  is integrally provided on the gear  108 , and an external spline  421  and an opposite internal spline  422  are formed on a boss outer periphery and a cylinder inner periphery, respectively. Plural input side annular friction plates  116   a  are slideably fitted onto the external spline  421  at inner peripheral projections  424  of the plates  116   a  and annular facings  420  are securely fixed to both front and rear faces of the friction plates  116   a . Output side annular friction plates  425  are disposed between the adjacent input side annular friction plates  116   a  respectively, and the friction plates  425  are slideably fitted into the internal spline  422  at outer peripheral projection  426  of the plates  425 . The right-most friction plate  116   a  is opposite to a thick annular pressure plate  427 , and the left-most friction plate  116   a  is opposite to a thick annular back plate  428 . 
   The pressure plate  427  and the back plate  428  only slideably fit into the internal spline  422  at the outer peripheral projections  429  and  430  of the pressure plate  427  and back plate  428  respectively, and the back plate  428  contacts with a snap ring  432  (stopper member). In the illustration hydraulic clutch, a friction member  431  comprises the pressure plate  427 , the friction plates  116   a  and  425 , and the back plate  428  respectively. 
   A snap ring  433  (stopper member) is provided on an outer periphery of the output shaft  86 . The snap ring  433  is positioned at a just inner side of the pressure plate  427 . A rear outer peripheral portion of the piston  413  serves as an annular presser face  435 , and only a part serving as an annular projection  434  extends rearward from a rear inner peripheral portion of the piston. 
   Reference numeral  436  designates a coned disc spring. When the clutch is engaged from the clutch disengaged state hydraulic pressure is supplied from the pump  58  through the oil passage  415  etc. to the hydraulic chamber  414 , thus the piston  413  is moved leftward. The load of the piston  413  is transmitted from the projection  434  to the contact portion  438  of the coned disc spring  436  in an early stage of clutch engagement. The piston-contacting portion  438  moves gradually radially outwardly with the increasing contact pressure by the piston. The outer peripheral end  440  of the coned disc spring contacts with the pressure plate  427  of the friction member  431 . Thereafter, the load of the piston  413  begins to be transmitted through the coned disc spring  436  to the friction member  431 . The load of the piston  413  is transmitted to the friction member  431  through the outer peripheral portion of the coned spring  436 . 
   In order to disengage the clutch, it is enough to relieve the hydraulic pressure in the hydraulic chamber  414 , and procedures reverse to the above-mentioned description are carried out in that case. The coned disc spring  436  serves as a return spring in this instance. 
   As an alternative, the disc spring can be eliminated and the piston  413  can press directly on the friction member  431 . 
     FIGS. 1-13  are diagrammatic or schematic drawings and the description herein leaves out information that would be within the knowledge and skill of one of skill in the art. For example, the gears and shafts within the transmission casing would require the necessary bearings and oil seals for proper design and operation. The placement and design of such elements are within the skill of one of ordinary skill in the art. 
   From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred.