referring to fig1 and 2 , a transmission according to the present invention includes an input 10 for driveably connecting a power source , such as an internal combustion engine or electric motor , to the transmission , and an output 12 for driving a load , such as the driven wheels of a motor vehicle , through a powertrain that may include a drive shaft , differential mechanism , and axle shafts . a first friction clutch 14 , consisting of a clutch housing and a clutch disc , alternately connects and disconnects a first input shaft 16 as clutch 14 is engaged and disengaged , respectively . a second friction clutch 18 , consisting of a clutch housing and a clutch disc , connects and disconnects a second input shaft 20 as clutch 18 is engaged and disengaged , respectively . a first output shaft 22 supports a first output pinion 24 , which is secured to shaft 22 in continuous meshing engagement with an output gear 25 , secured to output 12 . a second output shaft 26 supports a second output pinion 28 , which is secured to the shaft in continuous meshing engagement with output gear 25 . an idler shaft 30 and layshaft 32 are arranged substantially parallel to the other shafts 16 , 20 22 and 26 . first pairs of mutually engaged pinions and gears include a pinion 34 , secured to input shaft 16 and engaged with gear 36 , which is supported on shaft 22 for rotation relative to shaft 22 . a pinion 38 , secured to input shaft 16 , is engaged with gear 40 and with gear 42 , which is secured to idler shaft 30 . gear 40 is supported on shaft 22 for rotation relative thereto . a pinion 44 , secured to input shaft 20 , is engaged with idler gear 46 , which is supported on idler shaft 30 for rotation relative to shaft 30 and is engaged with gear 48 , which is secured to layshaft 32 . a pinion 50 , which is supported on idler shaft 30 for rotation relative to shaft 30 , is engaged with gear 52 , which is supported on layshaft 32 for rotation relative to shaft 32 . second pairs of mutually engaged pinions and gears include gear 52 , engaged with gear 54 , which is secured to output shaft 26 . a pinion 56 , which is supported on layshaft 32 for rotation relative to shaft 32 , is engaged with gear 58 , which is secured to output shaft 26 . a pinion 60 , secured to layshaft 32 , is engaged with gear 62 , which is supported on output shaft 26 for rotation relative to shaft 26 . a reverse output gear 64 is supported on output shaft 26 for rotation relative to shaft 26 . a reverse idler gear ( not shown ) is continually meshing with pinion 60 and reverse output gear 64 , thereby providing an additional mesh so that the direction of rotation of gear 64 is opposite the direction of rotation of the other output gears 36 , 40 , 54 , 58 , 62 when reverse drive is selected . couplers 70 , 72 , 74 and 76 are preferably synchronizers of the type used in automotive manual transmissions to connect a gear or pinion to a shaft , after synchronizing the speed of the shaft and that of the pinion or gear . each coupler also disconnects the shaft and the associated pinion or gear . an example of such a synchronizer is disclosed in u . s . pat . no . 4 , 222 , 281 . alternatively , each coupler may be a toothed clutch having dogteeth that are engaged with clutch teeth on a gear or pinion . this invention may use couplers in any combination of synchronizers and dog clutches . each coupler is secured by a hub to a shaft . for example , coupler 70 is secured by hub 78 to output shaft 22 for rotation with output shaft 22 . in the case where a coupler is a synchronizer , it is provided with a conical surface 80 on a blocker ring , located adjacent the hub 78 and supported for axial displacement . the conical surface on each blocker ring engages with a corresponding conical surface 82 located on a gear 36 , 40 located adjacent the blocker ring . each synchronizer includes a sleeve 84 , supported on the hub 78 for axial displacement leftward and rightward from the positions shown in fig2 . when the sleeve 84 is displaced axially causing the synchronizer 70 to engage either of its adjacent gears 36 , 40 , the conical surface 80 on a blocker ring is forced into frictional contact with a conical surface 82 on the gear . this frictional engagement synchronizes the speed of the gear with that of the shaft 22 . when the rotational speeds of the shaft and gear are synchronized , further axial displacement of the sleeve 84 causes dog teeth on the radially inner surface of the sleeve to engage dog teeth carried on the adjacent gear . when the dog teeth of the sleeve engage those of the gear , the shaft 22 is driveably connected to the gear . in the case where a coupler is a dog clutch , displacement of the sleeve 84 in opposite axial directions causes mutual engagement of dog teeth formed on the sleeve with dog teeth carried on the gear , such that a drive connection is made between the shaft and the gear , but without first synchronizing the rotational speed of the shaft with the speed of the gear . in fig2 , the couplers 70 - 76 are shown in a neutral position , between the left - hand and right - hand extremities of travel of the connecting sleeve , whose engagement with dog teeth carried on the gear completes the drive connection to the shaft . the hubs of couplers 70 , 76 are rotatably secured to output shafts 22 and 26 , respectively ; the hub of coupler 72 is rotatably secured to idler shaft 30 ; the hub of coupler 74 is secured to layshaft 32 . coupler 70 , located between gears 36 , 40 , releasably connects alternately those gears to output shaft 22 , and coupler 70 may be disengaged from both gears 36 , 40 . coupler 74 , located between gears 52 , 56 , releasably connects alternately those gears to layshaft 32 , and coupler 74 disengages those gears from shaft 32 . coupler 76 , located between gears 62 , 64 , releasably connects alternately those gears to second output shaft 26 , and coupler 76 disengages those gears from shaft 26 . coupler 72 , located between gears 50 , 42 , releasably connects and disconnects only gear 50 and idler shaft 30 . to produce the first forward speed , clutch 18 is engaged , and the selector sleeve of coupler 76 is displaced leftward to connect gear 62 and output shaft 26 mutually . input 10 is driveably connected to shaft 20 through clutch 18 , causing pinion 44 to drive gear 48 and layshaft 32 through idler gear 46 . pinion 60 drives gear 62 , which is driveably connected to output shaft 26 through coupler 76 . output pinion 28 drives output 12 due to its engagement with output gear 25 . the second forward speed results by disengaging coupler 76 , sliding the selector sleeve of coupler 70 leftward to connect gear 36 to output shaft 22 , disengaging friction clutch 18 , and engaging clutch 14 . input 10 is driveably connected to input shaft 16 through clutch 14 , causing pinion 34 to drive gear 36 , which drives output shaft 22 through coupler 70 . output pinion 24 drives output 12 due to its engagement with output gear 25 . the third forward speed results by disengaging coupler 70 , sliding the selector sleeve of coupler 74 rightward to connect pinion 56 to layshaft 32 , disengaging friction clutch 14 , and engaging clutch 18 . input 10 is driveably connected to input shaft 20 through clutch 18 , causing pinion 44 to drive gear 48 and layshaft 32 through idler gear 46 . gear 48 drives layshaft 32 and pinion 56 through coupler 74 . pinion 56 drives gear 58 and output shaft 26 . output pinion 28 drives output 12 due to its engagement with output gear 25 . the fourth speed results by disengaging coupler 74 , sliding the selector sleeve of coupler 70 rightward to connect gear 40 to output shaft 22 , disengaging friction clutch 18 , and engaging clutch 14 . input 10 is driveably connected to input shaft 16 through clutch 14 , causing pinion 38 to drive gear 40 , which drives output shaft 22 through coupler 70 . output pinion 24 drives output 12 due to its engagement with output gear 25 . the fifth speed results by disengaging coupler 70 , sliding the selector sleeve of coupler 74 leftward to connect pinion 52 to layshaft 32 , disengaging friction clutch 14 , and engaging clutch 18 . input 10 is driveably connected to input shaft 20 through clutch 18 , causing pinion 44 to drive gear 48 and layshaft 32 through idler gear 46 . gear 48 drives layshaft 32 and pinion 52 through coupler 74 , and pinion 52 drives gear 54 and output shaft 26 . output pinion 28 drives output 12 due to its engagement with output gear 25 . the sixth speed results by disengaging coupler 74 , sliding the selector sleeve of coupler 72 leftward to connect pinion 50 to idler shaft 30 , disengaging friction clutch 18 , and engaging clutch 14 . input 10 is driveably connected to input shaft 16 through clutch 14 , causing pinion 38 to drive gear 42 , which drives idler shaft 30 and pinion 50 through coupler 72 . pinion 50 drives gear 54 through gear 52 , which , for sixth gear operation , functions as an idler . gear 54 drives output shaft 26 . output pinion 28 drives output 12 due to its engagement with output gear 25 . the output 12 is driven in the reverse direction by sliding the selector sleeve of coupler 76 rightward to connect gear 64 to output shaft 26 , and engaging friction clutch 18 . input 10 is driveably connected to input shaft 20 through clutch 18 , causing pinion 44 to drive gear 48 and layshaft 32 through idler 46 . pinion 60 is driveably connected to reverse output gear 64 , which drives output shaft 26 through coupler 76 . output pinion 28 drives output 12 due to its engagement with output gear 25 . refer now to the kinematic arrangement of the seven speed transmission of fig5 , which adds to the arrangement of fig2 a third pinion 90 secured to input shaft 16 , and a second forward drive gear 92 , supported on idler shaft 30 and engaged with the pinion 90 . the first forward drive gear 94 is supported on idler shaft 30 , but it is not secured to shaft 30 . the coupler 96 , which replaces coupler 72 , includes a hub that is secured to forward drive pinion 98 , rather than being secured to idler shaft 30 . moving the selector sleeve of coupler 96 rightward from the neutral position driveably connects pinion 98 and gear 94 ; moving that sleeve leftward driveably connects pinion 98 and idler shaft 30 . the first five forward speeds and reverse drive of the transmission of fig5 are produced identically as described with reference to fig2 . the sixth speed results by sliding the selector sleeve of coupler 96 rightward to connect pinion 98 and gear 94 , disengaging clutch 18 , and engaging clutch 14 . input 10 is driveably connected to input shaft 16 through clutch 14 , causing pinion 38 to drive gear 94 , which drives pinion 98 through coupler 96 . pinion 98 drives gear 54 through gear 52 , which , for sixth and seventh gear operation , functions as an idler . gear 54 drives output shaft 26 . output pinion 28 drives output 12 due to its engagement with output gear 25 . the seventh speed results by disengaging clutch 14 , sliding the selector sleeve of coupler 96 leftward to connect pinion 98 and idler shaft 30 , and re - engaging clutch 14 . input 10 is driveably connected to input shaft 16 through clutch 14 , causing pinion 90 to drive gear 92 , which drives idler shaft 30 due to gear 92 being secured to shaft 30 . coupler 96 driveably connects idler shaft 30 and pinion 98 , which drives gear 54 through idler gear 52 . gear 54 drives output shaft 26 . output pinion 28 drives output 12 due to its engagement with output gear 25 . an upshift from sixth to seventh gear , unlike all other single step shifts , requires a torque break , i . e ., the torsional connection between the input 10 and output 25 is briefly interrupted by disengaging clutch 14 while the state of coupler 96 is changed . this is mitigated because the 6 - 7 upshift is never made at high throttle ; instead , it usually occurs as a result of the driver reducing power demand when reaching cruising speed . downshifts inherently involve an output torque reduction , even for powershift transmissions , because some of the engine torque must be used to increase the engine speed . double step shifts , such as those from fifth gear to seventh gear , and from seventh gear to fifth gear can be performed without interrupting torque . in accordance with the provisions of the patent statutes , the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment . however , it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope .