Abstract:
An eight forward speed dual clutch transmission includes a pair of input clutches which selectively provide drive torque to a pair of concentric input shafts. Gears coupled to and driven by the input shafts are in constant mesh with gears freely rotatably disposed on a pair of parallel countershafts or layshafts. A plurality of synchronizer clutches selectively synchronize and connect the various gears to the countershafts or layshafts to provide a desired gear ratio in the proper sequence. Reverse gear is similarly provided through a three gear gear train. Upon the synchronization and engagement of a particular gear, the associated input clutch is activated or engaged to supply drive torque to the input shaft, through the synchronized and engaged gear pair and out the countershaft or layshaft. An additional gear on each countershaft or layshaft engages a common gear that directly drives a differential which, in turn, drives a pair of drive axles.

Description:
FIELD 
     The present disclosure relates to dual clutch transmissions and more particularly to eight speed dual clutch transmissions. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     Dual clutch transmissions are a relatively recent addition to the stable of motor vehicle transmissions which previously included manual, continuously variable and automatic transmissions. Dual clutch transmissions or DCT&#39;s as they are now commonly known, combine good fuel economy with rapidly executed shifts. From a performance standpoint, therefore, they closely duplicate the feel and operation of a conventional mechanical transmission. Additionally, they may be configured to operate as an essentially automatic or manual transmission and thus exhibit exceptional versatility. 
     Structurally, dual clutch transmissions typically include an input shaft which drives a pair of mutually exclusively engaged input clutches. The input clutches drive a pair of countershafts which each include a plurality of gears freely rotatably disposed on the countershafts and associated synchronizer clutches. The pluralities of gears are in constant mesh with gears secured to an output shaft. Activation of a synchronizer clutch synchronizes and couples a selected gear to its countershaft. Then, the input clutch associated with that countershaft is engaged to transmit torque from the input shaft to the output shaft. Because clutches, gears and synchronizers are disposed or stacked along the countershafts, the axial length of dual clutch transmissions can create packaging issues, particularly in smaller vehicles. 
     SUMMARY 
     The present invention provides three eight forward speed dual clutch transmissions especially adapted to front wheel drive (FWD) applications. A pair of input clutches selectively provide drive torque to a pair of concentric input shafts. A first plurality of gears coupled to and driven by the first input shaft are in constant mesh with gears freely rotatably disposed on a first parallel countershaft or layshaft and a second parallel countershaft or layshaft. A second plurality of gears coupled to and driven by the second input shaft are in constant mesh with gears freely rotatably disposed on the first countershaft or layshaft and the second countershaft or layshaft. The countershafts or layshafts essentially function as the output shafts of the transmission. A plurality of synchronizer clutches disposed on the countershafts or layshafts adjacent the gears selectively synchronize and connect the various gears to the countershafts or layshafts to provide a desired gear ratio. Reverse gear is similar and is provided through a gear train having three gears rather than two. Upon the synchronization and engagement of a particular gear to its countershaft or layshaft, the associated input clutch is activated or engaged to supply drive torque to the input shaft, through the synchronized and engaged gear pair and out the countershaft or layshaft. An additional gear on each countershaft or layshaft engages a common gear that directly drives a differential which, in turn, drives a pair of drive axles. 
     It is thus an aspect of the present invention to provide an eight forward speed dual clutch transmission. 
     It is a further aspect of the present invention to provide a dual clutch transmission having eight forward speeds or gear ratios and reverse. 
     It is a still further aspect of the present invention to provide a dual clutch transmission having a first clutch selectively driving a first input shaft and a second clutch selectively driving a second input shaft. 
     It is a still further aspect of the present invention to provide a dual clutch transmission having a first input shaft driving a plurality of gears, a plurality of gears on a first countershaft meshing with a respective one of said plurality of gears on the first input shaft and a plurality of gears on a second countershaft meshing with a respective one of said plurality of gears on the first input shaft. 
     It is a still further aspect of the present invention to provide a dual clutch transmission having a second input shaft driving a plurality of gears, a plurality of gears on a first countershaft meshing with a respective one of said plurality of gears on the second input shaft and a plurality of gears on a second countershaft meshing with a respective one of said plurality of gears on the second input shaft. 
     It is a still further aspect of the present invention to provide a dual clutch transmission having a plurality of freely rotating gears disposed on a first countershaft and a second countershaft. 
     It is a still further aspect of the present invention to provide a dual clutch transmission having a plurality of freely rotating gears disposed on a first countershaft and a second countershaft and a synchronizer clutch disposed adjacent the plurality of gears. 
     It is a still further aspect of the present invention to provide a dual clutch transmission having a gear driven by an input shaft, an idler gear meshing with the driven gear, a gear freely rotatably disposed on a countershaft and meshing with the idler gear and a synchronizer clutch disposed on the countershaft adjacent the freely rotatably disposed gear. 
     Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic plan layout of a first embodiment of an eight speed dual clutch transmission according to the present invention; 
         FIG. 2  is a schematic plan layout of a second embodiment of an eight speed dual clutch transmission according to the present invention; and 
         FIG. 3  is a schematic plan layout of a third embodiment of an eight speed dual clutch transmission according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     With reference now to  FIG. 1 , an eight forward speed or gear ratio dual clutch transmission is illustrated schematically and generally designated by the reference number  10 . The dual clutch transmission  10  includes a housing  12  which defines flanges, openings, bores, shoulders, recesses and the like which receive, support, enclose and protect the various components of the transmission  10 . The transmission  10  includes a main input shaft  14  which is driven by a gasoline, flex-fuel, Diesel, hybrid or electric engine, prime mover or power source. The main input shaft  14  drives a first input clutch  20  having one or more friction members  22  and a first actuator  24  which selectively drives a first input shaft or member  26 . The main input shaft  14  also drives a second input clutch  30  having one or more friction members  32  and a second actuator  34  which selectively drives a second input shaft, quill or member  36 . Preferably, the second input shaft, quill or member  36  is disposed concentrically about the first input shaft or member  26 . 
     The first input shaft or member  26  is also longer than the second input shaft, quill or member  36  and on its end opposite the first input clutch  20  are a first, larger drive gear  42 , an axially spaced apart second, intermediate size drive gear  44  and an axially spaced apart third, smaller drive gear  46  which are all coupled to and driven by the first input shaft or member  26 . 
     Disposed parallel to the axis of the first input shaft  26  and the second input member  36  are a first countershaft or layshaft  50  and a second countershaft or layshaft  60 . It will be appreciated that for reasons of clarity and explanation, the first and second countershafts or layshafts  50  and  60  have been rotated out of position and into the plane of  FIG. 1 . A first driven gear  52  is freely rotatably disposed on the first countershaft or layshaft  50  and is in constant mesh with the first, larger drive gear  42 . A second driven gear  54  is freely rotatably disposed on the first countershaft or layshaft  50  and is in constant mesh with the second, intermediate size drive gear  44 . A third driven gear  62  is freely rotatably disposed on the second countershaft or layshaft  60  and is in constant mesh with the first, larger drive gear  42 . A fourth driven gear  64  is freely rotatably disposed on the second countershaft or layshaft  60  and is in constant mesh with the third, smaller drive gear  46 . 
     A first double synchronizer clutch assembly  70  is disposed intermediate the first driven gear  52  and the second driven gear  54  and is rotationally coupled to the first countershaft or layshaft  50  by an interengaging spline set  72 . The output of a first three position actuator  74 , which may be hydraulic, electric or pneumatic, is connected to the first double synchronizer clutch assembly  70  through a shift fork (not illustrated) and selectively translates the first double synchronizer clutch assembly  70  between a first position in which it synchronizes and then connects the first driven gear  52  to the first countershaft or layshaft  50 , a second, middle or neutral position wherein no gear is connected to the first countershaft or layshaft  50  and a third position in which it synchronizes and then connects the second driven gear  54  to the first countershaft or layshaft  50 . 
     A second double synchronizer clutch assembly  80  is disposed intermediate the third driven gear  62  and the fourth driven gear  64  and is rotationally coupled to the second countershaft or layshaft  60  by an interengaging spline set  82 . The output of a second three position actuator  84 , which may be hydraulic, electric or pneumatic, is connected to the second double synchronizer clutch assembly  80  through a shift fork (not illustrated) and selectively translates the second double synchronizer clutch assembly  80  between a first position in which it synchronizes and then connects the third driven gear  62  to the second countershaft or layshaft  60 , a second, middle or neutral position wherein no gear is connected to the second countershaft or layshaft  60  and a third position in which it synchronizes and then connects the fourth driven gear  64  to the second countershaft or layshaft  60 . 
     In this configuration, the first embodiment, first gear (the highest speed reduction) is achieved by engagement of the fourth driven gear  64 , third gear is achieved by engagement of the second driven gear  54 , fifth gear is achieved by engagement of third driven gear  62  and seventh gear is achieved by engagement of first driven gear  52 . 
     The dual clutch transmission of the present invention includes a second, right portion (as illustrated in  FIG. 1 ) which provides even numbered gears and reverse and which is structurally and operationally similar to the first, left portion described directly above which provides odd numbered gears. Thus, on the second input shaft, quill or member  36  are a fourth, larger drive gear  92 , an axially spaced apart fifth, intermediate size drive gear  94  and an axially spaced apart sixth, smaller drive gear  96  which are all coupled to and driven by the second input shaft, quill or member  36 . 
     A fifth driven gear  102  is freely rotatably disposed on the first countershaft or layshaft  50  and is in constant mesh with the fourth, larger drive gear  92 . A sixth driven gear  104  is freely rotatably disposed on the first countershaft or layshaft  50  and is in constant mesh with the fifth, intermediate drive gear  94 . A seventh driven gear  106  is freely rotatably disposed on the first countershaft or layshaft  50  and is in constant mesh with the sixth, smaller drive gear  96 . 
     An eighth driven gear  112  is freely rotatably disposed on the second countershaft or layshaft  60  and is in constant mesh with the fourth, larger drive gear  92 . A ninth driven gear  114  is freely rotatably disposed on the second countershaft or layshaft  60  and is in constant mesh with the fifth, intermediate size drive gear  94 . A tenth driven gear  116  is freely rotatably disposed on the second countershaft or layshaft  60  and is in constant mesh with the seventh, driven gear  106  disposed on the first countershaft or layshaft  50 . The tenth driven gear  116 , since it is the final gear of a gear train comprising three gears ( 96 ,  106  and  116 ) rather than two, rotates in the opposite direction relative to the final (driven) gears of all the other gear trains and thus provides reverse. 
     A third double synchronizer clutch assembly  120  is disposed intermediate the fifth driven gear  102  and the sixth driven gear  104  and is rotationally coupled to the first countershaft or layshaft  50  by an interengaging spline set  122 . The output of a third three position actuator  124 , which may be hydraulic, electric or pneumatic, is connected to the third double synchronizer clutch assembly  120  through a shift fork (not illustrated) and selectively translates the third double synchronizer clutch assembly  120  between a first position in which it synchronizes and then connects the fifth driven gear  102  to the first countershaft or layshaft  50 , a second, middle or neutral position wherein no gear is connected to the first countershaft or layshaft  50  and a third position in which it synchronizes and then connects the sixth driven gear  104  to the first countershaft or layshaft  50 . 
     A fourth double synchronizer clutch assembly  130  is disposed intermediate the eighth driven gear  112  and the ninth driven gear  114  and is rotationally coupled to the second countershaft or layshaft  60  by an interengaging spline set  132 . The output of a fourth three position actuator  134 , which may be hydraulic, electric or pneumatic, is connected to the fourth double synchronizer clutch assembly  130  through a shift fork (not illustrated) and selectively translates the second double synchronizer clutch assembly  130  between a first position in which it synchronizes and then connects the eighth driven gear  112  to the second countershaft or layshaft  60 , a second, middle or neutral position wherein no gear is connected to the second countershaft or layshaft  60  and a third position in which it synchronizes and then connects the ninth driven gear  114  to the second countershaft or layshaft  60 . 
     A fifth synchronizer clutch assembly  140 , which is a single clutch and synchronizer assembly, is disposed adjacent the tenth driven gear  116  and is rotationally coupled to the second countershaft or layshaft  60  by an interengaging spline set  142 . The output of a two position actuator  144 , which may be hydraulic, electric or pneumatic, is connected to the fifth synchronizer clutch assembly  140  through a shift fork (not illustrated) and selectively translates the fifth synchronizer clutch assembly  140  between a first position in which it synchronizes and then connects the tenth driven gear  116  to the second countershaft or layshaft  60  and a second, neutral position wherein the tenth driven gear  116  is free to rotate on the second countershaft or layshaft  60 . 
     In this configuration, the first embodiment, second gear is achieved by engagement of the ninth driven gear  114 , fourth gear is achieved by engagement of the sixth driven gear  104 , sixth gear is achieved by engagement of the eighth driven gear  112 , eighth gear is achieved by engagement of the fifth driven gear  102  and reverse is achieved by engagement of the tenth driven gear  116 . 
     Coupled to the first countershaft or layshaft  50  and the second countershaft or layshaft  60  and in alignment along the axes of the first countershaft or layshaft  50  and the second countershaft or layshaft  60  are, respectively, a first output gear  152  and a second output gear  154 . The output gears  152  and  154  are both in constant mesh with a ring gear  156  which is disposed about and directly drives a cage or housing  158  of a differential assembly  160 . The differential assembly  160  includes a pair of opposed idler gears  162  and a constantly meshed pair of output gears  164  that are coupled to and drive a respective pair of axles  166 . 
     Referring now to  FIG. 2 , a second embodiment of an eight speed dual clutch transmission according to the present invention is illustrated and generally designated by the reference number  200 . The dual clutch transmission  200  includes a housing  212  which defines flanges, openings, bores, shoulders, recesses and the like which receive, support, enclose and protect the various components of the transmission  200 . The transmission  200  includes a main input shaft  214  which is driven by a gasoline, flex-fuel, Diesel, hybrid or electric engine, prime mover or power source. The main input shaft  214  drives a first input clutch  220  having one or more friction members  222  and a first actuator  224  which selectively drives a first input shaft or member  226 . The main input shaft  214  also drives a second input clutch  230  having one or more friction members  232  and a second actuator  234  which selectively drives a second input shaft, quill or member  236 . Preferably, the second input shaft, quill or member  236  is disposed concentrically about the first input shaft or member  226 . 
     The first input shaft or member  226  is longer than the second input shaft, quill or member  236  and on its end opposite the first input clutch  220  are a first, smaller drive gear  242  and an axially spaced apart second, larger drive gear  244  which are both coupled to and driven by the first input shaft or member  226 . 
     Disposed parallel to the axis of the first input shaft  226  and the second input member  236  are a first countershaft or layshaft  250  and a second countershaft or layshaft  260 . As presented in  FIG. 1 , the first and second countershafts or layshafts  250  and  260  have been rotated out of position and into the plane of  FIG. 2  for reasons of clarity and explanation. A first, larger driven gear  252  is freely rotatably disposed on the first countershaft or layshaft  250  and is in constant mesh with the first, smaller drive gear  242 . A second, smaller driven gear  254  is freely rotatably disposed on the first countershaft or layshaft  250  and is in constant mesh with the second, larger drive gear  244 . A third, larger driven gear  262  is freely rotatably disposed on the second countershaft or layshaft  260  and is in constant mesh with the first, smaller drive gear  242 . A fourth, smaller driven gear  264  is freely rotatably disposed on the second countershaft or layshaft  260  and is in constant mesh with the second, larger drive gear  244 . 
     A first double synchronizer clutch assembly  270  is disposed intermediate the first, larger driven gear  252  and the second, smaller driven gear  254  and is rotationally coupled to the first countershaft or layshaft  250  by an interengaging spline set  272 . The output of a first three position actuator  274 , which may be hydraulic, electric or pneumatic, is connected to the first double synchronizer clutch assembly  270  through a shift fork (not illustrated) and selectively translates the first double synchronizer clutch assembly  270  between a first position in which it synchronizes and then connects the first, larger driven gear  252  to the first countershaft or layshaft  250 , a second, middle or neutral position wherein no gear is connected to the first countershaft or layshaft  250  and a third position in which it synchronizes and then connects the second, smaller driven gear  254  to the first countershaft or layshaft  250 . 
     A second double synchronizer clutch assembly  280  is disposed intermediate the third, larger driven gear  262  and the fourth, smaller driven gear  264  and is rotationally coupled to the second countershaft or layshaft  260  by an interengaging spline set  282 . The output of a second three position actuator  284 , which may be hydraulic, electric or pneumatic, is connected to the second double synchronizer clutch assembly  280  through a shift fork (not illustrated) and selectively translates the second double synchronizer clutch assembly  280  between a first position in which it synchronizes and then connects the third, larger driven gear  262  to the second countershaft or layshaft  260 , a second, middle or neutral position wherein no gear is connected to the second countershaft or layshaft  260  and a third position in which it synchronizes and then connects the fourth, smaller driven gear  264  to the second countershaft or layshaft  260 . 
     In this configuration, the second embodiment transmission  200 , first gear (the highest speed reduction) is achieved by engagement of the third, larger driven gear  262 , third gear is achieved by engagement of the first, larger driven gear  252 , fifth gear is achieved by engagement of fourth, smaller driven gear  264  and seventh gear is achieved by engagement of second, smaller driven gear  254 . 
     The dual clutch transmission of the present invention includes a second, right portion (as illustrated in  FIG. 2 ) which provides even numbered gears and reverse and which is structurally and operationally similar to the first, left portion described directly above which provides odd numbered gears. Thus, on the second input shaft, quill or member  236  are a third, intermediate size drive gear  292 , an axially spaced apart fourth, intermediate size drive gear  294 , an axially spaced apart fifth, larger drive gear  296  and an axially spaced apart sixth, smaller drive gear  298  which are all coupled to and driven by the second input shaft, quill or member  236 . 
     A fifth driven gear  302  is freely rotatably disposed on the first countershaft or layshaft  250  and is in constant mesh with the third, intermediate size drive gear  292 . A sixth driven gear  304  is freely rotatably disposed on the first countershaft or layshaft  250  and is in constant mesh with the fifth, larger drive gear  296 . A seventh driven gear  306  is freely rotatably disposed on the first countershaft or layshaft  250 . 
     An eighth driven gear  312  is freely rotatably disposed on the second countershaft or layshaft  260  and is in constant mesh with the fourth, intermediate size drive gear  294 . A ninth driven gear  314  is freely rotatably disposed on the second countershaft or layshaft  260  and is in constant mesh with the sixth, smaller drive gear  298  and the seventh driven gear  306 . The seventh driven gear  306 , since it is the final gear of a gear train comprising three gears ( 298 ,  314  and  306 ) rather than two, rotates in the opposite direction relative to the driven gears of all the other gear trains and thus provides reverse. 
     A third synchronizer clutch assembly  320 , which is a single clutch and synchronizer assembly, is disposed adjacent the fifth driven gear  302  and is rotationally coupled to the first countershaft or layshaft  250  by an interengaging spline set  322 . The output of a first two position actuator  324 , which may be hydraulic, electric or pneumatic, is connected to the third synchronizer clutch assembly  320  through a shift fork (not illustrated) and selectively translates the third synchronizer clutch assembly  320  between a first position in which it synchronizes and then connects the fifth driven gear  302  to the first countershaft or layshaft  250  and a second, neutral position wherein the fifth driven gear  302  is free to rotate on the first countershaft or layshaft  250 . 
     A fourth double synchronizer clutch assembly  330  is disposed intermediate the sixth driven gear  304  and the seventh driven gear  306  and is rotationally coupled to the first countershaft or layshaft  250  by an interengaging spline set  332 . The output of a fourth three position actuator  334 , which may be hydraulic, electric or pneumatic, is connected to the fourth double synchronizer clutch assembly  330  through a shift fork (not illustrated) and selectively translates the fourth double synchronizer clutch assembly  330  between a first position in which it synchronizes and then connects the sixth driven gear  304  to the first countershaft or layshaft  250 , a second, middle or neutral position wherein no gear is connected to the first countershaft or layshaft  250  and a third position in which it synchronizes and then connects the seventh driven gear  306  to the first countershaft or layshaft  250 . 
     A fifth double synchronizer clutch assembly  340  is disposed intermediate the eighth driven gear  312  and the ninth driven gear  314  and is rotationally coupled to the second countershaft or layshaft  260  by an interengaging spline set  342 . The output of a fifth three position actuator  344 , which may be hydraulic, electric or pneumatic, is connected to the fourth double synchronizer clutch assembly  340  through a shift fork (not illustrated) and selectively translates the fifth double synchronizer clutch assembly  340  between a first position in which it synchronizes and then connects the eighth driven gear  312  to the second countershaft or layshaft  260 , a second, middle or neutral position wherein no gear is connected to the second countershaft or layshaft  260  and a third position in which it synchronizes and then connects the ninth driven gear  314  to the second countershaft or layshaft  260 . 
     In this configuration, the second embodiment transmission  200 , second gear is achieved by engagement of the ninth driven gear  314 , fourth gear is achieved by engagement of the fifth driven gear  302 , sixth gear is achieved by engagement of the eighth driven gear  312 , eighth gear is achieved by engagement of the sixth driven gear  304  and reverse is achieved by engagement of the seventh driven gear  306 . 
     Coupled to the first countershaft or layshaft  250  and the second countershaft or layshaft  260  and in alignment along the axes of the first countershaft or layshaft  250  and the second countershaft or layshaft  260  are, respectively, a first output gear  352  and a second output gear  354 . The output gears  352  and  354  are both in constant mesh with a ring gear  356  which is disposed about and directly drives a cage or housing  358  of a differential assembly  360 . The differential assembly  360  includes a pair of opposed idler gears  362  and a constantly meshed pair of output gears  364  that are coupled to and drive a respective pair of axles  366 . 
     Referring now to  FIG. 3 , a third embodiment of an eight speed dual clutch transmission according to the present invention is illustrated and generally designated by the reference number  400 . The dual clutch transmission  400  includes a housing  412  which defines flanges, openings, bores, shoulders, recesses and the like which receive, support, enclose and protect the various components of the transmission  400 . The transmission  400  includes a main input shaft  414  which is driven by a gasoline, flex-fuel, Diesel, hybrid or electric engine, prime mover or power source. The main input shaft  414  drives a first input clutch  420  having one or more friction members  422  and a first actuator  424  which selectively drives a first input shaft or member  426 . The main input shaft  414  also drives a second input clutch  430  having one or more friction members  432  and a second actuator  434  which selectively drives a second input shaft, quill or member  436 . Preferably, the second input shaft, quill or member  436  is disposed concentrically about the first input shaft or member  426 . 
     The first input shaft or member  426  is longer than the second input shaft, quill or member  436  and on its end opposite the first input clutch  420  are a first, smaller drive gear  442  and an axially spaced apart second, larger drive gear  444  which are both coupled to and driven by the first input shaft or member  426 . 
     Disposed parallel to the axis of the first input shaft  426  and the second input member  436  are a first countershaft or layshaft  450  and a second countershaft or layshaft  460 . As they were presented in  FIG. 1 , the first and second countershafts or layshafts  450  and  460  have been rotated out of position and into the plane of  FIG. 3  for reasons of clarity and explanation. A first, larger driven gear  452  is freely rotatably disposed on the first countershaft or layshaft  450  and is in constant mesh with the first, smaller drive gear  442 . A second, smaller driven gear  454  is freely rotatably disposed on the first countershaft or layshaft  450  and is in constant mesh with the second, larger drive gear  444 . A third, larger driven gear  462  is freely rotatably disposed on the second countershaft or layshaft  460  and is in constant mesh with the first, smaller drive gear  442 . A fourth, smaller driven gear  464  is freely rotatably disposed on the second countershaft or layshaft  460  and is in constant mesh with the second, larger drive gear  444 . 
     A first double synchronizer clutch assembly  470  is disposed intermediate the first, larger driven gear  452  and the second, smaller driven gear  454  and is rotationally coupled to the first countershaft or layshaft  450  by an interengaging spline set  472 . The output of a first three position actuator  474 , which may be hydraulic, electric or pneumatic, is connected to the first double synchronizer clutch assembly  470  through a shift fork (not illustrated) and selectively translates the first double synchronizer clutch assembly  470  between a first position in which it synchronizes and then connects the first, larger driven gear  452  to the first countershaft or layshaft  450 , a second, middle or neutral position wherein no gear is connected to the first countershaft or layshaft  450  and a third position in which it synchronizes and then connects the second, smaller driven gear  454  to the first countershaft or layshaft  450 . 
     A second double synchronizer clutch assembly  480  is disposed intermediate the third, larger driven gear  462  and the fourth, smaller driven gear  464  and is rotationally coupled to the second countershaft or layshaft  460  by an interengaging spline set  482 . The output of a second three position actuator  484 , which may be hydraulic, electric or pneumatic, is connected to the second double synchronizer clutch assembly  480  through a shift fork (not illustrated) and selectively translates the second double synchronizer clutch assembly  480  between a first position in which it synchronizes and then connects the third, larger driven gear  462  to the second countershaft or layshaft  460 , a second, middle or neutral position wherein no gear is connected to the second countershaft or layshaft  460  and a third position in which it synchronizes and then connects the fourth, smaller driven gear  464  to the second countershaft or layshaft  460 . 
     In this configuration, the third embodiment transmission  400 , first gear (the highest speed reduction) is achieved by engagement of the third, larger driven gear  462 , third gear is achieved by engagement of the first, larger driven gear  452 , fifth gear is achieved by engagement of fourth, smaller driven gear  464  and seventh gear is achieved by engagement of second, smaller driven gear  454 . 
     The dual clutch transmission of the present invention includes a second, right portion (as illustrated in  FIG. 3 ) which provides even numbered gears and reverse and which is structurally and operationally similar to the first, left portion described directly above which provides odd numbered gears. Thus, on the second input shaft, quill or member  436  are a third, intermediate size drive gear  492 , an axially spaced apart fourth, larger drive gear  494  and an axially spaced apart fifth, smaller drive gear  496  which are all coupled to and driven by the second input shaft, quill or member  436 . 
     A fifth driven gear  502  is freely rotatably disposed on the first countershaft or layshaft  450  and is in constant mesh with the third, intermediate size drive gear  492 . A sixth driven gear  504  is freely rotatably disposed on the first countershaft or layshaft  450  and is in constant mesh with the fifth, larger drive gear  496 . A seventh driven gear  506  is freely rotatably disposed on the first countershaft or layshaft  450 . 
     An eighth driven gear  512  is freely rotatably disposed on the second countershaft or layshaft  460  and is in constant mesh with the fourth intermediate size drive gear  494 . A ninth driven gear  514  is freely rotatably disposed on the second countershaft or layshaft  460  and is in constant mesh with the fifth, smaller drive gear  496  and the seventh driven gear  506 . The seventh driven gear  506 , since it is the final gear of a gear train comprising three gears ( 496 ,  514  and  506 ) rather than two, rotates in the opposite direction relative to all the driven gears of all the other gear trains and thus provides reverse. 
     A third synchronizer clutch assembly  520 , which is a single clutch and synchronizer assembly, is disposed adjacent the fifth driven gear  502  and is rotationally coupled to the first countershaft or layshaft  450  by an interengaging spline set  522 . The output of a first two position actuator  524 , which may be hydraulic, electric or pneumatic, is connected to the third synchronizer clutch assembly  520  through a shift fork (not illustrated) and selectively translates the third synchronizer clutch assembly  520  between a first position in which it synchronizes and then connects the fifth driven gear  502  to the first countershaft or layshaft  450  and a second, neutral position wherein the fifth driven gear  502  is free to rotate on the first countershaft or layshaft  450 . 
     A fourth double synchronizer clutch assembly  530  is disposed intermediate the sixth driven gear  504  and the seventh driven gear  506  and is rotationally coupled to the first countershaft or layshaft  450  by an interengaging spline set  532 . The output of a fourth three position actuator  534 , which may be hydraulic, electric or pneumatic, is connected to the fourth double synchronizer clutch assembly  530  through a shift fork (not illustrated) and selectively translates the fourth double synchronizer clutch assembly  530  between a first position in which it synchronizes and then connects the sixth driven gear  504  to the first countershaft or layshaft  450 , a second, middle or neutral position wherein no gear is connected to the first countershaft or layshaft  450  and a third position in which it synchronizes and then connects the seventh driven gear  506  to the first countershaft or layshaft  450 . 
     A fifth double synchronizer clutch assembly  540  is disposed intermediate the eighth driven gear  512  and the ninth driven gear  514  and is rotationally coupled to the second countershaft or layshaft  460  by an interengaging spline set  542 . The output of a fifth three position actuator  544 , which may be hydraulic, electric or pneumatic, is connected to the fourth double synchronizer clutch assembly  540  through a shift fork (not illustrated) and selectively translates the fifth double synchronizer clutch assembly  540  between a first position in which it synchronizes and then connects the eighth driven gear  512  to the second countershaft or layshaft  460 , a second, middle or neutral position wherein no gear is connected to the second countershaft or layshaft  460  and a third position in which it synchronizes and then connects the ninth driven gear  514  to the second countershaft or layshaft  460 . 
     In this configuration, the third embodiment  400 , second gear is achieved by engagement of the ninth driven gear  514 , fourth gear is achieved by engagement of the fifth driven gear  502 , sixth gear is achieved by engagement of the eighth driven gear  512 , eighth gear is achieved by engagement of the sixth driven gear  504  and reverse is achieved by engagement of the seventh driven gear  506 . 
     Coupled to the first countershaft or layshaft  450  and the second countershaft or layshaft  460  and in alignment along the axes of the first countershaft or layshaft  450  and the second countershaft or layshaft  460  are, respectively, a first output gear  552  and a second output gear  554 . The output gears  552  and  554  are both in constant mesh with a ring gear  556  which is disposed about and directly drives a cage or housing  558  of a differential assembly  560 . The differential assembly  560  includes a pair of opposed idler gears  562  and a constantly meshed pair of output gears  564  that are coupled to and drive a respective pair of axles  566 . 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.