Abstract:
In a transmission with a first clutch including a first upstream rotary member to be driven by an input shaft, and a first downstream rotary member to be driven by the first upstream rotary member to drive an output shaft so that the first upstream and downstream rotary members are adapted to be selectively engaged with each other and disengaged from each other, an output shaft driving device includes a second upstream rotary member to be driven by the input shaft, and a second downstream rotary member to be driven by the second upstream rotary member to drive the output shaft.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT  
         [0001]    The present invention relates to a transmission for transmitting a torque from an input shaft to an output shaft.  
           [0002]    JP-A-11-264449 discloses a transmission including coaxial input and output shafts, a bypass torque path for transmitting a torque from the input shaft to the output shaft through a intermediate shaft extending parallel to the coaxial input and output shafts and two gear trains, and a pair of input clutches one of which transmits the torque from the input shaft to the output shaft through selected one of gear pairs of respective shift stages, and another one of which transmits the torque from the input shaft to the output shaft without changing a rotational speed between the input and output shafts.  
           [0003]    JP-A-61-45163 discloses a transmission in which a torque is transmitted from an input shaft to an output shaft during a shifting operation through the last shift stage (smallest reduction ratio shift stage) gear pair.  
         OBJECT AND SUMMARY OF THE INVENTION  
         [0004]    An object of the present invention is to provide a transmission in which an engage and/or disengage between an input shaft and an output shaft can be carried out while restraining an abrupt change in torque transmitted therebetween.  
           [0005]    In a transmission comprising, an input shaft, an output shaft, and a first clutch including a first upstream rotary member rotationally connected to the input shaft to be driven by the input shaft, and a first downstream rotary member to be driven by the first upstream rotary member and rotationally connected to the output shaft to drive the output shaft and to be driven by the output shaft, wherein the first upstream and downstream rotary members are adapted to be selectively engaged with each other and disengaged from each other, the transmission further comprises, an output shaft driving device for applying a torque to the output shaft at least when the first upstream and downstream rotary members are disengaged from each other. The output shaft driving device may includes a second upstream rotary member to be driven by the input shaft and a second downstream rotary member to be driven by the second upstream rotary member to drive the output shaft so that the torque transmitted by the output shaft driving device from the second upstream rotary member to the second downstream rotary member is variably adjustable by changing a slipping or attracting degree (torque transmitting degree) between the second upstream and downstream rotary members when a rotational speed of the output shaft is smaller than that of the input shaft, or the output shaft driving device may be an electric motor for applying the torque to the output shaft.  
           [0006]    By the output shaft driving device, an engage and/or disengage through the first clutch between the input shaft and the output shaft can be carried out while restraining an abrupt change in torque transmitted therebetween.  
           [0007]    It is preferable for restraining the abrupt change in torque transmitted between the output and input shafts that the first upstream and downstream rotary members are disengaged from each other after the torque applied by the output shaft driving device to drive the output shaft is gradually increased, that the torque transmitted by the output shaft driving device to drive the output shaft is decreased after the first upstream and downstream rotary members are engaged with each other, that the torque applied by the output shaft driving device to the output shaft is adjusted in such a manner that a difference in rotational speed between the first upstream and downstream rotary members is kept within a predetermined range just before the first upstream and downstream rotary members are engaged with each other, and/or that the torque applied by the output shaft driving device to the output shaft is adjusted in such a manner that a difference in rotational speed between the first upstream and downstream rotary members just after the first upstream and downstream rotary members are disengaged from each other is kept within a predetermined range (a difference between the torque applied by the output shaft driving device just after the first upstream and downstream rotary members are disengaged from each other and the torque transmitted between the input shaft and the output shaft just before the first upstream and downstream rotary members are disengaged from each other is kept within a predetermined range).  
           [0008]    When the transmission further comprises, a counter shaft through which the first clutch is rotationally connected to the output shaft to be driven by the input shaft so that the first upstream rotary member is driven by the input shaft, the first downstream rotary member is driven by the first upstream rotary member to drive the output shaft through the counter shaft, and the first downstream rotary member is driven by the output shaft through the counter shaft, a pair of first and second gears, the first gear being adapted to be driven by the counter shaft, the second gear being adapted to be driven by the first gear to drive the output shaft, and the first and second gears mating with each other, and a second clutch including a second shaft-side rotary member rotationally fixed to one of the counter shaft and the output shaft, and a second gear-side rotary member rotationally fixed to one of the first and second gears in such a manner that the input shaft is permitted to be rotationally connected to the output shaft through the second shaft-side and gear-side rotary members and the pair of first and second gears, so that the second shaft-side rotary member is adapted to be selectively engaged with the second gear-side rotary member and disengaged from the second gear-side rotary member,  
           [0009]    it is preferable for restraining the abrupt change in torque transmitted between the output and input shafts that the torque applied by the output shaft driving device to the output shaft is adjusted in such a manner that a difference in rotational speed between the second shaft-side and gear-side rotary members obtainable when the first upstream and downstream rotary members are engaged with each other is kept within a predetermined range just before the second shaft-side and gear-side rotary members are engaged with each other, that the torque applied by the output shaft driving device to the output shaft is adjusted in such a manner that a difference in rotational speed between the second shaft-side and gear-side rotary members just after the second shaft-side and gear-side rotary members are disengaged from each other is kept within a predetermined range (a difference between the torque applied by the output shaft driving device just after the second shaft-side and gear-side rotary members are disengaged from each other and the torque transmitted between the input shaft and the output shaft just before the second shaft-side and gear-side rotary members are disengaged from each other is within a predetermined range is kept within a predetermined range), that the torque applied by the output shaft driving device to the output shaft is adjusted in such a manner that a difference in rotational speed between the first upstream and downstream rotary members obtained after the second shaft-side rotary member is engaged with the second gear-side rotary member is kept within a predetermined range just before the first upstream and downstream rotary members are engaged with each other, that the second shaft-side rotary member is disengaged from the second gear-side rotary member after the first upstream and downstream rotary members are disengaged from each other, that the torque applied by the output shaft driving device to the output shaft is gradually increased before the second shaft-side rotary member is disengaged from the second gear-side rotary member, and/or that the torque applied by the output shaft driving device to the output shaft is decreased after the first upstream and downstream rotary members are engaged with each other while the second shaft-side rotary member is kept engaged with the second gear-side rotary member.  
           [0010]    When the transmission further comprises, another pair of first and second gears, the first gear being adapted to be driven by the counter shaft, the second gear being adapted to be driven by the first gear to drive the output shaft, the first and second gears mating with each other, and a reduction gear ratio of the pair of first and second gears being larger than that of the another pair of first and second gears, and a third clutch including a third shaft-side rotary member rotationally fixed to one of the counter shaft and the output shaft, and a third gear-side rotary member rotationally fixed to one of the first and second gears of the another pair so that the input shaft is rotationally connected to the output shaft through the third shaft-side and gear-side rotary members and the another pair of first and second gears, wherein the third shaft-side rotary member is adapted to be selectively engaged with the third gear-side rotary member and disengaged from the third gear-side rotary member, and the second clutch and third clutch are cooperative in such a manner that the third shaft-side rotary member is engaged with the third gear-side rotary member when the second shaft-side rotary member is disengaged from the second gear-side rotary member and the third shaft-side rotary member is disengaged from the third gear-side rotary member when the second shaft-side rotary member is engaged with the second gear-side rotary member,  
           [0011]    it is preferable for restraining the abrupt change in torque transmitted between the output and input shafts that the torque applied by the output shaft driving device to the output shaft is gradually increased before the third shaft-side rotary member is engaged with the third gear-side rotary member after the second shaft-side rotary member is disengaged from the second gear-side rotary member, and/or that the torque applied by the output shaft driving device to the output shaft is adjusted in such a manner that a difference in rotational speed between the third shaft-side rotary member and the third gear-side rotary member obtainable when the first upstream and downstream rotary members are engaged with each other is kept within a predetermined range just before the third shaft-side rotary member is engaged with the third gear-side rotary member.  
           [0012]    A peripheral total number of teeth of the first gear of the another pair may be smaller than that of the second gear of the another pair so that a rotational speed of the output shaft is lower than that of the input shaft.  
           [0013]    When a peripheral total number of teeth of the first gear of the another pair is larger than that of the second gear of the another pair so that a rotational speed of the output shaft is higher than that of the input shaft, it is preferable for restraining the abrupt change in torque transmitted between the output and input shafts that the output shaft driving device includes a one-way clutch for transmitting the torque through the output shaft driving device when the rotational speed of the output shaft is lower than that of the input shaft and preventing the torque from being transmitted through the output shaft driving device when the rotational speed of the output shaft is higher than that of the input shaft.  
           [0014]    It is preferable for speedy rotational speed control of the counter shaft that the first upstream and downstream rotary members are engaged temporarily with each other to decrease a difference in rotational speed between the first upstream and downstream rotary members while increasing the torque applied by the output shaft driving device to the output shaft, before the third shaft-side and gear-side rotary members are engaged with each other after the second shaft-side rotary member is disengaged from the second gear-side rotary member after the first upstream and downstream rotary members are disengaged from each other.  
           [0015]    It is preferable that a radial inside of at least a part of the counter shaft while being prevented from including a gear train between the output shaft driving device and the output shaft. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a view schematically showing an embodiment of the present invention;  
         [0017]    [0017]FIG. 2 is a view showing in details a first clutch C 1  and a second clutch C 2  in the embodiment shown in FIG. 1;  
         [0018]    [0018]FIG. 3 is a flow chart of a shift up operation in the embodiment shown in FIG. 1;  
         [0019]    [0019]FIG. 4 is a diagram showing variations in torque transmitted by the first and second clutches during a shift operation in the embodiment shown in FIG. 1;  
         [0020]    [0020]FIG. 5 is a diagram showing variations in rotational speeds of transmission output shaft and engine output shaft, and a variation of an imaginarily calculated first input shaft rotational speed;  
         [0021]    [0021]FIG. 6 is a view showing a torque variation of the transmission output shaft during the shift operation in the embodiment shown in FIG. 1;  
         [0022]    [0022]FIG. 7 is a view schematically showing another embodiment of the present invention;  
         [0023]    [0023]FIG. 8 is a view schematically showing another embodiment of the present invention;  
         [0024]    [0024]FIG. 9 is a view schematically showing another embodiment of the present invention;  
         [0025]    [0025]FIG. 10 is a view schematically showing another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]    [0026]FIG. 1 is a view schematically showing an embodiment of a four-shift-stages transmission as an example of the invention.  
         [0027]    In FIG. 1, a drive source  1  is an engine. A first clutch C 1  and a second clutch C 2  are connected to an output shaft SE of the drive source  1 . An input shaft of a transmission  2  include a first input shaft S 1  and a second input shaft S 2  connected respectively through the first clutch C 1  and the second clutch C 2  to the output shaft SE. The first input shaft S 1  has a hollow shape, the second input shaft S 2  is arranged at a radial inside of the first input shaft S 1  or surrounded by the first input shaft S 1 , and the first input shaft S 1  is connected to the first clutch C 1 . The second input shaft S 2  is connected to the second clutch C 2 .  
         [0028]    In this case, in FIG. 1, a mechanism for operating the respective clutches is not illustrated, however, an engaging and disengaging operation can be executed by an external operation.  
         [0029]    That is, when the first clutch C 1  is engaged, a torque output from the output shaft SE of the drive source  1  is transmitted to the first input shaft S 1  of the transmission, and when the second clutch C 2  is engaged, the torque output from the output shaft SE of the drive source  1  is transmitted to the second input shaft S 2  of the transmission.  
         [0030]    The transmission  2  is a synchromesh transmission similar to a conventional transmission for a manual shift, and is differentiated therefrom by the second input shaft S 2  directly connected to a transmission output shaft SO through a joint portion J 1  without any gear train between the second clutch C 2  and the transmission output shaft SO. FIG. 1 is a transmission mechanism shiftable between a first shift stage and a fourth shift stage.  
         [0031]    The transmission  2  includes the first input shaft S 1 , the second input shaft S 2 , a counter shaft SC, the transmission output shaft SO, a plurality of shift-stage pairs of gears mounted respectively onto the transmission output shaft SO and the counter shaft SC in each pair, and a first gear shift clutch SC 1  and a second gear shift clutch SC 2  for changing a torque transmitting path in accordance with a desired shift stage.  
         [0032]    The counter shaft SC is rotated by a torque transmitted from the first input shaft S 1  through a counter drive gear DC to a counter driven gear GC. Further, a first shift stage drive gear D 1  and a first shift stage driven gear G 1  are used for the first shift stage, a second shift stage drive gear D 2  and a second shift stage driven gear G 2  are used for a second shift stage and a third shift stage drive gear D 3  and a third shift stage driven gear G 3  are used for a third shift stage, between the counter shaft SC and the transmission output shaft SO. Each of the driven gears G 1 - 3  is rotatable on the transmission output shaft. Each of the drive gear D 1 - 3  is fixed to the counter shaft SC. Each of the first gear shift clutch SC 1  and the second gear shift clutch SC 2  is used to fix rotationally one of the driven gears G 1 - 3  and spline H 4  to the transmission output shaft. Sleeves  31  and  32  movable in an axial direction respectively on the hubs  41  and  42  while being rotationally fixed to respectively the hubs  41  and  42  are provided within the respective gear shift clutches SC 1  and SC 2 , and splines are formed in the sleeves  31  and  32  respectively. The splines engage respectively with the hubs  41  and  42  fixed to the transmission output shaft so as to transmit the torque. Other splines are formed on the driven gears, and in the case that the sleeves are at neutral positions, the sleeves  31  and  32  are not in an engaging state with the splines H 1 , H 2  and H 3  of the driven gears and the spline H 4  of the first input shaft, so that the driven gears and the first input shaft are freely rotatable with respect to the transmission output shaft. When moving the sleeve in the axial direction, one of the splines H 1 , H 2  and H 3  of the driven gears or the spline H 4  of the first input shaft engages with the spline on the sleeve  31  or  32  while the sleeve engages with the hub  41  or  42 , so that one of the driven gears or the first input shaft is fixed rotationally to the transmission output shaft. Further, a synchromesh mechanism for synchronizing the rotations of the one of the splines H 1 , H 2  and H 3  of the driven gears or the spline H 4  of the first input shaft and the spline on the sleeve  31  or  32  when a difference in rotational speed therebetween is exists may be assembled in the gear shift clutch. Further, a mechanism for moving the sleeves is not illustrated.  
         [0033]    When the shift stage is changed, the sleeve  31  of the first gear shift clutch SC 1  or the sleeve  32  of the second gear shift clutch SC 2  is operated so as to be engaged with the one of the spline H 1 , H 2  and H 3  of the first input shaft or the spline H 4  of the first input shaft in accordance with the desired shift stage, so that the selected driven gear or the first input shaft is fixed rotationally to the transmission output shaft So, whereby a torque transmission path is formed. In the fourth shift stage, the spline H 4  for the fourth shift stage is directly connected to the first input shaft S 1 , so that the first input shaft S 1  and the transmission output shaft SO are directly connected to each other without any gear train.  
         [0034]    Although the driven gear on the transmission output shaft SO is equipped with the gear shift clutch in the above case, at least one of the first gear shift clutch SC 1  and the second gear shift clutch SC 2  may be mounted on the drive gear on the counter shaft SC, and further, in order to provide more transmission gear ranges, more gear shift clutches and more gears for constructing the transmission gear ranges may be provided.  
         [0035]    [0035]FIG. 2 shows details of the first clutch C 1  and the second clutch C 2 .  
         [0036]    In FIG. 2, the output shaft SE of the drive source  1  is connected to a flywheel  21 , and a clutch cover  22  is fixed onto the flywheel  21 . Further, a first pressure plate C 12  and a second pressure plate C 22  are rotationally fixed to the flywheel  21  and are freely movable in an axial direction. A clutch disc C 11  of the first clutch is arranged between the clutch cover  22  and the first pressure plate C 12 , and a clutch disc C 21  of the second clutch is arranged between the flywheel  21  and the second pressure plate C 22 . A first clutch spring C 13  urges the first pressure plate C 12  toward the clutch cover  22 , and a second clutch spring C 23  urges the second pressure plate C 22  away from the flywheel  21 . The first clutch disc C 11  is rotationally fixed to the first input shaft S 1  while being movable in the axial direction, and the second clutch disc C 22  is rotationally fixed to the second input shaft S 2  while being movable in the axial direction.  
         [0037]    The first pressure plate C 12  is connected to a first release bearing C 15  via a first clutch first operating link C 14 A, a first clutch second operating link C 14 B and a first clutch third operating link C 14 C. An operating force of the clutch is output by a hydraulic cylinder mechanism including a first release cylinder C 17 B and a first release piston C 17 A, and a pressure within the cylinder is adjusted from an external portion via a first hydraulic pipe C 18 . In this case, since the first clutch first operating link C 14 A, the first clutch second operating link C 14 B and the first clutch third operating link C 14 C for operating the first pressure plate C 12  are mounted to the clutch cover  22  so that they rotate together with the flywheel  21 , and the hydraulic cylinder mechanism for generating the operating force is mounted to a transmission body not rotatable, the first release bearing C 15  is arranged between the first clutch third operating link C 14 C and the first release bearing holder C 16  to absorb a relative rotational therebetween.  
         [0038]    When a high pressure is supplied to the hydraulic cylinder mechanism of the first clutch C 1  from an external portion, the first release piston is pressed out (moved in a left direction in the drawing), so as to press the first release bearing holder C 16 , the first release bearing C 15  and the first clutch third operating link C 14 C. Since the first clutch third operating link C 14 C is connected to the first clutch second operating link C 14 B rotatably around a pivot C 19 , the first clutch second operating link C 14 B draws the first clutch first operating link C 14 A (moves in a right direction in the drawing). When the first clutch first operating link C 14 A is drawn by the first clutch second operating link C 14 B, the first pressure plate C 12  releases a pressing of the first clutch disc C 11 , and the first clutch is disengaged. Further, when the pressure is not applied to the hydraulic cylinder mechanism of the first clutch from the external portion, a force of the first clutch spring C 13  presses the first clutch disc C 11  against the clutch cover  22  through the first pressure plate C 12  presses, whereby the first clutch is engaged.  
         [0039]    The second pressure plate C 22  is connected to a second release bearing C 25  via a second clutch first operating link C 24 A and a second clutch second operating link C 24 B. An operating force of the clutch is output by a hydraulic cylinder mechanism including a second release cylinder C 27 B and a second release piston C 27 A, and a pressure within the cylinder is adjusted from an external portion via a second hydraulic pipe C 28 . In this case, since the second clutch first operating link C 24 A and the second clutch second operating link C 24 B for operating the second pressure plate C 22  are mounted to the clutch cover  22 , they rotate together with the flywheel  21 . Since the hydraulic cylinder mechanism for generating the operating force is mounted to the transmission body, it does not rotate, and the second release bearing C 25  is arranged between the second clutch second operating link C 24 B and the second release bearing holder C 26  to absorb a relative rotational motion therebetween. In the case that a high pressure is supplied to the hydraulic cylinder mechanism of the second clutch from the external portion, the second release piston is projected out (moved in a left direction in the drawing), so as to press the second release bearing holder C 26 , the second release bearing C 25  and the second clutch second operating link C 24 B. The second clutch second operating link C 24 B is connected to the second clutch first operating link C 24 A, and the second clutch first operating link C 24 A is also pressed (moved in a left direction in the drawing).  
         [0040]    When the second clutch first operating link C 24 A is pressed, the second pressure plate C 22  presses the second clutch disc C 21  toward the flywheel  21 , and the second clutch is engaged. Further, when the pressure is not applied to the hydraulic cylinder mechanism of the second clutch supplied from the external portion, the second pressure plate C 22  moves apart from the flywheel  21  due to a force of the second clutch spring C 23 , and cancels the pressing state of the second clutch disc C 21 , whereby the second clutch is disengaged.  
         [0041]    In an operation of a shift up, for example, the first shift stage is changed to the second shift stage. At the first shift stage, the first sleeve  31  of the first gear shift clutch SC 1  is positioned on a first shift stage driven gear and is engaged with the spline H 1  of the first shift stage driven gear. The first clutch C 1  is in an engaging state and the second clutch C 2  is in a disengaged state.  
         [0042]    [0042]FIG. 3 shows a flow chart at a time of shifting up.  
         [0043]    In FIG. 3, when a shift operation is started, the second clutch is set in a half clutch state transmitting a torque with slipping or relative rotation between the clutch disc C 21  and the flywheel  21 , and the first clutch is disengaged while increasing a transmission torque of the second clutch. It is preferable that a disengaging timing of the first clutch is a timing point where a torque transmitted by the second clutch reaches a torque transmitted by the first clutch and the second clutch before the first clutch is disengaged (that is, all or main part of the torque transmitted between the input and output shafts is transmitted by the second clutch although both the first and second clutches are in engaging state) so that the torque applied to the output shaft SO is changed from the torque transmitted by the first clutch C 1  to the torque transmitted by the second clutch C 2  without a considerable difference therebetween. Immediately after disengaging the first clutch, the first sleeve  31  of the first gear shift clutch SC 1  is moved to engage with the spline H 2  of the second speed driven gear from the spline H 1  of the first speed driven gear. The gradually increasing torque transmitted by the second clutch is adjusted to prevent the transmission torque of the second clutch from becoming excessively large while decreasing a rotational speed of the output shaft SE of the drive source  1  until a difference between a rotational speed VENG of the output shaft SE of the drive source  1  and a target rotational speed VENG_R of the output shaft SE of the drive source  1  is within a predetermined small range, wherein the target rotational speed VENG_R is a rotational speed obtainable if the output shaft SE is connected to the transmission output shaft SO through the first clutch C 1 , the counter shaft SC, the second speed drive gear D 2 , the second speed driven gear G 2 , the spline H 2 , the sleeve  31  and the hub  41 , that is, until a difference between a rotational speed of the sleeve  31  and the hub  41  driven by the second clutch C 2  (the rotational speed of the sleeve  31 , hub  41  or output shaft SO can be measured by a sensor) and a rotational speed of the spline H 2  obtainable if the output shaft SE is connected to the spline H 2  through the first clutch C 1 , the counter shaft SC, the second speed drive gear D 2  and the second speed driven gear G 2  (the rotational speed of the spline H 2  at this stage can be calculated from the measured rotational speed of the output shaft SE under an imaginary condition of that the output shaft SE is connected to the spline H 2  through the imaginarily engaged first clutch C 1 , the counter shaft SC, the second speed drive gear D 2  and the second speed driven gear G 2 ) is within a predetermined small range. Further, a rotational speed alignment judging value VSYNC is set on the basis of the traveling state. Here, under this state, the second clutch keeps the half clutch state yet.  
         [0044]    When a difference between the rotational speed VENG of the output shaft SE of the drive source  1  and the rotational speed VENG_R of the output shaft SE of the drive source  1  at the second stage calculated from the rotational speed of the transmission output shaft becomes equal to or less than the rotational number alignment judging value VSYNC, that is, the difference between the rotational speed of the sleeve  31  and the hub  41  and the rotational speed of the spline H 2  obtainable if the output shaft SE is connected to the spline H 2  through the first clutch C 1 , the counter shaft SC, the second speed drive gear D 2  and the second speed driven gear G 2  is within the predetermined small range (in this condition, the first sleeve  31  of the first gear shift clutch SC 1  becomes into engaging with the spline H 2  of the second speed driven gear) and the first sleeve  31  of the first gear shift clutch SC 1  reaches an engaging position with the spline H 2  of the second speed driven gear (in this condition, the rotational speed of the first input shaft Si is determined by the output shaft SO driven by the second clutch C 2 ), that is, when a difference between the rotational speed of the output shaft SE and a rotational speed of the first input shaft S 1  obtained after the sleeve  31  engages with the spline H 2  while engaging with the hub  41  is made within a predetermined range by adjusting the transmitted torque through the second clutch C 2 , the second clutch is disengaged and the first clutch is engaged, whereby the shift operation is finished.  
         [0045]    [0045]FIG. 4 shows the torques transmitted by the first and second clutches to the transmission output shaft SO. FIG. 5 shows variations of drive source output shaft rotational speeds VEG and VENG_R and transmission output shaft rotational speed, and FIG. 6 shows a transmission output shaft torque variation on a shift operation in accordance with the present invention.  
         [0046]    As is apparent from FIGS. 4, 5 and  6 , it is possible to make a mechanism for preventing the torque of the transmission output shaft from being reduced during the shift operation compact and light in weight, it is possible to prevent the torque from being reduced during the shift operation, the torque fluctuations during the shift operation can be suitably controlled by the transmission torque of the second clutch, and it is possible to put a mechanism having an improved controllability into practice. Further, it is possible to provide an automatic transmission which can reduce a shift shock felt by the occupant due to the torque fluctuations during the shift operation by controlling the torque during the shift operation and put a high quality shift operation into practice.  
         [0047]    The output of the drive source  1  during the shift operation may be adjusted, for example, by a throttle operation, a delaying operation of an ignition timing or the like the like which are not employed in the present embodiment. Further, for example, when the first shift stage is being changed to the second shift stage, the transmission torque of the second clutch is being adjusted so as to be prevented from becoming too large while increasing the transmission torque of the second clutch to reduce the rotational speed of the output shaft SE of the drive source  1 , and the first sleeve  31  of the first gear shift clutch SC 1  is in a neutral state in which the first sleeve  31  is engaged neither with the gear for the first shift stage nor with the gear for the second shift stage, a double clutch operation temporarily engaging the first clutch and again disengaging the first clutch may be performed so as to reduce the rotational speed of the first input shaft and the counter shaft, thereby assisting the engaging operation of the first sleeve  31  of the first gear shift clutch with the spline H 2  of the second speed driven gear.  
         [0048]    [0048]FIG. 7 is a view schematically showing an embodiment of a five-shift-stages transmission as an example of the invention.  
         [0049]    In FIG. 7, the second input shaft S 2  is connected to the second clutch C 2  through a one-way clutch OWC which transmits the torque through the second clutch C 2  and the one-way clutch OWC from the second clutch C 2  to the second input shaft S 2  when the rotational speed of the output shaft SO or the second input shaft S 2  is lower than that of the output shaft SE of the drive source  1  as the claimed input shaft and prevents the torque from being transmitted through the second clutch C 2  and the one-way clutch OWC when the rotational speed of the output shaft SO or the second input shaft S 2  is higher than that of the output shaft SE of the drive source  1  as the claimed input shaft.  
         [0050]    The counter shaft SC is rotated by a torque transmitted from the first input shaft S 1  through a counter drive gear DC to a counter driven gear GC. Further, a first speed drive gear D 1  and a first speed driven gear G 1  are used for the first shift stage, a second speed drive gear D 2  and a second speed driven gear G 2  are used for a second shift stage, a third speed drive gear D 3  and a third speed driven gear G 3  are used for a third shift stage and a fifth speed drive gear D 5  and a fifth speed driven gear G 5  are used for a fifth shift stage (for making the rotational speed of the output shaft So larger than that of the output shaft SE), between the counter shaft SC and the transmission output shaft SO. When the sleeves  31  and  32  are at respective neutral positions wherein the sleeves  31  and  32  are not in an engaging state with the splines H 1 , H 2 , H 3  and H 5  of the driven gears, so that the driven gears are freely rotatable with respect to the transmission output shaft. When moving the sleeve in the axial direction, one of the splines H 1 , H 2 , H 3  and H 5  of the driven gears engages with the spline on the sleeve  31  or  32  while the sleeve engages with the hub  41  or  42 , so that one of the driven gears or the first input shaft is fixed rotationally to the transmission output shaft.  
         [0051]    In the fifth shift stage, the spline H 5  for the fifth shift stage engages with the sleeve  32 , so that the first input shaft S 1  and the transmission output shaft SO are connected to each other through the fifth speed drive gear D 5  and the fifth speed driven gear G 5  for making the rotational speed of the output shaft SO larger than that of the output shaft SE. Since the second clutch transmits variably the torque from the output shaft SE to the transmission output shaft SO with slipping in the second clutch, the rotational speed of the output shaft SO is made smaller than that of the output shaft SE when the second clutch transmits the torque from the output shaft SE to the transmission output shaft SO. When the fifth speed driven gear G 5  is engaged with the sleeve  32  to be rotationally fixed to the output shaft SO through the hub  42  so that the rotational speed of the output shaft SO is made higher than that of the output shaft SE, the torque is prevented by the one-way clutch OWC from being transmitted from the output shaft SE to the output shaft SO so that the output shaft SO is driven only by the torque transmitted by the first clutch C 1 . Therefore, the change to the fifth shift stage from the fourth shift stage can be smooth, although the second clutch C 2  cannot harmonize rotations of the sleeve  32  or hub  42  and the spline H 5  and/or rotations of the output shaft SE and the first input shaft S 1  as the change to the second shift stage from the first shift stage in the first embodiment.  
         [0052]    [0052]FIG. 8 is a view schematically showing another embodiment of a four-shift-stages transmission as an example of the invention.  
         [0053]    In FIG. 8, the second input shaft S 2  has a hollow shape, the first input shaft S 1  is arranged at a radial inside of the second input shaft S 2  or surrounded by the second input shaft S 2 . The first input shaft S 1  is connected to the output shaft through the counter shaft SC, selected one of the pair of gears G 1  and D 1 , the pair of gears G 2  and D 2 , the pair of gears G 3  and D 3  and the pair of gears G 4  and D 4 , the sleeve  31  or  32 , and the hub  41  or  42 , and the second input shaft S 2  is connected to the output shaft SO through a pair of gears DC and GC mating with each other, an intermediate shaft SI, and a pair of gears DF and GF mating with each other, while the gears G 1  and G 2  are rotatable on the intermediate shaft SI, the gears D 3  and D 4  are rotatable on the counter shaft SC, the gears D 1  and D 2  are fixed to the counter shaft SC, the gears G 3  and G 4  are fixed to the intermediate shaft SI, the hub  41  is fixed to the intermediate shaft SI, and the hub  42  is fixed to the counter shaft SC.  
         [0054]    [0054]FIG. 9 is a view schematically showing another embodiment of a four-shift-stages transmission as an example of the invention.  
         [0055]    In FIG. 9, the first input shaft S 1  is connected to the output shaft through the counter shaft SC, selected one of the pair of gears G 1  and D 1 , the pair of gears G 2  and D 2 , the pair of gears G 3  and D 3  and the pair of gears G 4  and D 4 , the sleeve  31  or  32 , and the hub  41  or  42 , and the second input shaft S 2  is connected to the output shaft SO through the pair of gears DC and GC mating with each other, while the gears G 1  and G 2  are rotatable on the output shaft SO, the gears D 3  and D 4  are rotatable on the counter shaft SC, the gears D 1  and D 2  are fixed to the counter shaft SC, the gears G 3  and G 4  are fixed to the output shaft SO, the hub  41  is fixed to the output shaft SO, and the hub  42  is fixed to the counter shaft SC.  
         [0056]    [0056]FIG. 10 is a view schematically showing another embodiment of a four-shift-stages transmission as an example of the invention.  
         [0057]    In FIG. 10, the first input shaft S 1  is connected to the output shaft through the counter shaft SC, selected one of the pair of gears G 1  and D 1 , the pair of gears G 2  and D 2 , the pair of gears G 3  and D 3  and the pair of gears G 4  and D 4 , the sleeve  31  or  32 , and the hub  41  or  42 , and the second input shaft S 2  is connected to the output shaft SO through the pair of gears DC and GC, the intermediate shaft SI, and the pair of gears DF and GF, while the gears G 1  and G 2  are rotatable on the intermediate shaft SI, the gears D 3  and D 4  are rotatable on the counter shaft SC, the gears D 1  and D 2  are fixed to the counter shaft SC, the gears G 3  and G 4  are fixed to the intermediate shaft SI, the hub  41  is fixed to the intermediate shaft SI, and the hub  42  is fixed to the counter shaft SC.