Abstract:
A parallel shaft transmission comprising: an input shaft  1 , first counter shaft  2 , second counter shaft  3 , output shaft  4  that are parallel to each other; set of two first change gear trains  21   a   , 22   a   , 21   b   , 22   b  disposed between the input shaft  1  and first conter shaft  2 ; first and second clutch means  11, 12  for connecting and disconnecting the input shaft  1  and first change drive gear; set of two second change gear trains  22   a   , 23   a   , 22   c   , 23   c  disposed between the first counter shaft  2  and second counter shaft  3 ; third and fourth clutch means for connecting ad disconnecting the second counter shaft  3  and second change driven gear; third change gear trains  23   d   , 24   d  disposed between the second counter shaft  3  and output shaft  4 ; and fifth clutch means  15  for connecting and disconnecting the first counter shaft  2  and output shaft  4.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a parallel shaft transmission wherein a plurality of gear trains are disposed between shafts established parallel to each other, and each gear train has a plurality of clutching means for selecting the gear train to effect power transmission. 
     BACKGROUND OF THE INVENTION 
     Parallel shaft transmissions with such a constitution have had many uses such as in automobile transmissions. For example, parallel shaft automatic transmissions are disclosed in Japanese Patent Laid-open No. 57-103955(A) and Japanese Patent Laid-open No. 4-331852(A). 
     However, these parallel shaft transmissions have constitutions wherein a plurality of gear trains for engaging with each other are disposed parallel to the shafts and between the parallel shafts, and the gear train for effecting power transmission is selected by the connection and disconnection of a plurality of clutches disposed adjacent to the gears constituting each gear train. Therefore, the tendency is for the axial dimension of the transmission to increase; this tendency increases as the number of speeds increases. Particularly in automobile transmissions, the number of hydraulic clutches corresponds to the number of speeds, but hydraulic clutches structurally have relatively large axial and radial dimensions, and it is easy for the transmission to become large. 
     Also, in recent years, automobile transmissions have tended to have a greater number of speeds because of the demands for drivability and improvements in fuel consumption. Three speed transmissions changed to four speed transmissions; once five speed transmissions came into use, six speed transmissions were requested because of further demands for drivability and improvements in fuel consumption. This is consequently a situation where it is easy for transmissions to become larger and larger. Likewise, as the transmissions came to have larger numbers of speeds, the number of clutches increased and the increased size and weight of transmissions and consequent increases in manufacturing costs have become problematic. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a parallel shaft transmission having a constitution wherein the disposition of the gears and clutches is contrived so that the transmission can have an increased number of speeds and be as compact as possible. 
     The parallel shaft transmission relating to the present invention has the following constitution: an input shaft, first counter shaft, second counter shaft, and output shaft established on the same axis as the first counter shaft and able to rotate relatively thereto, with each established parallel to the others; set of two first change gear trains comprising first and second change drive gears (for example, first gear  21   a  and second gear  21   b  in FIG. 1 of the embodiment) established on the input shaft, and first and second change driven gears (for example, third gear  22   a  and fourth gear  22   b  in FIG. 1 of the embodiment), established on the first counter shaft, for engaging with first and second change drive gears; first and second clutch means (for example, first clutch  11  and second clutch  12  in FIG. 1 of the embodiment), established on the input shaft, for connecting and disconnecting the input shaft and the set of two first change drive gears; set of two second change gear trains comprising third and fourth change drive gears (for example, third gear  22   a  and fifth gear  22   c  in FIG. 1 of the embodiment) established on the first counter shaft, and third and fourth change driven gears (for example, sixth gear  23   a  and seventh gear  23   c  in FIG. 1 of the embodiment), established on the second counter shaft, for engaging with the third and fourth change drive gears; third and fourth clutch means (for example, the third clutch  13  and fourth clutch  14  in FIG. 1 of the embodiment), established on the second counter shaft, for connecting and disconnecting the second counter shaft and the set of two second change driven gears; third change gear train comprising a fifth change drive gear (for example, the eighth gear  23   d  in FIG. 1 of the embodiment) established on the second counter shaft, and fifth change driven gear (for example, the ninth gear  24   d  in FIG. 1 of the embodiment), established on the output shaft, for engaging with the fifth change drive gear; and fifth clutch means (for example, fifth clutch  15  in FIG. 1 of the embodiment), established between the first counter shaft and output shaft, for connecting and disconnecting the first counter shaft and output shaft. 
     In a parallel shaft transmission with such a constitution, the driving force transmitted from the engine to the input shaft is transmitted to the output shaft at a reduction ratio corresponding to the selected gear train, by means of a gear train such as the first change gear train, second change gear train, and third change gear train, through the selective connection and disconnection of each clutch means established on the input shaft and second counter shaft. Furthermore, by the connection and disconnection of the fifth clutch means established between the first counter shaft and output shaft, the driving force of the input shaft can be transmitted to the output shaft at the reduction ratio of the first gear train, without passing through the second gear train and third gear train. For this reason, a transmission with the same number of speeds can be constituted with a number of clutches less than the number of speeds, such as a six forward speed transmission constituted with five hydraulic clutches. Consequently, a parallel shaft transmission, with improved drivability and fuel consumption and with an increased number of speeds, can be provided without cost increases or increased size and weight of the transmission due to an increased number of clutches. 
     Moreover, a parallel shaft transmission can be constituted as follows: a reverse coupling gear train (for example, reverse gear trains  21   r ,  26 ,  22   r  in FIG. 1 of the embodiment) is established between the input shaft and first counter shaft; and a forward and reverse switching mechanism (for example, reverse selector  16  in FIG. 1 of the embodiment) is disposed on the input shaft. With this constitution, the clutch means (for example, second clutch  12  and third clutch  13  in FIG. 1 of the embodiment) disposed on the first counter shaft or second counter shaft can be used both for forward and reverse. For this reason, a transmission, with which forward and reverse are possible, can be constituted without increasing the number of clutch means and the size of the transmission, and a compact parallel shaft transmission can be provided. 
     Also, a parallel shaft transmission can be constituted as follows: a reverse coupling gear train is established between the input shaft and first counter shaft; and a forward and reverse switching mechanism (for example, the reverse clutch  46  in FIG. 9 of the embodiment and the reverse selector  86  in FIG. 10 of the embodiment) is disposed on the first counter shaft. With this constitution, the clutch means disposed on the first counter shaft or second counter shaft as above can be used both for forward and reverse, and a transmission, with which forward and reverse are possible, can be constituted without increases to transmission size. Furthermore, because the forward and reverse switching mechanism is disposed on an axis with few clutch means, increases to the axial dimensions can be minimized and a compact parallel shaft transmission can be provided. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: 
     FIG. 1 is a skeleton view showing the power transmission constitution of a parallel shaft transmission relating to a first embodiment of the present invention; 
     FIG. 2 is a skeleton view showing the power transmission path in LOW gear of a parallel shaft transmission relating to a first embodiment of the present invention; 
     FIG. 3 is a skeleton view showing the power transmission path in second gear of a parallel shaft transmission relating to a first embodiment of the present invention; 
     FIG. 4 is a skeleton view showing the power transmission path in third gear of a parallel shaft transmission relating to a first embodiment of the present invention; 
     FIG. 5 is a skeleton view showing the power transmission path in fourth gear of a parallel shaft transmission relating to a first embodiment of the present invention; 
     FIG. 6 is a skeleton view showing the power transmission path in fifth gear of a parallel shaft transmission relating to a first embodiment of the present invention; 
     FIG. 7 is a skeleton view showing the power transmission path in sixth gear of a parallel shaft transmission relating to a first embodiment of the present invention; 
     FIG. 8 is a skeleton view showing the power transmission path in reverse gear (reverse gear) of a parallel shaft transmission relating to a first embodiment of the present invention; 
     FIG. 9 is a skeleton view showing the power transmission constitution of a parallel shaft transmission relating to a second embodiment of the present invention; and 
     FIG. 10 is a skeleton view showing the power transmission constitution of a parallel shaft transmission relating to a third embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a first embodiment of the parallel shaft transmission relating to the present invention. In this parallel shaft transmission, driving force is transmitted from an engine output shaft of a vehicle, not shown, via a torque converter to the input shaft  1 . After being converted at the desired gear ratio by the transmission mechanism TM of the parallel shaft transmission, the driving force is transferred to the right and left drive wheels of the vehicle via a differential mechanism connected to the output shaft  4  of this transmission mechanism TM. 
     The parallel shaft transmission mechanism TM comprises an input shaft  1 , a first counter shaft  2 , a second counter shaft  3 , and an output shaft  4  that are parallel to each other. Among those, the first counter shaft  2  and output shaft  4  are disposed on the same axis and are constituted so as to rotate relatively to each other. 
     The input shaft  1  is supported rotatably by bearings, not shown, while the left end thereof in the FIG. is connected to the turbine of the torque converter; the input shaft receives driving force transmitted by the torque converter from the engine and rotates with the turbine of the converter. The first gear  21   a , first clutch  11 , second clutch  12 , second gear  21   b , reverse selector  16 , and reverse drive gear  21   r  are disposed on the input shaft  1  in that order from the left side of the figure (torque converter side). The first gear  21   a  is disposed rotatably on the shaft of the input shaft  1  and is connected to and disconnected from the input shaft  1  by the hydraulically actuated first clutch  11 . The second gear  21   b  and reverse drive gear  21   r  are disposed rotatably on the input shaft  1 . Either gear is selected by the reverse selector  16  (for example, dog tooth clutch or servo-synchro mechanism) for switching between forward and reverse, while the selected gear is connected to and disconnected from the first shaft by the action of the second clutch  12 . 
     The first counter shaft  2  is disposed coaxially to and so as to cover the outside of the output shaft  4  and is constituted so as to rotate relatively thereto due to a bearing, not shown, disposed between the output shaft  2  and the first counter shaft. The fifth clutch  15 , third gear  22   a , fourth gear  22   b , fifth gear  22   c , and reverse driven gear  22   r  are disposed on the shaft of the first counter shaft  2  in that order from the left side of the figure Each gear is joined with the second counter shaft  2  and rotates as one therewith. The fifth clutch  15  is hydraulically powered to connect and disconnect the second counter shaft  2  and output shaft  4  which rotate together. 
     The second counter shaft  2  is supported rotatably by bearings, not shown. The eighth gear  23   d , sixth gear  23   a , fourth clutch  14 , third clutch  13 , and seventh gear  23   c  are disposed on the axis thereof in order from the left side of the figure The sixth gear  23   a  and seventh gear  23   c  are disposed rotatably relative to the second counter shaft  3  and are each connected to and disconnected from the second counter shaft  3  by the hydraulically actuated fourth clutch  14  and third clutch  13 . The eighth gear  23   d  is joined with the second counter shaft  3 . 
     The output shaft  4  is supported rotatably with respect to the case of the transmission by bearings, not shown, while being disposed so as to rotate relatively to the first counter shaft  2  due to bearings, not shown, between the output shaft and the first counter shaft  2  disposed coaxially about the outside of this output shaft  4 . A ninth gear  24   d  and fifth clutch  15  are disposed in that order from the left side of the figure on the axis of the output shaft; the ninth gear  24   d  is joined to the output shaft  4 . The fifth clutch  15  connects and disconnects the output shaft  4  and first counter shaft  2  with hydraulic power. 
     Moreover, as shown, the first gear  21   a  engages with the third gear  22   a  and, the third gear  22   a  engages with the sixth gear  23   a , the second gear  21   b  engages with the fourth gear  22   b , the fifth gear  22   c  engages with the seventh gear  23   c , and the eighth gear  23   d  engages with the ninth gear  23   d . Furthermore, the reverse drive gear  21   r  engages with the reverse driven gear  22   r  via the reverse idler gear  26 . 
     For a parallel shaft transmission with the abovementioned constitution, the setting of each gear and power transmission path thereof are explained with reference to FIGS. 2 through  8 . Moreover, in this transmission, LOW (first), second, third, fourth, fifth, and sixth gears are established in the forward range (D range) and a reverse gear is established in the reverse range (R range). This range switching is effected as follows: switching to forward range is accomplished by moving the reverse selector  16  to the left in the figure and engaging the second gear and input shaft  1 ; switching to the reverse range is accomplished by moving the reverse selector  16  to the right in the figure and engaging the reverse drive gear  21   r  and the input shaft  1 . 
     Each gear in the forward range is explained next. Low gear is established by engaging the first clutch  11  and the third clutch  13 ; the power transmission path in this case is shown with the bold lines in FIG.  2 . Transmitted from the engine via the torque converter to the input shaft  1 , the rotary driving force is transmitted to the first gear  21   a  by the engagement of the first clutch  11  and rotates the first gear  21   a  with the input shaft; the third gear  22   a  engaged with the first gear  21   a  is caused to rotate; and the first counter shaft  2  is driven. Because each gear on the first counter shaft (third gear  22   a , fourth gear  22   b , fifth gear  22   c ) is joined to the first counter shaft  2 , the seventh gear  23   c  engaged with the fifth gear  22   c  is therefore rotated and the rotary driving force is transmitted to the second counter shaft  3  due to the engagement of the third clutch  13 . The eighth gear  23   d  is joined to the second counter shaft  3 , the rotary driving force transmitted to this gear drives the ninth gear  23   d  engaged with the eighth gear  23   d , and the rotary driving force is transmitted to the output shaft  4 . 
     Second gear is established by engaging the second clutch  12  and the third clutch  13 ; the power transmission path in this case is shown with the bold line in FIG.  3 . In forward gear, because the reverse selector  16  is moved to the left and the second gear  21   b  and second clutch  12  are engaged. Therefore, the rotary driving force transmitted from the engine via the torque converter to the input shaft  1  is transmitted to the second gear due to the engagement of the second clutch  12  and rotates the first counter shaft  2  via the fourth gear  22   b  engaged therewith. The subsequent transmission paths are the same as in first gear; the rotary driving force transmitted to the first counter shaft  2  is transmitted to the second counter shaft  3  by the engagement of the third clutch  13  via the fifth gear  22   c  attached to the shaft and the seventh gear  23   c  engaged therewith; the rotary driving force is transmitted to the output shaft  4  via the eighth gear  23   d  on that shaft and the ninth gear  24   d  engaged therewith. 
     Third gear is established by engaging the first clutch  11  and the fourth clutch  14 ; the power transmission path in this case is shown with the bold line in FIG.  4 . Transmitted from the engine via the torque converter to the input shaft  1 , the rotary driving force is transmitted to the first gear  21   a  by the engagement of the first clutch  11 , rotates the third gear  22   a  engaged with the first gear  21   a , and is transmitted to the first counter shaft  2 . The third gear  22   a  engages with the sixth gear  23   a  on the second counter shaft as well; the rotary driving force is transmitted to the second counter shaft  3  by the engagement of the fourth clutch  14 . The driving force goes through the eighth gear  23   d  joined with the second counter shaft, the ninth gear  24   d , engaged with this gear, is driven, and the rotary driving force is transmitted to the output shaft  4 . 
     Fourth gear is established by engaging the second clutch  12  and fourth clutch  14 ; the power transmission path in this case is shown with the bold line in FIG.  5 . Transmitted from the engine via the torque converter to the input shaft  1 , the rotary driving force is transmitted to the second gear  21   b  by the engagement of the second clutch  12  and is transmitted to the first counter shaft  2  by rotating the fourth gear  22   b , engaged therewith. Because each gear on the first counter shaft is joined therewith, the third gear  22   a  on this shaft is rotated and the sixth gear  23   a  engaged therewith is rotated. With the engagement of the fourth clutch  14 , the rotary driving force is transmitted to the second counter shaft  3 . The driving force goes through the eighth gear  23   d  joined with the second counter shaft, the ninth gear  24   d , engaged with this gear, is driven, and the rotary driving force is transmitted to the output shaft  4 . 
     Fifth gear is established by engaging the first clutch  11  and fifth clutch  15 ; the power transmission path in this case is shown with the bold line in FIG.  6 . Transmitted from the engine via the torque converter to the input shaft  1 , the rotary driving force is transmitted to the first gear  21   a  by the engagement of the first clutch  11  and is transmitted to the first counter shaft  2  by rotating the third gear  22   a  engaged therewith. Then the fifth clutch  15  causes the engagement of the first counter shaft  2  and output shaft  4 , and the output shaft  4  is rotated at the same frequency as the first counter shaft  2 . 
     Sixth gear is established by engaging the second clutch  12  and fifth clutch  15 ; the power transmission path in this case is shown with the bold line in FIG.  7 . Transmitted from the engine via the torque converter to the input shaft  1 , the rotary driving force is transmitted to the second gear  21   b  by the engagement of the second clutch  12  and is transmitted to the first counter shaft  2  by rotating the fourth gear  22   b  engaged therewith. The fifth clutch  15  effects the engagement of the first counter shaft  2  and output shaft  4 ; the output shaft  4  is rotated at the same frequency as the first counter shaft  2 . 
     Next, reverse gear is explained. Reverse gear is established by moving the reverse selector  16  to the right and engaging the second clutch  12  and the reverse drive gear  21   r , while engaging the second clutch  12  and third clutch  13 . The power transmission path for this case is shown with the bold line in FIG.  8 . Transmitted from the engine via the torque converter to the input shaft  1 , the rotary driving force is transmitted to the reverse drive gear  21   r  by the engagement of the second clutch  12 , rotates the reverse driven gear  22   r  via the reverse idler gear engaged with both, and causes the first counter shaft  2  to rotate in the opposite direction from the forward speeds. The rotary driving force transmitted to the, first counter shaft  2  is transmitted to the second counter shaft  3  by the engagement of the third clutch  13  via the fifth gear  22   c  attached to the shaft and the seventh gear  23   c  engaged therewith; the rotary driving force, with a direction opposite to the forward speeds, is transmitted to the output shaft  4  via the eighth gear  23   d  on that shaft and the ninth gear  24   d  engaged therewith. As understood from this, the second clutch and third clutch also operate as reverse gear clutches. 
     In a parallel shaft transmission with the abovementioned constitution, the rotary driving force transmitted from the engine via a torque converter constitutes four forward gears via the second counter shaft  3  by the selective connection and disconnection of the first clutch  11 , second clutch  12 , third clutch  13 , and fourth clutch  14  established on the output shaft  1  sic and second counter shaft, constitutes two forward gears, without passing through the second counter shaft, by the connection and disconnection of the fifth clutch  15  established between the first counter shaft  1  and output shaft  4 , and constitutes a parallel shaft transmission with six forward gears with a total of five hydraulic clutches. For this reason, a transmission with a greater number of gears can be constituted with a smaller number of clutches, and consequently a compact transmission can be provided, as compared to a conventional transmission having a hydraulic clutch for each gear. 
     Furthermore, with the parallel shaft transmission in the abovementioned embodiment, the second clutch  12  and third clutch  13  double for forward and reverse speeds. A total of seven speeds, including the six forward gears and reverse (furthermore, it is also possible to have a total of nine gears, with three reverse gears through the engagement of the second clutch  12 , fourth clutch  14 , and fifth clutch  15 ) are accomplished with five hydraulic clutches. For this reason, a transmission with many gears including reverse can be constituted with a small number of clutches and a more compact transmission can be provided without increasing the number of hydraulic clutches. 
     Moreover, the abovementioned embodiment shows an example where the seventh gear  23   c  is disposed rotatably with respect to the second counter shaft  3  and is engaged with the second counter shaft  3  by the third clutch  13  in LOW gear and second gear (and in reverse). However, a one way clutch  17  can be disposed along with the third clutch between the seventh gear  23   c  and the second counter shaft  3  in the forward range (D range) and the clutch action of the one way clutch  17  can be utilized without being engaged with the third clutch. With this type of constitution, a smooth changing action can be attained with the one way clutch  17  in the forward range (D range), while the third clutch is engaged and strong driving force and engine braking are effected in low hold gear and second hold gear (or reverse gear). 
     Next a second embodiment of the parallel shaft transmission relating to the present invention is explained with reference to FIG.  9 . In this parallel shaft transmission, driving force is transmitted to an input shaft  31  via a torque converter from an engine output shaft of a vehicle, not shown, and converted at the desired gear ratio by the transmission mechanism TM′ of the parallel shaft transmission, then the driving force is transmitted to the drive wheels on either side of the vehicle via a differential, mechanism connected to the output shaft  34  of this transmission mechanism TM′. 
     The parallel shaft transmission mechanism TM′ comprises an input shaft  31 , first counter shaft  32 , second counter shaft  33 , and output shaft  34  that are mutually parallel; the first counter shaft  32  and output shaft  34  are established on the same axis and constituted so as to rotate relative to each other. 
     The input shaft  31  is supported rotatably by bearings  61   a ,  61   b , while the left end, in the figure of the input shaft  31  is connected to the turbine of the torque converter. The input shaft  31  receives the driving force transmitted from the engine to the torque converter and rotates with the turbine of the converter. The following are disposed on the input shaft  31  in order from the left side in the figure (the torque converter side): first gear  51   a , first clutch  41 , second gear  51   b , second clutch  42 , and reverse drive gear  51   r . The first gear  51   a  and second gear  51   b  are disposed rotatably on the axis of the input shaft  1  and are connected and disconnected from the input shaft  31  by the hydraulically actuated first clutch  41  and second clutch  42 . 
     The first counter shaft  32  is disposed on the same axis as and covers the outside of the output shaft  34  and is constituted so as to rotate relatively thereto with bearings, not shown, disposed between the output shaft and the counter shaft. The following are disposed on the shaft of the first counter shaft  32  in order from the left side of the figure: fifth clutch  43 , third gear  52   a , fourth gear  52   b , and fifth gear  52   c . Each gear on this shaft is joined to the second counter shaft  32  and rotates therewith. The fifth clutch  45  hydraulically connects and disconnects the second counter shaft  32  and output shaft  34  that rotate as one. 
     The second counter shaft  33  is supported rotatably by bearings  63   a ,  63   b ; the following are disposed on this shaft in order from the left side: sixth gear  53   a , fourth clutch  44 , seventh gear  53   c , third clutch  43 , and eighth gear  53   d . The sixth gear  53   a  and seventh gear  53   c  are disposed rotatably with respect to the second counter shaft  33  and are each connected and disconnected from the second counter shaft  33  by the hydraulically actuated fourth clutch  44  and third clutch  43 . The eighth gear  53   d  is connected to the second counter shaft  33 . 
     The output shaft  34  is supported rotatably by bearings  64   a  and  64   b , while being constituted so as to rotate relatively to the first counter shaft  32  disposed on the same axis as this output shaft  34 , due to bearings, not shown, therebetween. The following are disposed on the shaft of the output shaft  34  in order from the left side of the figure: fifth clutch  45 , ninth gear  54   d , reverse driven gear  54   r , and reverse clutch.  46 . The ninth gear  54   d  is joined to this output shaft, while the reverse driven gear  54   r  is disposed rotatably with respect to this output shaft and connected and disconnected from the output shaft by the hydraulically actuated reverse clutch  46 . The fifth clutch  45  hydraulically connects and disconnects the first counter shaft  32  and output shaft  34  disposed on the same axis. 
     As shown in the figure, the first gear  51   a  engages with the third gear  52   a , the third gear  52   a  engages with the sixth gear  53   a , the second gear  51   b  engages with the fourth gear  52   b , the fifth gear  52   c  engages with the seventh gear  5   c , and the eighth gear  53   d  engages with the ninth gear  54   d . Furthermore the reverse drive gear  51   r  engages with the reverse driven gear  52   r  via the reverse idler gear  56 . 
     In the parallel shaft transmission with the abovementioned type of constitution, the first clutch through the fifth clutch are selectively actuated in the same combinations as in the first embodiment discussed above in the state where engagement of the reverse clutch  46  is released and each gear, from LOW gear to sixth gear in the forward range (D range), is established thereby. Also, in the reverse range (R range), the engagements of the first clutch through the fifth clutch are released and rotary driving power, with a rotation opposite to that of forward gear, is transmitted to the output shaft by engagement of the reverse clutch  46 . 
     In the case of a transmission with such a constitution, a parallel shaft transmission with six forward gears is constituted with five hydraulic clutches, like the first embodiment discussed above. Consequently, a more compact transmission can be provided, as compared to a conventional transmission with a hydraulic clutch for each gear. Also, in the present embodiment, a reverse-only clutch is disposed on the output shaft. For this reason, a compact transmission can be provided because increases to the length of the input shaft, that easily becomes long when a plurality of hydraulic clutches are disposed thereon, are avoided. 
     Moreover, in the present embodiment like the first embodiment discussed above, a one way clutch  47  can be disposed between the seventh gear  53   c  and the second counter shaft  33  and the clutch action of the one way clutch  47  can be used without engaging the third clutch  43  in the forward range (D range). With this type of constitution, smooth changing action can be attained in the forward range,(D range), while the third clutch  43  is engaged and strong driving force and engine braking can be effected in LOW hold gear and second hold gear. 
     Next, the third embodiment relating to the present invention is explained using FIG.  10 . This embodiment is a transmission with approximately the same constitution as the first embodiment discussed above, only with a reverse selector  86  for switching between forward and reverse established on the first counter shaft  72 . 
     The parallel shaft transmission mechanism TM′ comprises an input shaft  71 , first counter shaft  72 , second counter shaft  73 , and output shaft  74  that are parallel to each other. Transmitted from the output shaft of the engine of a vehicle, not shown, via a torque converter to the input shaft  71 , the rotary driving force is converted at the desired reduction ratio by the transmission mechanism TM″; then the driving force is transmitted to the right and left drive wheels of the vehicle via a differential mechanism connected to the output shaft  74 . Moreover, the first counter shaft  72  and output shaft  74  are disposed on the same axis and constituted so as to rotate relatively to each other. 
     The input shaft  71  is supported rotatably by bearings, not shown, and is rotated by the driving force transmitted from the engine via the torque converter. The following are disposed on the input shaft  71  in order from the left side of the figure: first gear  91   a , first clutch  81 , second clutch  82 , second gear  91   b , and reverse drive gear  91   r . The first gear  91   a  is disposed rotatably on the shaft of the input shaft  1  and connected and disconnected to the input shaft  71  by the hydraulically actuated first clutch  81 . The second gear  91   b  and reverse drive gear  91   r  are joined together and disposed rotatably on the input shaft  71  and connected and disconnected from the input shaft  71  by the hydraulically actuated second clutch  82 . 
     The first counter shaft  72  is disposed on the same axis as and covering the outside of the output shaft  74  and is constituted so as to rotate relatively thereto due to bearings, not shown, disposed between the counter shaft and the output shaft  74 . The following are disposed on the first counter shaft  72  in order from the left side of the figure: fifth clutch  85 , third gear  92   a , fifth gear  92   c , fourth gear  92   b , reverse selector  86  for switching between forward and reverse, and the reverse driven gear  22   r . The third gear  92   a  and fifth gear  92   c  are joined to the second counter shaft  72  and rotate as one therewith. The fourth gear  92   b  and reverse driven gear  92   r  are disposed rotatably on the second counter shaft; the gear selected by the reverse selector (for example, dog toothed clutch or servo-synchro)  86  engages with the second counter shaft  72  and rotates and is driven by this shaft. Also, the fifth clutch  85  hydraulically connects and disconnects the second counter shaft  72  and output shaft  74 . 
     The second counter shaft  73  is supported rotatably by bearings, not shown; the following are disposed on the shaft from the left side of the figure: eighth gear  93   d , sixth gear  93   a , fourth clutch  84 , third clutch  83 , and seventh gear  93   c . The sixth gear  93   a  and seventh gear  93   c  are disposed rotatably with respect to the second counter shaft  73  and are each connected and disconnected from the second counter shaft  73  by the hydraulically actuated fourth clutch  84  and third clutch  83 . The eighth gear  93   d  is joined to the second counter shaft  73 . 
     The output shaft  74  is supported rotatably with respect to the case of the transmission by bearings, not shown, while being disposed rotatably relative to the first counter shaft  72  by bearings, not shown, between the output shaft and the first counter shaft  72  disposed on the same axis and outside of the output shaft  74 . The ninth gear  94   d  and fifth clutch  85  are disposed in that order from the left side of the drawing on the shaft of the output shaft  74 ; the ninth gear  94   d  is joined to the output shaft  74 . The fifth clutch  85  hydraulically connects and disconnects the output shaft  74  and first counter shaft  72 . 
     As shown in the drawing, the first gear  91   a  engages with the third gear  92   a , the third gear  92   a  engages with the sixth gear  93   a , the second gear  91   b  engages with the fourth gear  92   b , the fifth gear  92   c  engages with the seventh gear  93   c , and the eighth gear  93   d  engages with the ninth gear  94   d . Also, the reverse drive gear  91   r  engages with the reverse driven gear  92   r  via the reverse idler gear  96 . 
     In the parallel shaft transmission with the abovementioned type of constitution, the first clutch through the fifth clutch are selectively actuated in the same combinations as in the first embodiment discussed above in the state where the reverse selector  86  is moved to the left, and each gear, from LOW gear to sixth gear in the forward range (D range), is established thereby. Also, in the reverse range (R range), the reverse selector  86  is moved to the right, and the second clutch  82  and third clutch  83  are engaged, whereby rotary driving power, with a rotation opposite to that of forward gear, is transmitted to the output shaft  74 . 
     In the case of a transmission with such a constitution, a parallel shaft transmission with six forward gears is constituted with five hydraulic clutches, like the first embodiment discussed above. Consequently, a more compact transmission can be provided, as compared to a conventional transmission with a hydraulic clutch for each gear. Also, in the present embodiment, a reverse selector  86  is disposed on the first counter shaft. For this reason, a compact transmission can be provided because increases to the length of the input shaft, that easily becomes long, are avoided and because a total of seven gears, six forward gears and a reverse gear (a total of nine gears with three reverse gears is also possible) are constituted with five hydraulic clutches. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a depart from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 
     RELATED APPLICATIONS 
     This application claims the priority of Japanese Patent Application No.11-159120 filed on Jun. 7, 1999, which is incorporated herein by reference.