Abstract:
A transmission for a vehicle which can be applied to a shift mechanism where a shaft itself is rotated and having a simple configuration and axial miniaturization. A transmission for a vehicle in which a plurality of transmission shafts are provided each of which supports a plurality of transmission gears in a row and are arranged in parallel so that mutually corresponding transmission gears are engaged and transmission gears rotating in synchronization with the hollow shaft are selectively switched. Every transmission shaft is provided with a clutch mechanism provided between the hollow shaft and each transmission gear for fitting the hollow shaft and each transmission gear or releasing the fitting and a clutch actuator housed in the hollow shaft and the clutch mechanism selectively fits any transmission gear to the hollow shaft according to the axial position of the clutch actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present nonprovisional application claims priority under 35 USC 119 to Japanese Patent Application No. 2002-029553 filed on Feb. 6, 2002 the entire contents thereof is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a transmission for a vehicle, more particularly, to a constant-mesh type transmission for a vehicle in which plural transmission shafts each of which supports plural transmission gears in a row are arranged in parallel so that mutually corresponding transmission gears are engaged. 
   2. Description of Background Art 
   For a conventional type transmission for a bicycle, as disclosed in Japanese published unexamined patent application No. Hei9-249183, a planetary gear type transmission is provided with a hub spindle (a sun gear) fastened to a bicycle frame so that the hub spindle is not turned. A hub flange is attached to the periphery of the hub spindle so that the hub flange can be rotated. Plural gears (planetary gears) are provided between the hub spindle and the hub flange wherein pedal effort transmitted to a chain sprocket is varied at multiple stages by the plural planetary gears and each clutch mechanism and is transmitted to the hub flange is known. An actuator for fitting a ratchet one-way mechanism of the clutch mechanism or releasing the fitting is inserted into the hub spindle, and the fitting of the ratchet one-way mechanism and the release of the fitting are executed by revolving the actuator around the hub spindle by a predetermined angle. 
   The planetary gear type transmission is composed of multiple parts. Thus, the transmission efficiency is low and axial downsizing is particularly difficult because the multiple parts are axially arranged. Therefore, for a transmission for a bicycle the limit of the width is severe. Thus, the conventional type of transmission is not desirable. 
   In the prior art described above, as the actuator for fitting the ratchet one-way mechanism of the clutch mechanism or releasing the fitting is cylindrical and is required to be turned by a predetermined angle on the periphery of the spindle, it is difficult to apply the prior art to a transmission in which a spindle itself is rotated. Further, in the prior art, the actuator cannot be turned in a state in which torque is applied and the shift is disabled. 
   SUMMARY AND OBJECTS OF THE INVENTION 
   It is an object of the present invention to solve the problems of the prior art and to provide a transmission for a bicycle which can be applied to a shift mechanism in which a spindle itself is revolved, has a simple configuration and can be axially miniaturized. 
   To achieve this object, the present invention includes a transmission for a vehicle in which plural transmission shafts include hollow shafts wherein each hollow shaft supports plural transmission gears in a row that are arranged in parallel so that mutually corresponding transmission gears are engaged and a desired speed reducing ratio is acquired by selectively switching the transmission gear revolving in synchronization with the hollow shaft every transmission shaft. 
   (1) A clutch mechanism is provided between the hollow shaft and the transmission gear for synchronizing the hollow shaft and each transmission gear or releasing the synchronization. A clutch actuator is housed in the hollow shaft that is provided. The clutch mechanism selectively synchronizes each transmission gear with the hollow shaft or releases the synchronization according to an axial position of the clutch actuator. 
   (2) The clutch mechanism is provided with a pin member housed in an opening radially piercing the side wall of the hollow shaft so that the pin member can move vertically and a fitting member for fitting each transmission gear to the hollow shaft or releasing the fitting in interlock with the vertical motion of the pin member. The clutch actuator is in the shape of a rod and is provided with an irregular cam part arranged on its outside face according to a predetermined rule. The pin member is selectively made to vertically move by moving the clutch actuator in the hollow shaft and fitting the cam part to the bottom of the pin member. 
   (3) The cam part is circumferentially provided with an inclined face continuing from a cam groove to a cam crest. 
   According to the characteristic (1), as the clutch actuator can be housed in the hollow shaft, the constant-mesh type transmission which has a simple configuration and in which axial miniaturization is enabled can also be realized in a drive line in which a shaft itself is revolved. 
   According to the characteristic (2), the clutch mechanism can be realized by a simple configuration in the constant-mesh type transmission in which the clutch actuator is housed in the shaft. 
   According to the characteristic (3), as the pin member can be lifted from the cam groove to the cam crest by small force and smoothly, shift is enabled even if pedal effort is applied. 
   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 hereinbelow 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 side view showing a bicycle provided with a transmission equivalent to one embodiment of the present invention; 
       FIG. 2  is a sectional view viewed along a line I—I showing the pedal effort transmission shown in  FIG. 1 ; 
     FIGS.  3 ( a )- 3 ( c ) show the configuration of a shift plate  66 ; 
     FIGS.  4 ( a ) and  4 ( b ) show the operation of a transmission shaft (1); 
     FIGS.  5 ( a ) and  5 ( b ) show the operation of the transmission shaft (2); 
     FIGS.  6 ( a ) and  6 ( b ) show the configuration of a clutch actuator; 
       FIG. 7  is a sectional view showing another embodiment of the pedal effort transmission shown in  FIG. 1 ; 
     FIGS.  8 ( a ) and  8 ( b ) are sectional views showing a roller one-way mechanism; 
     FIGS.  9 ( a ) and  9 ( b ) are sectional views showing a hollow shaft; 
       FIG. 10  is a perspective view showing a roller of the roller one-way mechanism; 
       FIG. 11  is a perspective view showing a rock spring of the roller one-way mechanism; 
       FIG. 12  shows the configuration of a main part of the roller one-way mechanism; 
       FIG. 13  shows the fitted position of each cam guide at each shift stage and correspondence among each transmission gear of the first and third transmission shafts with transmission gears mutually coupled; and 
     FIGS.  14 ( a )- 14 ( b ) are explanatory drawings for explaining the operation of the third transmission shaft. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the drawings, preferred embodiments of the invention will be described in detail below.  FIG. 1  is a side view showing a bicycle provided with a transmission equivalent to one embodiment of the invention. 
   A body frame  2  of a bicycle  1  is composed of a head pipe  20 , a main frame  21  extending diagonally downwardly and rearwardly from the head pipe  20  forkedly right and left and a swing arm  23  supported by a reciprocating shaft  22  provided to the rear of the main frame  21  so that the swing arm can move vertically. A reinforcing pipe  24  is provided under the main frame  21 . The reinforcing pipe  24  and the main frame  21  are coupled via a bracket  25  and a reinforcing member  39 . The swing arm  23  may be a rear fork. 
   A rear wheel  3 R is supported by the rear end of the swing arm  23 . A front fork  4  is supported by the head pipe  20  so that the front fork  4  can steer the bicycle  1 . The front fork  4  is an inverted type in which an outer tube and an inner tube are combined and the outer tube is located over the inner tube. A steering handlebar  5  is provided above the front fork  4  and a front wheel  3 F is supported by a lower part of the front fork. 
   The main frame  21  and the reinforcing pipe  24  are coupled in respective lower parts via the coupling member  39 . A pedal effort transmission device  6  is supported by the coupling member  39 . The pedal effort transmission device  6  includes a transmission that transmits the revolution of a crankshaft  61  to the rear wheel  3 R. A pedal  9  is attached to the crankshaft  61  via a crank  8 . A pair of right and left cranks  8  and pedals  9  are provided to the crankshaft  61 . 
   A bracket  231  is provided to the swing arm  23 , a bracket  211  is provided to the main frame  21  and a cushion member  18  for relieving shock when the swing arm  23  is turned upwardly is provided between the brackets  231  and  211 . Working fluid is supplied from a reservoir tank  19  to the cushion member  18 . 
   A rear fender  30  is attached to the main frame  21  and a seat  31  is mounted on the rear fender  30  and the main frame  21 . The rear fender  30  can be made of light material such as carbon fibers. Disc brakes  32 ,  33  are provided to the front wheel  3 F and the rear wheel  3 R. A transmission operating cable  101  extends from a speed change lever not shown and is mounted on the steering handlebar  5  and extends to the pedal effort transmission device  6  along the reinforcing pipe  24 . 
     FIG. 2  is a sectional view showing the pedal effort transmission device  6  viewed along a line I—I in  FIG. 1 , the pedal effort transmission device is mainly composed of a constant-mesh type transmission  60  and the crankshaft  61  and the transmission  60  is composed of transmission shafts  63 ,  65 ,  67  which are arranged in parallel wherein each of which supports plural transmission gears in a row. 
   Both ends of the crankshaft  61  are supported by ball bearings  681 ,  691  so that the crankshaft can be turned. The respective outer races of the ball bearings  681 ,  691  are press-fitted into a right case half  68  and a left case half  69 . A pedal sprocket  611  coaxially pierces the substantial center of the crankshaft  61 . 
   In the transmission  60 , the first transmission shaft  63  includes a hollow rotation shaft  630  with a rod-shaped clutch actuator  631  which supports the hollow shaft  630  so that the hollow shaft can be turned and which is supported so that the clutch actuator cannot be turned. Transmission gears  632 ,  633 ,  634  are supported by the hollow shaft  630  via each clutch mechanism (each ratchet one-way mechanism in this embodiment)  632   a ,  633   a ,  634   a . A driven sprocket  635  is fixedly inserted into the hollow shaft  630  with pin members  636 ,  637  which pierce the side wall of the hollow shaft  630  and which are supported so that the pin members can move vertically. A cam guide  638  is provided to one end of the clutch actuator  631 . 
   Both ends of the hollow shaft  630  are supported by ball bearings  682 ,  692  so that the hollow shaft can be turned. The respective outer races of the ball bearings  682 ,  692  are press-fitted into the right case half  68  and the left case half  69 . The driven sprocket  635  of the first transmission shaft  63  and the pedal sprocket  611  of the crankshaft  61  are coupled via a chain  601  without an end. 
   Passages  881 ,  882  are provided to the clutch actuator  631  and a concave portion on the outside face of the clutch actuator  631  communicates with the outside via each passage. As a result, as a problem with the variation of internal pressure is solved, a variation of the volume of the concave portion on the outside face by the vertical motion of the pin members  636 ,  637 , a satisfactory shift field is acquired. 
   The second transmission shaft  65  of the transmission  60  is mainly composed of a cylindrical hollow shaft  650  and transmission gears  652 ,  653 ,  654  fixedly supported by the periphery of the hollow shaft  650 . Both ends of the hollow shaft  650  are supported by ball bearings  683 ,  693  so that the hollow shaft can be turned. The respective outer races of the ball bearings  683 ,  693  are press-fitted into the right case half  68  and the left case half  69 . 
   The third transmission shaft (the output shaft)  67  of the transmission  60  includes a hollow shaft  670  with a rod-shaped clutch actuator  671  which supports the hollow shaft  670  so that the hollow shaft can be turned and which is supported so that the clutch actuator cannot be turned. Transmission gears  672 ,  673 ,  674  are supported by the hollow shaft  670  via each ratchet one-way mechanism  672   a ,  673   a ,  674   a . Pin members  676 ,  677  pierce the side wall of the hollow shaft  670  and are supported so that the pin members can move vertically. A cam guide  678  is provided to one end of the clutch actuator  671  and a driving sprocket  679  coupled to the other end of the hollow shaft  670 . 
   Both ends of the hollow shaft  670  are supported by ball bearings  684 ,  694  so that the hollow shaft can be turned. The respective outer races of the ball bearings  684 ,  694  are press-fitted into the right case half  68  and the left case half  69 . Passages  883 ,  884  are provided to the clutch actuator  671 . 
   A control face  661  is provided along the outside face of a shift plate  66  and is fitted to each cam guide  638 ,  678  of the first and third transmission shafts  63 ,  67 . The shift plate  66  is supported by a rotation shaft  662  fixedly arranged on an extended line of the hollow shaft  650  so that the shift plate can be turned. A cable hanger  64  for fitting a nipple of the transmission operating cable  101  is inserted into the end of the shift plate  66 . The shift plate  66  is constantly pressed on the side (in a shift up direction) reverse to a direction in which the operating cable is turned (a shift down direction) by a return spring  664  one end of which is fitted to a flange of the rotation shaft  662 . The other end of a lost motion spring  663  one end of which is fitted to the shift plate  66  is fitted to the cable hanger  64 . 
   The lost motion spring  663  enables a lost motion of the shift plate  66  when the cable hanger  64  is turned in the shift down direction. The return spring  664  enables a lost motion of the shift plate  66  when the cable hanger  64  is turned in the shift up direction. 
   FIGS.  3 ( a )- 3 ( c ) show the structure of the shift plate  66 . FIG.  3 ( a ) is a front view, FIG.  3 ( b ) is a sectional view viewed along a line B—B in FIG.  3 ( a ) and FIG.  3 ( c ) is an expansion plan showing a control face  661  provided on its outside face in a circumferential direction. 
   The axial position of the control face  661  is different depending upon positions  1  (M) to  7  (M) and  1  (D) to  7  (D) as shown in FIG.  3 C. The positions  1  (M) to  7  (M) are fitted to the cam guide  638  of the first transmission shaft  63  and the positions  1  (D) to  7  (D) are fitted to the cam guide  678  of the third transmission shaft  67 . For the number of shifts, if each cam guide  638 ,  678  is fitted to  1  (M),  1  (D), the number of shifts is one, if each cam guide is fitted to  2  (M),  2  (D), the number is two and if each cam guide is fitted to  7  (M),  7  (D), the number is seven. 
   FIGS.  4 ( a )- 4 ( b ) and  5 ( a )- 5 ( b ) are side views viewed along the transmission shaft and sectional views viewed along a line I—I for explaining the clutch mechanisms of the first transmission shaft  63  and the third transmission shaft  67 . The same reference number denotes the same or the similar part. 
   The operation in the case of shift down from a fifth stage (the state shown in  FIG. 2 ) to a fourth stage and operation in the case of shift up to a sixth stage will be described based upon the first transmission shaft  63  below. 
   As shown in FIGS.  6 ( a )- 6 ( b ) in detail, wherein FIG.  6 ( b ) is a cross-section along the line IV—IV in FIG.  6 ( a ), a cam part in which a cam crest  631   a  and a cam groove  631   c  continue is formed on the outside face of the clutch actuator  631 . An inclined face  631   b  connecting the cam crest  631   a  and the cam groove  631   c  is formed in a boundary between the cam crest and the cam groove in a circumferential direction. 
   When the number of shifts is five, the cam guide  638  of the first transmission shaft  63  is fitted to the position  5  (M) shown in  FIG. 3C , the cam guide  678  of the third transmission shaft  67  is fitted to the position  5  (D) and as a result, as described in detail later, the first transmission gear  632  of the first transmission shaft  63  and the second gear  673  of the third transmission shaft are coupled via the second transmission shaft. 
     FIG. 13  shows the fitted position of each cam guide  638 ,  678  at each shift stage 1 to 7 and the correspondence of each transmission gear of the mutually coupled first and third transmission shafts  63  and  67  via the second transmission shaft  65 , for example, at a second stage except the fifth stage. The cam guide  638  of the first transmission shaft  63  is fitted to the position  2  (M) of the control face  661  and the cam guide  678  of the third transmission shaft  67  is fitted to the position  2  (D). As a result, the third gear  634  of the first transmission shaft  63  is coupled to the second transmission gear  673  of the third transmission shaft  67  via the second transmission shaft  65 . 
   As the pin members  636  and  637  are both located in the cam groove  631   c  of the clutch actuator  631  in the first transmission shaft  63  as shown in FIG.  4 ( a ) when the number of shifts is five as shown in  FIG. 2 , the free ends  632   c  of a pair of ratchet pawls  632   b  are rocked in a central direction for the first transmission gear  632  as shown in FIG.  4 ( b ) and are fitted to gear teeth  630   a  provided on the outside face of the hollow shaft  630  in a direction of normal rotation. Similarly, the second and third transmission gears  633  and  634  are also engaged with the gear teeth  630   a  of the hollow shaft  630  in the direction of normal rotation. Therefore, if the hollow shaft  630  is revolved in a direction shown by an arrow B according to pedal effort input to the driven sprocket  635 , all the transmission gears  632 ,  633  and  634  are revolved in the direction shown by the arrow B in synchronization with it. 
   However, as the second transmission shaft  65  is turned at the highest speed by a driving force transmitted from the first transmission gear  632  of the first transmission shaft  63  to the first transmission gear  652  of the second transmission shaft, only the driving force transmitted from the first transmission gear  632  of the first transmission shaft  63  acts upon the second transmission shaft  65  as also shown in  FIG. 13 , and the second and third transmission gears  633  and  634  are substantially raced by their clutch mechanisms. 
   At this time, as the pin member  676  is located in the cam groove of the clutch actuator  671  and the pin member  677  is located on the cam crest of the clutch actuator  671  in the third transmission shaft  67  as shown in FIG.  14 ( a ), only the ratchet one-way mechanisms  672   a  and  673   a  of the first and second transmission gears  672  and  673  are turned on and are fitted to the hollow shaft  670  in the direction of normal rotation. However, as the second transmission gear  673  has a smaller diameter and the first transmission gear  672  becomes free, pedal effort input to the sprocket  635  is transmitted to the driving sprocket  679  via the first transmission gear  632  of the first transmission shaft  63 , the second transmission shaft  65  and the second transmission gear  673  of the third transmission shaft  67 . 
   As a shift operation cable  101  is pulled out when a rider executes shift down operation to the fourth stage, working the pedal, the shift plate  66  is turned against the elastic force of the return spring  664 . By the shift operation, the clutch actuator  631  of the first transmission shaft  63  is axially displaced by a cam mechanism composed of the control face  661  and the cam guide  638 . When the clutch actuator  631  is displaced by distance ΔL1 as shown in FIG.  4 ( b ), the pin member  636  reaches an entrance of the inclined face  631   b  of the clutch actuator  631  and further, starts to advance on the inclined face  631   b  as the hollow shaft  630  is turned. 
   In case when the rider swiftly makes a shift operation and frequently makes a shift operation or in case when the revolution speed of the crankshaft is small as in a case that the bicycle goes up on a slope and the axial traveling speed of the clutch actuator  631  for the hollow shaft  630  is limited, the revolution speed of the shift plate  66  cannot follow the revolution speed of the cable hanger  64  and elastic force according to phase difference between both is stored in the lost motion spring  663 . 
   Afterward, the pin member  636  starts to go up on the inclined face  631   b  by interaction between the elastic force stored in the lost motion spring  663  and the inclined face  631   b  as shown in FIG.  5 ( a ) if pedal effort is input and when the pin member  636  further advances, it climbs on the cam crest  631   a  of the clutch actuator  631  as shown in FIG.  5 ( b ). As a result, as the free end  632   c  of the ratchet pawl  632   b  is radially pushed up by the pin member  636 , the fitting between the first transmission gear  632  and the hollow shaft  630  is released and only the transmission gears  633  and  634  can maintain the fitting to the hollow shaft  630 . 
   At this time, the third transmission shaft  67  is also displaced by ΔL1 and the cam guide  678  is fitted to the position  4  (D) of the control face  661 . However, as the position  4  (D) is the same as the position  5  (D), the engagement of the third transmission shaft  67  is unchanged. As a result, as the diameter of the second transmission gear  673  is smaller than that of the first transmission gear  672  though the respective clutch mechanisms of the first and second transmission gears  672  and  673  are turned on and the clutch mechanism of the third transmission gear is turned off in the third transmission shaft  67 , the first transmission gear  672  becomes free. Therefore, pedal effort input to the sprocket  635  is transmitted to the driving sprocket  679  via the second transmission gear  633  of the first transmission shaft  63 , the second transmission shaft  65  and the second transmission gear  673  of the third transmission shaft  67 . 
   In the meantime, as the shift operation cable  101  is pulled in by the elastic force of the return spring  664  when the rider executes a shift up operation to a sixth stage, the shift plate  66  is turned in a direction reverse to the direction in shift down. The clutch actuator  631  of the first transmission shaft  63  is axially displaced by the cam mechanism composed of the control face  661  and the can guide  638  according to the shift operation and the cam guide  638  is fitted to the position  6  (M) of the control face  661 . 
   In this embodiment, as shown in FIG.  3 ( c ), as the position  6  (M) and the position  4  (M) of the control face  661  are the same, the clutch actuator  631  and the pin members  636 ,  637  are operated as in the shift down to the fourth stage. 
   As elastic force according to phase difference between both is stored in the return spring  646  in this embodiment when the revolution speed of the shift plate  66  cannot follow the revolution speed of the cable hanger  64  because the operation is swiftly executed in shift up, a lost motion of the shift plate  66  is enabled as described above. 
   As the pin member  677  also drops in the cam groove of the clutch actuator  671  in the third transmission shaft  67  as shown in FIG.  14 ( b ), the ratchet one-way mechanisms  672   a ,  673   a  and  674   a  of all the transmission gears  672 ,  673  and  674  are turned on. However, as the diameter of the third transmission gear  674  is the smallest in the third transmission shaft  67 , the other transmission gears  672  and  673  become free. Therefore, pedal effort input to the sprocket  635  is transmitted to the driving sprocket  679  via the second transmission gear  633  of the first transmission shaft  63 , the second transmission shaft  65  and the third transmission gear  674  of the third transmission shaft  67  as also shown in FIG.  13 . 
   As described above, according to this embodiment, as the clutch actuator  631  can be housed in the hollow shaft  630 , the constant-mesh type transmission the axial miniaturization of which is enabled by the simple configuration can be also realized in a drive line in which a shaft itself is revolved. 
   Also, in this embodiment, as the inclined face  631   b  connecting the cam groove  631   c  and the cam crest  631   a  is circumferentially provided to the irregular cam part formed on the outside face of the clutch actuator  631  and the pin member can be carried from the cam groove  631   c  to the cam crest  631   a  by a small force and smoothly, speed can be changed even if pedal effort is applied to the crankshaft. 
   Further, according to this embodiment, as a shift operation is held in the lost motion spring  663  (in shift down) or the return spring  646  (in shift up) as elastic force in case a shift mechanism cannot follow the shift operation and afterward, the shift mechanism executes shift by the elastic force, secure shift is enabled even if shift operation is swiftly made, shift operation is made a plurality of times or shift operation is made in a low-speed operation. Therefore, a condition related to shift timing is relaxed and a shift degree of freedom is high is enabled. 
     FIG. 7  is a sectional view showing a second embodiment of the pedal effort transmission and the same reference number denotes the same or the similar part. 
   In the first embodiment, the case in which the ratchet one-way mechanism is adopted for the clutch mechanism for fitting the clutch actuators  631  and  671  of the first and third transmission shafts  63  and  67  and each transmission gear or releasing the fitting is described. However, in this embodiment a roller one-way mechanism is adopted in place of the ratchet one-way mechanism.  FIG. 7  shows a state of four stages. 
   In a transmission  70 , a first transmission shaft  73  is mainly composed of a cylindrical hollow shaft  730 , a rod-shaped clutch actuator  731  inserted into the hollow shaft  730 , transmission gears  632 ,  633 ,  634  supported by the hollow shaft  730  via a roller one-way mechanism as a clutch mechanism, a sprocket  635  fixedly inserted into the hollow shaft  730 , pin members  636 ,  637  piercing the side wall of the hollow shaft  730  and supported so that the pin member can move vertically and a cam guide  638  provided to one end of the clutch actuator  731 . 
   Both ends of the hollow shaft  730  are supported by ball bearings  682 ,  692  so that the hollow shaft can be turned. The outer race of each ball bearing  682 ,  692  is press-fitted into a right case half  68  and a left case half  69 . The sprocket  635  of the first transmission shaft  73  and a pedal sprocket  611  of a crankshaft  61  are coupled by a chain  601  without an end. Passages  885 ,  886  are provided to the clutch actuator  731 . 
   A second transmission shaft  75  of the transmission  70  is provided with a similar configuration to the second transmission shaft  65  in the first embodiment. A third transmission shaft  77  of the transmission  70  is also provided with a similar configuration to the third transmission shaft  67  in the first embodiment except that its clutch mechanism is a roller one-way mechanism and a rod-shaped clutch actuator  771  is inserted into a hollow shaft  770 . Passages  886 ,  887  are provided to the clutch actuator  771 . 
   FIGS.  8 ( a ) and  8 ( b ) are sectional views showing the structure of the roller one-way mechanism, FIG.  9 ( a ) is a sectional view viewed along the axis of the hollow shaft  730 , FIG.  9 ( b ) is a sectional view viewed along a line V—V in FIG.  9 ( a ) and the same reference number denotes the same or the similar part. 
   As shown in FIG.  9 ( b ), the hollow shaft  730  is provided with six slits  730   a  at an equal interval in an axial direction of the outside face and an opening  730   b  linked with a central hole is formed on the side of one end of the bottom of each slit  730   a . The side of one end on which the opening  730   b  is formed of the bottom of the slit  730   a  is shallower than the side of the other end. 
   As shown in FIGS.  8 ( a ) and  8 ( b ), in each slit  730   a  of the hollow shaft  730 , plural (three in this embodiment) rollers  741  are housed axially in a line and a pin member  676  is housed in each opening  730   b  so that the pin member can move vertically. As shown in  FIG. 10 , an annular groove  741   a  is formed on the circumference in the center of the roller  741 . A rock spring  742  that elastically presses the roller  741  on the side of the other side wall in the slit is inserted into one of the opposite side walls of each slit  730   a.    
     FIG. 11  is a perspective view showing the configuration of the rock spring  742  and in this embodiment, a plane part acquired by fitting respective one principal planes of a pair of L-type springs  742   a ,  742   b  and legs which are respective other principal planes of a pair of L-type springs and support the plane part by each one end and each other end are included.  FIG. 12  shows the relative positional relation of the rock spring  742 , the roller  741  and the pin member  636  respectively viewed from another angle. 
   In such a configuration, the pin member  636  vertically moves according to an axial position of the clutch actuator  731  as described above, in a state in which the pin member  636  is lowered. Each roller  741  is elastically pressed from a deep position to a shallow position in each slit  730   a  by each rock spring  742  clockwise as shown in FIG.  8 ( a ). Therefore, as the outside face of the hollow shaft  730  and the inside face of the transmission gear  632  are fitted via the roller  741 , the transmission gear  632  is also revolved in a direction shown by an arrow B in synchronization when the hollow shaft  730  is revolved in the direction shown by the arrow B according to pedal effort input to the driven sprocket  635 . 
   In the meantime, in a state in which the pin member  636  is lifted, each roller  741  is pushed back counterclockwise against the resilience of each rock spring  742  by the pin member  636  as shown in FIG.  8 ( b ) and is moved from the shallow position to the deep position in each slit of the hollow shaft  730 . As a result, as the fitting of the hollow shaft  730  and the transmission gear  632  via the roller  741  is released, the transmission gear  632  is not revolved even if the hollow shaft  730  is revolved in the direction shown by the arrow B according to pedal effort input to the driven sprocket  635 . 
   According to this embodiment, as not only the similar effect to that in the first embodiment is acquired but the lash is smaller in roller on-way structure, compared with that in the ratchet one-way structure, shock and a lash at a pedal when speed is changed, inputting pedal effort can be greatly reduced. 
   According to the invention, the following effect is acquired. 
   (1) As the clutch actuator can be housed in the hollow shaft, the constant-mesh type transmission which has a simple configuration and in which axial miniaturization is enabled can also be realized in a drive line in which a shaft itself is revolved. 
   (2) In the constant-mesh type transmission in which the clutch actuator is housed in the shaft, the clutch mechanism can be realized by a simple configuration. As plural clutch actuators are operated by one cam mechanism, each clutch actuator can be simply and precisely synchronized and as a result, satisfactory shift feeling is acquired. 
   (3) As the pin member of the clutch mechanism can be lifted from the cam groove to the cam crest respectively formed on the surface of the clutch actuator by a small force and smoothly, shift is also enabled in a state in which pedal effort is applied. 
   (4) In the case when the shift mechanism cannot follow the shift operation, the shift operation is held in the lost motion spring or the return spring as an elastic force and afterward, as the shift mechanism executes shift by the elastic force, secure shift is enabled even if a shift operation is swiftly made, shift operation is made a plurality of times or shift operation is made in a low-speed operation. Therefore, a condition related to shift timing is relaxed and a degree of freedom of the shift is high is enabled. 
   (5) In case the roller one-way structure is adopted as the clutch mechanism, shock and a lash at the pedal when speed is changed, inputting pedal effort can be greatly reduced, compared with the case when the ratchet one-way structure is adopted as the clutch mechanism. 
   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 departure 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.