Abstract:
In an oil passage structure in a rotary shaft, including two systems of oil passages different in pressure that are provided extending from both ends of the shaft, the rotary shaft is provided with oil supply holes in the radial direction of the shaft for connection between a center hole in the shaft and locations to be supplied with oil. The oil supply holes are bored from the outside of the shaft. At this time, burrs are generated at end portions of the oil supply holes on the side fronting on the center hole. Where the depth of the shaft center hole is a dead end, removal of the burrs is not easy. The shaft center hole is used as an oil passage wherein burrs, if any, in the hole can be easily removed. The two oil passages are in communication with each other through a communication passage smaller than the oil passages in diameter. The smaller-diameter communication passage is closed by pressing a steel ball therein, thereby making both of the oil passages independent from each other.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present nonprovisional application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-342918 filed on Nov. 8, 2001 the entire contents thereof is hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an oil passage structure in a rotary shaft that is applied to a transmission of an internal combustion engine-transmission integrated type power unit for a four-wheel buggy car (saddle ride type vehicle for operating on wasteland). 
   2. Description of Background Art 
   There has hitherto been practiced a technology in which center holes extending along the center line of a rotary shaft are provided that extend from both ends of the rotary shaft. Oil supply holes are provided for connecting the center holes with portions requiring oil supply. Oil that is different in pressure, namely, a high-pressure working oil for an oil hydraulic clutch and a low-pressure lubricating oil are supplied, respectively, from both ends of the rotary shaft. Thus, two systems of oil passages are formed. Since it is necessary to supply the oil at different pressures into the center holes, the depths of the center holes bored from both ends of the shaft have hitherto been so set that the center holes are not in communication with each other in the shaft in the boring step. Therefore, the center holes have been partitioned from each other by the material of the shaft itself. Namely, the depth bottom portions of the center holes have each been machined into a dead end shape. 
   Oil supply holes extending in the radial direction of the rotary shaft for connecting the center holes of the shaft with portions requiring oil supply are bored in the rotary shaft from outside of the shaft. At this time, so-called burrs are generated at an end portion of each oil supply hole on the side fronting on the center hole. In the case of the center hole having the above-mentioned dead end shape, it is difficult to perform deburring, and much time has been required for the deburring step. 
   SUMMARY AND OBJECTS OF THE INVENTION 
   It is an object of the present invention to provide a structure for shaft center holes used as oil passages in which it is possible to easily remove burrs, which may be generated in the holes. 
   The present invention has solved the above-mentioned problem. The present invention pertains to an oil passage structure in a rotary shaft, including two systems of oil passages that are different in pressure. The oil passages are provided to extend from both ends of the shaft, wherein the two oil passages are in communication with each other through a communication passage that is smaller than the oil passages in diameter. The smaller-diameter communication passage is closed by pressing a steel ball therein. 
   According to the present invention as constituted above, after the machining of the center holes and radial oil supply holes and before the pressing-in of the steel ball, both the center holes are in a condition of mutually communication with each other. Thus, it is easy to remove burrs present in the center holes. In addition, by the pressing-in of the steel ball, the high-pressure oil passage and the low-pressure oil passage can be easily separated from each other. 
   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 of a four-wheel buggy car (saddle ride type vehicle for operating on wasteland) on which an internal combustion engine according to the present invention is mounted; 
       FIG. 2  is a front view of a power unit according to the present invention; 
       FIG. 3  is a view of a front crankcase cover from the front side; 
       FIG. 4  is a view of a front crankcase from the front side; 
       FIG. 5  is a vertical sectional view of the inside of a crankcase, showing the relationship between a crankshaft and a main shaft; 
       FIG. 6  is a vertical sectional view of the inside of the crankcase, showing the relationship among the main shaft, a counter shaft, an intermediate shaft, and an output shaft; 
       FIG. 7  is an enlarged sectional view for illustrating the constitution and actions of a first gear position oil hydraulic type multiple disk clutch and a first gear position driving gear; and 
       FIG. 8  is a vertical sectional view of an oil passage for supplying a lubricating oil. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a side view of a four-wheel buggy car (saddle ride type vehicle for operating on wasteland) on which an internal combustion engine with an oil hydraulic type automatic transmission according to the present invention is mounted. The buggy car has a structure in which left-right pairs of front wheels  2  and rear wheels  3  are provided, respectively, at front and rear portions of a vehicle body frame  1 , and a power unit  6  integrally constituting an internal combustion engine  4  and a transmission  5  is supported on a central portion of the vehicle body frame  1 . The power unit  6  is disposed with a crankshaft  7  directed in the front-rear direction of the vehicle body. The rotation of the crankshaft  7  is transmitted through a main shaft  8 , a counter shaft  9 , and an intermediate shaft  10  (all shown in  FIG. 4 ) of the transmission to an output shaft  11 . These shafts are all parallel to the crankshaft, and are disposed in the front-rear direction of the vehicle body. The front wheels  2  are driven by a front wheel drive shaft  12  connected to the front end of the output shaft  11 , while the rear wheels  3  are driven by a rear wheel drive shaft  13  connected to the rear end of the output shaft  11 . A steering handle  14 , a fuel tank  15 , and a saddle type seat  16  are provided, in this order from the front side, at upper portions of the vehicle body. 
     FIG. 2  is a front view of the power unit  6  according to the present invention, in which the front surface of the power unit  6  is viewed from the front side. A main body portion of the power unit  6  is generally composed of four portions, namely, a cylinder head cover  20 , a cylinder head  21 , a cylinder block  22  and a crankcase  23 , in this order from the upper side. In addition, the crankcase  23  is divided in a plane orthogonal to the crankshaft  7  into four portions, for forming a front crankcase cover  24 , a front crankcase  25 , a rear crankcase  26  and a rear crankcase cover  27  (these are partially shown in  FIGS. 5 ,  6 , and  8 ), in this order from the front side. In  FIG. 2 , the front crankcase cover  24  is illustrated and the front crankcase  25  is a somewhat illustrated a little in the surroundings thereof. Various equipment and piping are fitted to a front surface of the front crankcase cover  24 .  FIG. 3  is a view of only the front crankcase cover  24  from the front side, and  FIG. 4  is a view of the front crankcase  25  from the front side. 
     FIG. 4  shows the positions of the crankshaft  7 , the main shaft  8 , the counter shaft  9 , the intermediate shaft  10 , and the output shaft  11  of the transmission.  FIGS. 5 ,  6 , and  8  are vertical sectional views of the inside of the crankcase passing through main shafts in the crankcase, in which  FIG. 5  shows the relationship between the crankshaft  7  and the main shaft  8 ,  FIG. 6  shows the relationship among the main shaft  8 , the counter shaft  9 , the intermediate shaft  10 , and the output shaft  11 , and  FIG. 8  shows the relationship between the main shaft  8 , the counter shaft  9 , and the intermediate shaft  10 , and lubricating oil supply oil passages. In these figures, arrow F indicates the front or forward direction. 
     FIG. 5  shows a power transmission mechanism between the crankshaft  7  and the main shaft  8 . The crankshaft  7  is supported on the front and rear crankcases  25  and  26  through bearings. A front extended portion of the crankshaft  7  is supported on the front crankcase cover  24  through a bearing. The crankshaft  7  is divided into front and rear portions, which are connected by a crank pin  7   b  at a crank web  7   a . An AC generator  28  for generating power by rotation of the crankshaft  7  is fitted to the rear end of the crankshaft  7 . 
   The crankshaft  7  is provided with a primary driving gear  31  through a torque converter  30 . The primary driving gear  31  is rotatably supported on the crankshaft  7  through a needle bearing  32 . The torque converter  30  includes a pump impeller  33  fixed to the crankshaft  7 , a turbine runner  34  opposed thereto, and a stator  35 . The primary driving gear  31  rotatable in relation to the crankshaft  7  is connected to the turbine runner  34 , and power from the crankshaft  7  is transmitted to the primary driving gear  31  through the working oil. A primary driven gear  36  constantly meshed with the primary driving gear  31  is fixed to a front end portion of the main shaft  8  of the transmission. The rotation of the crankshaft  7  is transmitted to the main shaft  8  through primary speed reduction performed by the primary driving gear  31  and the primary driven gear  36 . 
     FIG. 6  shows a power transmission mechanism among the main shaft  8 , the counter shaft  9 , the intermediate shaft  10 , and the output shaft  11  of the transmission. The main shaft  8  of the transmission is supported on the front and rear crankcases  25  and  26  through bearings. The main shaft  8  is provided with a first gear position driving gear  40 , a second gear position driving gear  41  and a third gear position driving gear  42 , which differ in the number of teeth according to speed reduction ratios. The second gear position driving gear  41  and the third gear position driving gear  42  are fixed gears, which are fixed on the main shaft  8 , while the first gear position driving gear  40  is rotatably supported on the main shaft  8  through a needle bearing  43 . In the description below, generally, a gear rotatably supported on a rotary shaft through a needle bearing is called a floating gear. A first gear position oil hydraulic type multiple disk clutch  44  is intermediately provided between the main shaft  8  and the first gear position driving gear  40 . 
     FIG. 7  is an enlarged sectional view for illustrating the constitution and actions of the first gear position oil hydraulic type multiple disk clutch  44  and the first gear position driving gear  40 . The first gear position oil hydraulic type multiple disk clutch  44  is composed of a vessel form clutch outer  46  fixed to the main shaft  8  through an outer cylinder  45 . An annular stopper  47  is fixed to an open end of the clutch outer  46  with outside clutch disks  48  held on an inner peripheral surface of the clutch outer through splines so as to be displaceable in the axial direction. A pressure plate  49  is fitted in a piston form adjacently to a bottom wall portion  46   a  of the clutch outer  46  with a coil spring  51  provided between a locking portion  50  provided on the clutch outer  46  and the pressure plate  49  for pressing the pressure plate  49  towards the bottom wall portion  46   a  of the clutch outer  46 . A clutch inner  52  is fitted integrally to the first gear position driving gear  40  with inside clutch disks  53  held on an outer peripheral surface of the clutch inner  52  through splines so as to be displaceable in the axial direction and arranged alternately with the outside clutch disks  48 . A working oil supply hole  54  in the first oil hydraulic type multiple disk clutch  44  is provided so as to connect the main shaft  8 , the outer cylinder  45 , and the clutch outer  46  with lubricating oil supply holes  55  for the needle bearing  43  for the first gear position driving gear  40 . The main shaft  8  is provided with a center hole with an inside diameter varied steppedly on the center line thereof. A steel ball  56  is press fitted in the narrowest portion of the center hole, whereby the center hole is partitioned into a front portion center hole  57  and a rear portion center hole  58 . 
   As shown in  FIG. 6 , the working oil for the clutch  44  is fed from the side of the front crankcase cover  24  to the front portion center hole  57  through a working oil supply pipe  59  and is supplied to the clutch  44  through the working oil supply hole  54 . As shown in  FIG. 7 , as the working oil comes between the bottom wall portion  46   a  of the clutch outer  46  and the pressure plate  49 , the oil pressure causes the pressure plate  49  to move against an energizing force of the coil spring  51 , the inside and outside clutch disks are pressed in the axial direction and the outside clutch disks  48  restricts the movement of the inside clutch disks  53 . By this arrangement, the clutch inner  52  is integrated with the clutch outer  46 , the first gear position driving gear  40  does not float but is fixed to the main shaft  8  and the rotation of the main shaft  8  is transmitted to the first gear position driving gear  40 . A lubricating oil for the needle bearing  43 , which bears the first gear position driving gear  40 , is supplied from the side of the rear portion center hole  58  through the lubricating oil supply hole  55 . 
   The counter shaft  9  includes a front portion counter shaft  9   a  and a rear portion counter shaft  9   b , which are integrated with each other to form the counter shaft  9 . The counter shaft  9  is supported on the front crankcase  25 , the rear crankcase  26 , and the rear crankcase cover  27  through bearings. The front portion counter shaft  9   a  is provided with a first gear position driven gear  60 , a second gear position driven gear  61 , and a third gear position driven gear  62 , which are constantly meshed, respectively, with the first gear position driving gear  40 , the second gear position driving gear  41  and the third gear position driving gear  42  on the main shaft  8 . The first gear position driven gear  60  is a fixed gear fixed to a shaft, while the second gear position driven gear  61  and the third gear position driven gear  62  are floating gears, which are supported rotatably in relation to the counter shaft  9  through needle bearings  63  and  64 , respectively. A second gear position oil hydraulic type multiple disk clutch  65  and a third gear position oil hydraulic type multiple disk clutch  66  are intermediately provided between the counter shaft  9  and these floating gears, respectively. In these clutches, a clutch outer is fixed to the counter shaft  9 , and a clutch inner is connected to the floating gear. The constitution and actions of these clutches are the same as those of the above-mentioned first gear position oil hydraulic type multiple disk clutch  44 . Therefore, a detailed description thereof is omitted. Also in these clutches, a working oil is supplied through working oil supply holes  67  and  68  formed in the counter shaft, whereby floating of the floating gears is stopped, to enable transmission of power, thereby performing a speed reduction at the second gear position or the third gear position. Lubricating oil supply holes  69  and  70  leading to the needle bearings  63  and  64  for bearing the second gear position driven gear  61  and the third gear position driven gear  62  are also formed in the counter shaft  9 . 
   The rear portion counter shaft  9   b  is provided with a forward-running driving gear  71  and a backward-running driving gear  72 . These are both floating gears, of which the one engaged with a manual dog clutch  73  provided at an intermediate position therebetween is fixed to a shaft, whereby transmission of power is enabled. Lubricating oil supply holes  76  and  77  for supplying a lubricating oil to needle bearings  74  and  75  respectively bearing the forward-running driving gear  71  and the backward-running driving gear  72  are formed in the rear portion counter shaft  9   b.    
   The counter shaft  9  includes the front portion counter shaft  9   a  and the rear portion counter shaft  9   b  integrated with each other and provided with a center hole, which is partitioned into a front portion center hole  79  and a rear portion center hole  80  by a steel ball  78  press fitted in a narrowest portion thereof. The supply of a working oil to the second and third gear position oil hydraulic type multiple disk clutches  65  and  66  is conducted from the side of the front crankcase cover  24  through a double-wall pipe  81 . The double-wall pipe  81  includes an outer pipe  81   a  and an inner pipe  81   b . The working oil for the second gear position oil hydraulic type multiple disk clutch  65  is supplied through an oil passage between the outer pipe  81   a  and the inner pipe  81   b  and through the working oil supply hole  67 . The working oil for the third gear position oil hydraulic type multiple disk clutch  66  is supplied through an oil passage inside the inner pipe  81   b  and the working oil supply hole  68 . The working oil for the needle bearing  63  for the second gear position driven gear  61  is supplied from the side of the front crankcase  25  through an oil passage between the front portion counter shaft  9   a  and the outer pipe  81   a  and through the lubricating oil supply hole  69 . The working oil supplied to the needle bearings  64 ,  74 , and  75  for the third gear position driven gear  62 , the forward-running driving gear  71  and the backward-running driving gear  72  is supplied from the side of the rear crankcase cover  27  through the rear portion center hole  80  of the counter shaft  9  and the lubricating oil supply holes  70 ,  76 , and  77 . 
   The intermediate shaft  10  is supported on the rear crankcase  26  and the rear crankcase cover  27 . A first intermediate gear  82  is constantly meshed with the backward-running driving gear  72  and a second intermediate gear  83  is connected to the first intermediate gear  82  through a long sleeve portion  83   a  rotatably held on the intermediate shaft  10 . A lubricating oil for sliding portions of the first intermediate gear  82  and the second intermediate gear  83  for sliding in relation to the intermediate shaft  10  is supplied from the rear crankcase  26  through a center hole of the intermediate shaft and a lubricating oil supply hole  84 . 
   The output shaft  11  is supported on the front crankcase cover  24 , the rear crankcase  26 , and the rear crankcase cover  27  through bearings. The output shaft  11  pierces through the front crankcase  25  without making contact with the front crankcase  25 . An output shaft driven gear  85  constantly meshed with the forward-running driving gear  71  and the second intermediate gear  83  is fixed onto the output shaft  11 . The output shaft driven gear  85  is driven for forward operating or driven for backward operating through the gear that the dog clutch  73  is engaged, whereby the output shaft  11  is rotated in a direction suitable for forward operating or backward operating of the vehicle. Such a control is made so that the backward-running driving is connected only when the counter shaft  9  is rotating at the first gear position. 
   The gears in the above-mentioned transmission are all constantly meshed type gears, and which of speed change ratios is effected is determined by which of the oil hydraulic type multiple disk clutches  44 ,  65 , and  66  is put into the connected condition. The oil pressure control for this is performed by a valve body  90  assembled as an integral oil pressure control system by collecting the solenoid valve and oil pressure changeover valves. The position of the valve body  90  is as shown in  FIG. 2 ; namely, the valve body  90  is fitted to a front surface of the front crankcase cover  24 . The valve body  90  is fitted to a fitting recessed portion  91  of the front crankcase cover  24  shown in  FIG. 3 , and is fixed to a fitting surface  92  in the surroundings of the fitting recessed portion  91  through a gasket. In the fitted condition, a front half of the valve body  90  is exposed to the exterior of the front crankcase cover  24 , and a rear half of the valve body  90  is embedded in the fitting recessed portion  91  of the front crankcase cover  24 . The fitting surface  92  of the front crankcase cover  24  is formed to be parallel with parting faces of the crankcase. 
   Transfer of the working oil between the front crankcase cover  24  and the valve body  90  is performed between a plurality of working oil inlet/outlet ports provided in the fitting surface  92  and a plurality of working oil inlet/outlet ports provided in the fitting surface on the side of the valve body  90  at positions opposed to the former working oil inlet/outlet ports. The gasket intermediately disposed between the fitting surfaces of the valve body  90  and the front crankcase cover  24  is provided with oil passage holes at positions corresponding to the plurality of working oil inlet/outlet ports. 
     FIG. 3  shows the working oil inlet/outlet ports provided in the valve body fitting surface  92  of the front crankcase cover  24 . These are a working oil supply port  93  leading from the front crankcase cover  24  towards the valve body  90 , a working oil inlet  94  leading from the valve body  90  towards the first gear position oil hydraulic type multiple disk clutch, a working oil inlet  95  leading from the valve body  90  towards the second gear position oil hydraulic type multiple disk clutch, and a working oil inlet  96  leading from the valve body  90  towards the third gear position oil hydraulic type multiple disk clutch. 
   In  FIG. 3 , an extension position  100  of a pump shaft centerline is illustrated for an oil pump, which is not shown. The oil pump is provided between the front crankcase cover  24  and the front crankcase  25 . Oil fed from the oil pump is fed to an oil filter  103  through oil passages  101  and  102  formed in the inside of a wall surface of the front crankcase cover  24 . After foreign matter is filtered away from the oil by the filter, the oil is fed out through an oil passage  104 , and a portion of the oil is fed through the working oil supply port  93  into the valve body  90 . The other portion of the oil is fed out through an oil passage  105  and an oil passage  106  extending orthogonally to the oil passage  105  towards the front crankcase  25 , as a working oil for the torque converter or as a lubricating oil for bearing portions. 
   In  FIG. 3 , an extension position  8   a  of the center line of the main shaft  8  of the transmission is illustrated. The working oil fed out to the working oil inlet  94  leading from the valve body  90  towards the first gear position oil hydraulic type multiple disk clutch  44  is fed to the front portion center hole  57  of the main shaft  8  through the working oil supply pipe  59  provided bridgingly from a rear surface of the front crankcase cover  24  to the front portion center hole  57 , as shown in  FIG. 6 , and is supplied to the first gear position oil hydraulic type multiple disk clutch  44 . 
   In  FIG. 3 , an extension position  9   c  of the center line of the counter shaft  9  is illustrated. This portion of the front crankcase cover  24  is provided with an oil passage connection portion  107 , and oil passages  108  and  109  are formed that lead, respectively, from the working oil inlet  95  leading towards the second gear position oil hydraulic type multiple disk clutch  65  and the working oil inlet  96  leading towards the third gear position oil hydraulic type multiple disk clutch  66  to the oil passage connection portion  107 . The working oil fed from the valve body  90  to the working oil inlet  95  or the working oil inlet  96  is fed from the oil passage connection portion  107  to the front portion center hole  79  of the counter shaft  9  through either of the inner and outer passages of the working oil supply double-wall pipe  81  provided bridgingly to the front portion center hole  79 , as shown in  FIG. 6 , and is supplied to the second gear position oil hydraulic type multiple disk clutch  65  or the third gear position oil hydraulic type multiple disk clutch  66 . 
     FIG. 8  is a vertical sectional view of an oil passage for supplying the lubricating oil, which follows the oil passages  105  and  106  shown in FIG.  3 . The oil passage for supplying the lubricating oil has a structure in which oil passages bored in the surrounding portions of four portions of the crankcase, namely, the front crankcase cover  24 , the front crankcase  25 , the rear crankcase  26 , and the rear crankcase cover  27  are in communication with each other. As has been described above, the working oil for the clutches is all supplied directly from the front crankcase cover  24 ; while, on the other hand, the lubricating oil for bearing portions of the speed change gears is supplied from the oil passages in the front crankcase  25 , the rear crankcase  26 , and the rear crankcase cover  27 . 
   An oil passage  110  bored in the front crankcase  25  is an oil passage for supplying the lubricating oil to the needle bearing  63  for the second gear position driven gear  61  on the counter shaft  9  through the lubricating oil supply hole  69 . An oil passage  111  bored in the rear crankcase  26  is an oil passage for supplying the lubricating oil to the needle bearing  43  for the first gear position driving gear  40  on the main shaft  8  through the lubricating oil supply hole  55 , and for supplying the lubricating oil to a sliding portion for a shaft of the second intermediate gear  83  on the intermediate shaft  10  through the lubricating oil supply hole  84 . An oil passage  112  bored in the rear crankcase cover  27  is an oil passage for supplying the lubricating oil to the needle bearing  64  for the third driven gear  62  on the counter shaft  9  through the lubricating oil supply hole  70 , for supplying the lubricating oil to the needle bearing  74  for the forward-running driving gear  71  through the lubricating oil supply hole  76 , and for supplying the lubricating oil to the needle bearing  75  for the backward-running driving gear  72  through the lubricating oil supply hole  77 . 
   As has been detailed above, in the present embodiment, the main shaft  8  is provided with the center hole steppedly varied in inside diameter on the center line thereof, and the steel ball  56  is pressed into the narrowest portion of the center hole, whereby the center hole is partitioned into the front portion center hole  57  and the rear portion center hole  58 . The counter shaft  9  is provided with the center hole on the center line thereof, and the steel ball  78  pressed into the narrowest portion of the center hole partitions the center hole into the front portion center hole  79  and the rear portion center hole  80 . Therefore, after the machining or boring of the center holes and the radial oil supply holes and before the steel balls are pressed in, the center holes bored from both ends of the shaft are in communication with each other. Accordingly, removal of the burrs present in the center holes can be performed easily and sufficiently, and inconveniences such that the burrs are separated during the use of the power unit to flow out into the oil pressure system with the result of producing a clogging of an orifice or the like can be obviated. 
   In addition, in the present embodiment, the high-pressure working oil flowing toward the clutch  44  on the main shaft  8  is supplied by being fed from the side of the front crankcase cover  24  to the front portion center hole  57  through the working oil supply pipe  59 . The low-pressure lubricating oil flowing toward the needle bearing  43 , which bears the first gear position driving gear  40 , is supplied from the side of the rear portion center hole  58 . The high-pressure working oil supplied towards the second and third gear position oil hydraulic type multiple disk clutches  65  and  66  on the counter shaft  9  is supplied from the side of the front crankcase cover  24  through the double-wall pipe  81  and by way of the front portion center hole  79 . The low-pressure lubricating oil flowing towards the needle bearing  63  for the second gear position driven gear  61  is supplied from the side of the front crankcase  25  through the oil passage between the front portion counter shaft  9   a  and the outer pipe  81   a . The low-pressure lubricating oil supplied towards the needle bearing  64  for the third gear position driven gear  62  is supplied from the side of the rear crankcase cover  27  through the rear portion center hole  80 . In the present embodiment, the steel ball is pressed into the narrowest portion of the center hole in each rotary shaft to partition the center hole into the front portion center hole and the rear portion center hole, thereby separating the oils that are different in pressure from each other and utilizing the center holes as passages for supplying the oils. Therefore, the oils can be supplied effectively with a simple structure. 
   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.