Patent Publication Number: US-7913492-B2

Title: Hydrostatic continuously variable transmission

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2007-095034 filed on Mar. 30, 2007 the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hydrostatic continuously variable transmission configured by connecting a hydraulic pump and a hydraulic motor via a hydraulic closed circuit and configured to enable variably controlling of the capacity of at least either of the hydraulic pump or the hydraulic motor, shifting the input revolution speed of the hydraulic pump and acquiring the output revolution speed of the hydraulic motor. 
     2. Description of Background Art 
     Various configurations of a hydrostatic continuously variable transmission are known. For example, hydrostatic continuously variable transmissions have been proposed and disclosed in JP-A No. H6-42446; JP Patent No. 2920772; JP-A No. H9-100909 and JP-A No. 2005-256979 by the applicants. These hydrostatic continuously variable transmissions disclosed in these patents and applications are each provided with a swash plate type plunger pump, a swash plate type plunger motor and a hydraulic closed circuit that connects a discharge port and a suction port of the swash plate type plunger pump to a suction port and a discharge port of the swash plate type plunger motor. The hydrostatic continuously variable transmission is configured so that a pump swash plate is driven by an engine, a pump cylinder and a motor cylinder are connected and are arranged on an output shaft, the rotation of a motor swash plate is regulated, and an angle of the motor swash plate can be variably adjusted. 
     A hydrostatic continuously variable transmission configured as described above is known. A clutch valve is provided that connects and cuts off an oil passage on the high pressure side and an oil passage on the low pressure side respectively forming the hydraulic closed circuit. A quantity in which a rotational driving force from the hydraulic pump is transmitted to the hydraulic motor is controlled. A clutch control for cutting off the rotational transmission is executed. For example, in JP-A No. 2005-256979, an automatic clutch using such a clutch valve is disclosed. This clutch valve is provided with a valve spool movably arranged in a spool hole axially extending in the supporting shaft that rotatably supports the hydraulic pump and the hydraulic motor, and connects and cuts off the oil passage on the high pressure side and the oil passage on the low pressure side by axially moving the valve spool. The clutch valve is provided with a spring (energizing means) that energizes the valve spool in a direction of disengagement and a centrifugal governor that generates a force corresponding to input revolution speed. The clutch valve is opened and closed according to a balance among the energizing force by the spring, a governor force and a load depending upon internal pressure (high pressure), and executes control for connecting and cutting off the oil passage on the high pressure side and the oil passage on the low pressure side. 
     In the above-mentioned clutch valve, the valve spool requires a part that receives an energizing force by the spring and governor force, a part that guides to enable an axial smooth movement in the spool hole and a part that connects and cuts off the oil passage on the high pressure side and the oil passage on the low pressure side according to the axial movement. Thus, the valve spool is formed in an axially long shape. In this case, as high precision is required for the peripheral dimension of a guide part fitted into a guide hole formed in the supporting shaft and guided to be axially moved in the spool hole and the peripheral dimension of a valve part fitted to a part in which the oil passage on the high pressure side and the oil passage on the low pressure side are open in the spool hole for connecting and cutting off the oil passage on the high pressure side and the oil passage on the low pressure side according to the axial movement, the above-mentioned clutch valve has a problem in that the manufacture of the valve spool is difficult and a great deal of manufacturing cost is required. Further, a problem exists wherein the precision is not met. Thus, the operation performance may be deteriorated. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The invention is made in view of such problems. It is an object of an embodiment of the present invention to provide a hydrostatic continuously variable transmission where the manufacture of a valve spool forming a clutch valve is simple and the manufacturing cost can be reduced. 
     The hydrostatic continuously variable transmission according to an embodiment of the present invention is configured by connecting a hydraulic pump and a hydraulic motor via a hydraulic closed circuit wherein the capacity of at least either of the hydraulic pump or the hydraulic motor is variably controlled. The input revolution speed of the hydraulic pump is shifted and the output revolution speed of the hydraulic motor is acquired. The hydrostatic continuously variable transmission according to an embodiment of the present invention is provided with the valve spool movably arranged in a spool hole axially extending in a supporting shaft that rotatably supports the hydraulic pump and the hydraulic motor. A clutch oil passage on the high pressure side is connected to an oil passage on the high pressure side forming the hydraulic closed circuit and is open to the spool hole. A clutch oil passage on the low pressure side is connected to an oil passage on the low pressure side forming the hydraulic closed circuit and is open to the spool hole. The valve spool is provided with a guide part fitted into a guide hole formed in the supporting shaft and guided so that the guide part is axially moved in the spool hole with a valve part fitted to a part in which the clutch oil passage on the high pressure side and the clutch oil passage on the low pressure side in the spool hole are open for connecting and cutting off the clutch oil passage on the high pressure side and the clutch oil passage on the low pressure side according to the axial movement. Further, the valve spool is formed by coupling a first spool member provided with a part in which the guide part is formed and a second spool member provided with a part in which the valve part is formed. 
     It is desirable that the first spool member and the second spool member coaxially extend and are mutually rockably coupled by a coupling pin extending in a direction perpendicular to the axis. 
     It is desirable that in the hydrostatic continuously variable transmission, a high dimensional precision is required for two or less peripheral parts of the first spool member to fit the peripheral parts to the guide hole in the first spool member. A high dimensional precision is required for two or less peripheral parts of the second spool member to fit the peripheral parts to the spool hole in the second spool member. 
     According to the hydrostatic continuously variable transmission configured as described above according to an embodiment of the present invention, as the valve spool is formed by coupling the first spool member is provided with the part in which the guide part is formed and the second spool member is provided with the part in which the valve part is formed, the valve spool is formed only by coupling the first and second spool members after they are separately manufactured. Therefore, the manufacture is facilitated, the manufacturing cost can be reduced, and dimensional precision can be enhanced. More specifically, as it is for only the guide part in the first spool member that high dimensional precision is required, the manufacture is simple and as it is also for only the valve part in the second spool member that high dimensional precision is required, the manufacture is simple. 
     When the first and second spool members coaxially extend and are mutually rockably coupled by a coupling pin extended in a direction perpendicular to the axis, their coupled structure is simple. 
     When a high dimensional precision is required for respective two or less peripheral parts in the first and second spool members, the high dimensional precision is secured. In addition, the manufacture can be facilitated. 
     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 sectional view showing the configuration of a hydrostatic continuously variable transmission according to the invention; 
         FIG. 2  is an outside drawing showing a motorcycle provided with the hydrostatic continuously variable transmission; 
         FIG. 3  is a schematic drawing showing the power transmission path configuration of a power unit provided with the hydrostatic continuously variable transmission; 
         FIG. 4  is a sectional view showing the configuration of the hydrostatic continuously variable transmission; 
         FIG. 5  is a sectional view enlarged to show the configuration of a part of the hydrostatic continuously variable transmission; 
         FIG. 6  is a sectional view enlarged to show the configuration of the part of the hydrostatic continuously variable transmission. 
         FIG. 7  is a front view and a sectional view showing a cotter used for positioning a rotor in the hydrostatic continuously variable transmission; 
         FIG. 8  is a front view and a sectional view showing a retainer ring used for positioning the rotor in the hydrostatic continuously variable transmission; 
         FIG. 9  is a front view and a sectional view showing a snap ring used for positioning the rotor in the hydrostatic continuously variable transmission; 
         FIG. 10  is a sectional view showing a motor servo mechanism in the hydrostatic continuously variable transmission; 
         FIG. 11  is a sectional view showing the structure of a hydraulic pump and a clutch in the hydrostatic continuously variable transmission; 
         FIG. 12  is a sectional view showing the structure of a transmission output shaft and the output rotor in the hydrostatic continuously variable transmission; 
         FIG. 13  is a sectional view showing the structure of the transmission output shaft and the output rotor in the hydrostatic continuously variable transmission; 
         FIG. 14  is a sectional view showing the structure of the transmission output shaft and the output rotor in the hydrostatic continuously variable transmission; 
         FIG. 15  is a sectional view showing the structure of a lock-up mechanism in the hydrostatic continuously variable transmission; 
         FIG. 16  is a sectional view showing the structure when the lock-up mechanism is located in a normal position in a condition viewed along a line Y-Y shown in  FIG. 15 ; 
         FIG. 17  is a sectional view showing the structure when the lock-up mechanism is located in a lock-up position in a condition viewed along the line Y-Y shown in  FIG. 15 ; 
         FIG. 18  is a hydraulic circuit diagram showing the oil passage configuration of the hydrostatic continuously variable transmission; 
         FIG. 19(   a ) is a partial sectional view showing the configuration of a valve spool forming the clutch of the hydrostatic continuously variable transmission,  FIGS. 19(   b ) and  19 ( c ) are view showing the retaining ring; and 
         FIG. 20  is a sectional view showing the configuration of the circumference of a motor swash plate in a condition close to the gear ratio of 1.0 in the hydrostatic continuously variable transmission. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, a preferred embodiment of the invention will be described below.  FIG. 2  illustrates the whole appearance of a motorcycle that is provided with a hydrostatic continuously variable transmission according to the invention.  FIG. 2  shows a condition in which a side cover of the motorcycle is partially removed and its internal structure is exposed. This motorcycle  100  is provided with a main frame  110 , a front fork  120  turnably attached to a front end of the main frame  110  with a diagonally vertically extended axis in the center, a front wheel  101  rotatably attached to a lower end of the front fork  120 , a swing arm  130  vertically rockably fastened to the rear of the main frame  110  with a horizontally extended fastening shaft  130   a  in the center and a rear wheel  102  rotatably attached to a rear end of the swing arm  130 . 
     A fuel tank  111  is provided together with a seat  112  for an occupant to sit, a main stand  113   a  and a substand  113   b . A headlight  114  is provided that radiates light ahead during night driving. In addition, a radiator  115  is provided for cooling engine cooling water, a power unit PU is provided for generating rotational driving force for driving the rear wheel  102  and other parts are attached to the main frame  110 . A handlebar (a steering handlebar)  121  is provided for the occupant to operate so as to steer the motorcycle, a rear view mirror  122  is provided for acquiring a back field of view and other parts are attached to the front fork  120 . A drive shaft for transmitting the rotational driving force generated by the power unit PU to the rear wheel is provided in the swing arm  130  as described later. 
     In the motorcycle  100  configured as described above, the hydrostatic continuously variable transmission CVT is used for the power unit PU and the power unit PU will be described below. First,  FIG. 3  shows the schematic configuration of the power unit PU and the power unit PU is provided with an engine E that generates rotational driving force, the hydrostatic continuously variable transmission CVT that continuously shifts output rotation and a transmission gear train GT that switches a rotational direction output from the hydrostatic continuously variable transmission CVT and transmits the output rotation. 
     As shown in  FIG. 2 , the engine E is a V-type engine provided with a V-type bank with cylinders  1  that extend diagonally upwardly in a longitudinal direction in a V type. The engine E is configured by arranging a piston  2  in each cylinder  1  provided with intake and exhaust valves  1   a ,  1   b  in each head. In the engine E, the intake valve  1   a  and the exhaust valve  1   b  are opened and closed at predetermined times, air-fuel mixture is combusted in the cylinder chamber for reciprocating the piston  2 , the reciprocation of the piston  2  is transmitted to a crankcase  3   a  via a connecting rod  2   a , and a crankshaft  3  is rotated. An input driving gear  4  provided with a damper  4   a  is attached to an end of the crankshaft  3  and the rotational driving force of the crankshaft  3  is transmitted to the input driving gear  4 . 
     A driving sprocket  8   a  is attached to the crankshaft  3  and transmits the rotational driving force to a driven sprocket  8   c  attached to pump driving shafts  9   a ,  9   b  via a chain  8   b . An oil pump OP and a water pump WP are arranged on the pump driving shafts  9   a ,  9   b  as shown in  FIG. 3  and are driven by the engine E. Hydraulic fluid discharged from the oil pump OP is supplied as replenishment oil and lubricating oil of the hydrostatic continuously variable transmission CVT as described later. As shown in  FIG. 2 , the hydraulic fluid is cooled by an oil cooler  116  arranged in a rear lower part of the power unit PU, and is filtered by an oil filter  117 . Cooling water discharged from the water pump WP is used for cooling the engine E, however, the cooling water the temperature of which rises because of the engine E is cooled by the radiator  115 . 
     The hydrostatic continuously variable transmission CVT is also provided with a swash plate type plunger hydraulic pump P and a swash plate type plunger hydraulic motor M. An input driven gear  5  connected to a pump casing that forms the swash plate type plunger hydraulic pump P and is engaged with the input driving gear  4 . The rotational driving force of the engine E is transmitted to the input driven gear  5 , and the pump casing is rotated. The hydraulic pump P is a fixed capacity type with an angle of a swash plate of which that is fixed. The hydraulic motor M is a variable capacity type with an angle of a swash plate that is variable. The hydraulic motor is provided with a motor servomechanism SV for variably adjusting the angle of the swash plate. Though the details of the hydrostatic continuously variable transmission CVT are described later, the output rotation variably shifted by the hydrostatic continuously variable transmission CVT is output to a transmission output shaft  6 . 
     The transmission gear train GT is connected to the transmission output shaft  6 , and switching between a forward motion and neutral, deceleration and others are applied to the rotation of the supporting shaft or transmission output shaft  6  by the transmission gear train GT. The transmission gear train GT is provided with a counter shaft  10  and a first output driving shaft  15  respectively extending in parallel with the transmission output shaft  6 . The transmission gear train GT is also provided with a first gear  11  connected to the transmission output shaft  6 , a second gear  12  arranged so that the second gear can be axially slid on the counter shaft  10  and is rotated integrally with the counter shaft  10 , a third gear  13  connected to the counter shaft  10  and a fourth gear  14  ordinarily engaged with the third gear  13  and connected to the first output driving shaft  15 . The second gear  12  is axially slid on the counter shaft  10  according to the operation for a change by the rider, is engaged with the first gear  11  to be a forward motion, and is also separated from the first gear  11  to be neutral. 
     An output driving bevel gear  15   a  is attached to an end of the first output driving shaft  15  and the rotational driving force is transmitted from an output driven bevel gear  16   a  engaged with the output driving bevel gear  15   a  to a second output driving shaft  16 . The second output driving shaft  16  is connected to the drive shaft  18  via a universal joint  17 . The drive shaft  18  is connected to the rear wheel  102  through the inside of the swing arm  130  as described above with the rotational driving force being transmitted to the rear wheel  102  for driving the rear wheel. The universal joint  18  is located coaxially with the fastening shaft  130   a  for fastening the swing arm  130  to the main frame  110 . 
     Referring to  FIGS. 1 and 4  to  6 , the hydrostatic continuously variable transmission CVT will be described. The hydrostatic continuously variable transmission CVT is provided with the swash plate type plunger hydraulic pump P and the swash plate type plunger hydraulic motor M and the transmission output shaft  6  extends with the output shaft piercing its center. The transmission output shaft  6  is rotatably supported by a transmission housing IISG via ball bearings  7   a ,  7   b ,  7   c.    
     The hydraulic pump P is configured by the pump casing  20  arranged on the transmission output shaft  6  coaxially and relatively rotatably with the transmission output shaft  6 . A pump swash plate  21  is arranged inside the pump casing  20  with the pump swash plate tilted by a predetermined angle with a rotational central axis of the pump casing  20 . A pump cylinder  22  is arranged opposite to the pump swash plate  21  with plural pump plungers  23  slidably arranged in each pump plunger hole  22   a  axially extending in an annular arrangement encircling a central axis of the pump cylinder in the pump cylinder  22 . The pump casing  20  is rotatably supported by bearings  7   b  and  22   c  on the transmission output shaft  6  and on the pump cylinder  22  and is rotatably supported by the bearing  7   a  on the transmission housing HSG. The pump swash plate  21  is rotatably arranged with its axis tilted by bearings  21   a ,  21   b  by a predetermined angle with the pump casing  20  in the center. More specifically, the pump cylinder  22  is supported by the bearing  22   c  coaxially and relatively rotatably with the pump casing  20 . 
     The input driven gear  5  is fastened to the periphery of the pump casing  20  by a bolt  5   a . An outer end of the pump plunger  23  projects outwardly, is touched and fitted to a swash surface  21   a  of the pump swash plate  21 , and its inner end located in the pump plunger hole  22   a  forms a pump oil chamber  23   a  in the pump plunger hole  22   a  opposite to a valve body  51  of a distributing valve  50  described later. A pump opening  22   b  that acts as a pump discharge port and a pump inlet is formed at the end of the pump plunger hole  22   a . When the input driven gear  5  is driven as described above, the pump casing  20  is rotated, the pump swash plate  21  arranged inside the pump casing is rocked by the rotation of the pump casing  20 , the pump plunger  23  is reciprocated in the pump plunger hole  22   a  according to the rocking of the swash plate surface  21   a , and hydraulic fluid inside the pump oil chamber  23   a  is discharged and is sucked. 
     A pump eccentric member  20   a  is connected to a right end in the drawings of the pump casing  20  by a bolt  5   b . An inside face  20   b  of the pump eccentric member  20   a  is formed in the shape of a cylinder eccentric with a rotational axis of the pump casing  20 . The pump eccentric member  20   a  is provided with the inside face  20   b  eccentric as described above and is formed separately from the pump casing  20 . Thus, the assembly is simple to manufacture. 
     The hydraulic motor M is configured by a motor casing  30  (formed by plural casings  30   a ,  30   b ) connected, fixed and held to/by the transmission housing HSG. A motor rocking member  35  is slidably supported by a supporting cylindrical surface  30   c  formed on an inside face of the motor casing  30  (the casing  30   b ) and is rockably supported with the center O of the rocking that extends in a direction (a direction perpendicular to a paper face) of a right angle with a central axis of the transmission output shaft  6  in the center. A motor swash plate  31  is rotatably supported by bearings  31   a ,  31   b  inside the motor rocking member  35  with a motor cylinder  32  being opposite to the motor swash plate  31 . A plurality of motor plungers  33  are slidably arranged in each motor plunger hole  32   a  axially pierced in an annular arrangement encircling a central axis of the motor cylinder in the motor cylinder  32 . The motor cylinder  32  is rotatably supported by the motor casing  30  via a bearing  32   c  on the periphery of the motor cylinder. 
     In the hydraulic motor M, a lock-up mechanism  90  (see  FIGS. 15 to 17 ) is provided to a left end in the drawings of the motor casing  30  and a motor eccentric member  91  forming the lock-up mechanism  90  is slidably touched to an end of the motor casing  30 . The lock-up mechanism  90  will be described later, however, it is rocked between a lock-up position in which a cylindrical inside face  91   a  formed on the motor eccentric member  91  is located coaxially with the motor cylinder  32  and a normal position in which the cylindrical inside face is located in an eccentric position with a rotational axis of the motor cylinder  32 . 
     An outer end of the motor plunger  33  projects outwardly and is touched to a face  31   a  of the motor swash plate  31 . An inner end located in the plunger hole  32   a  is opposite to the valve body  51 , and forms a motor oil chamber  33   a  in the motor plunger hole  32   a . A motor opening  32   b , that acts as a motor discharge port and a motor inlet, is formed at the end of the motor plunger hole  32   a . An arm part  35   a  formed by protruding an end of the motor rocking member  35  on the side of an outside diameter projects outwardly in a radial direction and is coupled to the motor servomechanism SV. Control for moving the arm part  35   a  laterally in  FIG. 1  and others is executed by the motor servomechanism SV and control for rocking the motor rocking member  35  with the center O of rocking in the center is executed. When the motor rocking member  35  is rocked as described above, the motor swash plate  31  rotatably supported inside the motor rocking member is also rocked together, and an angle of the swash plate varies. 
     The distributing valve  50  is arranged between the pump cylinder  22  and the motor cylinder  32 .  FIGS. 5 and 6  show the part with the part enlarged, the valve body  51  of the distributing valve  50  is held between the pump cylinder  22  and the motor cylinder  32 , is integrated with them by brazing, and the motor cylinder  32  is connected to the transmission output shaft  6  via a spline. Therefore, the pump cylinder  22 , the distributing valve  50 , the motor cylinder  32  and the transmission output shaft  6  are integrally rotated. 
     The pump cylinder  22 , the distributing valve  50  (its valve body  51 ) and the motor cylinder  32  respectively integrated as described above are called an output rotor and are configuration for positioning and attaching the output rotor in an axial predetermined position on the transmission output shaft  6  will be described below. A regulating part  6   f  projecting in the shape of a flange on the peripheral side of the transmission output shaft  6  is formed for the positioning, a left end face of the pump cylinder  22  is touched to the regulating part  6   f , and to the left positioning is performed. In the meantime, the to the right positioning of the output rotor is performed by a fitting member  80  attached to the transmission output shaft  6  opposite to a right end face of the motor cylinder  32 . 
     As shown in  FIGS. 12 to 14  in detail, a first fitting groove  6   g  and a second fitting groove  6   h  respectively annular are formed on the transmission output shaft  6  so as to attach the fitting member  80 . Inside faces  81   a  of a pair of cotters  81  formed by dividing in a semicircle as shown in  FIG. 7  are fitted into the first fitting groove  6   g . A retainer ring  82  shown in  FIG. 8  is attached on the cotters, a side plate  82   b  of the retainer ring  82  is touched to the sides of the cotters  81 , a peripheral plate  82   a  covers outside faces  81   b  of the cotters  81 , and the retainer ring holds the cotters  81  in this condition. Further, a snap ring  83  shown in  FIG. 9  is fitted into the second fitting groove  6   h  and holds the retainer ring  82  in this condition. As a result, the right end face of the motor cylinder  32  is touched to the fitting member  80  and right positioning is performed. As known from the above-mentioned configuration, the output rotor is positioned on the transmission output shaft  6  between the regulating part  6   f  and the fitting member  80 . 
     The distributing valve  50  will be described as illustrated in  FIGS. 5 and 6 . A plurality of pump-side spool holes  51   a  and a plurality of motor-side spool holes  51   b  respectively extend in a radial direction and are formed at an equal interval in a circumferential direction are formed in two rows in the valve body  51  forming the distributing valve  50 . A pump-side spool  53  is slidably arranged in the pump-side spool hole  51   a  and a motor-side spool  55  is slidably arranged in the motor-side spool hole  51   b.    
     The pump-side spool hole  51   a  is formed corresponding to the pump plunger hole  22   a  and the plurality of pump-side communicating passages  51   c  each of which connects the corresponding pump opening  22   b  (the corresponding pump oil chamber  23   a ) and the corresponding pump-side spool hole  51   a  are formed in the valve body  51 . The motor-side spool hole  51   b  is formed corresponding to the motor plunger hole  32   a  and the plurality of motor-side communicating passages  51   d  each of which connects the corresponding motor opening  32   b  (the corresponding motor oil chamber  33   a ) and the corresponding motor-side spool hole  51   b  are formed in the valve body  51 . 
     In the distributing valve  50 , a pump-side cam ring  52  is further arranged in a position encircling a peripheral end of the pump-side spool  52  and a motor-side cam ring  54  is further arranged in a position encircling a peripheral end of the motor-side spool  55 . The pump-side cam ring  52  is attached to the inside face  20   b  made eccentric from the rotational central axis of the pump casing  20  on the inner surface of the pump eccentric member  20   a  connected to an end of the pump casing  20  by the bolt  5   b  and is rotatably supported by the pump casing  20 . The motor-side cam ring  54  is attached on an inside face  91   a  of a motor eccentric member  91  slidably located at the end of the motor casing  30 . A peripheral end of the pump-side spool  53  is relatively rotatably fitted to an inside face of the pump-side cam ring  52  and a peripheral end of the motor-side spool  55  is relatively rotatably fitted to an inside face of the motor-side cam ring  54 . 
     An inside passage  56  is formed between an inside face of the valve body  51  and the periphery of the transmission output shaft  6  and inside ends of the pump-side spool hole  51   a  and the motor-side spool hole  51   b  communicate with the inside passage  56 . In addition, an outside passage  57  that connects the pump-side spool hole  51   a  and the motor-side spool hole  51   b  is formed in the valve body  51 . 
     The action of the distributing valve  50  configured as described above will be described. When the driving force of the engine E is transmitted to the input driven gear  5  and the pump casing  20  is rotated, the pump swash plate  21  is rocked according to the rotation. Therefore, the pump plunger  23  touched and fitted to the swash surface  21   a  of the pump swash plate  21  is axially reciprocated in the pump plunger hole  22   a  by the rocking of the pump swash plate  21 , hydraulic fluid is discharged from the pump oil chamber  23   a  via the pump opening  22   b  according to the inside movement of the pump plunger  23 , and is sucked in the pump oil chamber  23   a  through the pump opening  22   b  according to the outside movement. 
     At this time, the pump-side cam ring  52  attached to the inside face  20   b  of the pump eccentric member  20   a  connected to the end of the pump casing  20  is rotated together with the pump casing  20 . However, as the pump-side cam ring  52  is attached with the pump-side cam ring eccentric with the rotational center of the pump casing  20 , the pump-side spool  53  is reciprocated in the radial direction in the pump-side spool hole  51   a  according to the rotation of the pump-side cam ring  52 . When the pump-side spool  53  is reciprocated and is moved on the side of an inside diameter from a condition shown in  FIGS. 5 and 6  as described above, the pump-side communicating passage  51   c  and the outside passage  57  communicate via a spool groove  53   a . When the pump-side spool  53  is moved on the side of an outside diameter from the condition shown in  FIGS. 5 and 6 , the pump-side communicating passage  51   c  and the inside passage  56  communicate. 
     While the swash plate  21  is rocked according to the rotation of the pump casing  20  and the pump plunger  23  is reciprocated between a position (called a bottom dead center) in which the pump plunger is pushed on the outermost side and a position (called a top dead center) in which the pump plunger is pushed on the innermost side, the pump-side cam ring  52  reciprocates the pump-side spool  53  in the radial direction. As a result, when the pump plunger  23  is moved from the bottom dead center to the top dead center according to the rotation of the pump casing  20  and the hydraulic fluid in the pump oil chamber  23   a  is discharged via the pump opening  22   b , the hydraulic fluid is delivered into the outside passage  57  through the pump-side communicating passage  51   c . In the meantime, when the pump plunger  23  is moved from the top dead center to the bottom dead center according to the rotation of the pump casing  20 , hydraulic fluid in the inside passage  56  is sucked in the pump oil chamber  23   a  through the pump-side communicating passage  51   c  and the pump opening  22   b . As known from this, when the pump casing  20  is rotated, hydraulic fluid discharged from the hydraulic pump P is supplied to the outside passage  57  and the hydraulic fluid is sucked in the hydraulic pump P from the inside passage  56 . 
     In the meantime, as the motor-side cam ring  54  attached on the inside face  91   a  of the motor eccentric member  91  slidably located at the end of the motor casing  30  is eccentric with the rotational center of the motor cylinder  32  (the output rotor and the transmission output shaft  6 ) when the motor eccentric member  91  is located in a normal position, the motor-side spool  55  is reciprocated in the radial direction in the motor-side spool hole  51   b  according to the rotation of the motor cylinder  32 . When the motor-side spool  55  is reciprocated as described above and is moved on the side of the inside diameter from the condition shown in  FIGS. 5 and 6 , the motor-side communicating passage  51   d  and the outside passage  57  communicate via a spool groove  55   a . When the motor-side spool  55  is moved on the side of the outside diameter from the condition shown in  FIGS. 5 and 6 , the motor-side communicating passage  51   d  and the inside passage  56  communicate. A situation wherein the motor eccentric member  91  is located in a lock-up position will be described later and the situation wherein the motor eccentric member is located in the normal position is described above. 
     As described above, hydraulic fluid discharged from the hydraulic pump P is delivered into the outside passage  57 , is supplied to the motor oil chamber  33   a  from the motor-side communicating passage  51   d  via the motor opening  32   b , and the motor plunger  33  is thrusted axially outward. As described above, the motor plunger is configured so that an outside end of the motor plunger  33  to which the axial outward pressure is applied is slid from the top dead center to the bottom dead center on the motor swash plate  31  in a condition shown in  FIG. 1  in which the motor rocking member  35  is rocked, and the motor cylinder  32  is rotated so that the motor plunger  33  is moved from the top dead center to the bottom dead center along the motor swash plate  31  by the axial outward thrust. 
     To enable such rotation, while the motor plunger  33  is reciprocated between the position in which the motor plunger is pushed on the outermost side (the bottom dead center) and the position in which the motor plunger is pushed on the innermost side (the top dead center) according to the rotation of the motor cylinder  32 , the motor-side cam ring  54  reciprocates the motor-side spool  55  in the radial direction. When the motor cylinder  32  is rotated as described above, the motor plunger  33  is pushed and moved from the bottom dead center to the top dead center, that is, inward along the motor swash plate  31  according to the rotation and hydraulic fluid in the motor oil chamber  33   a  is delivered into the inside passage  56  from the motor opening  32   b  via the motor-side communicating passage  51   d . The hydraulic fluid delivered into the inside passage  56  as described above is sucked in the pump oil chamber  23   a  through the pump-side communicating passage  51   c  and the pump opening  22   b  as described above. 
     As set forth in the above-mentioned description, when the pump casing  20  is rotated by the rotational driving force of the engine E, hydraulic fluid is discharged into the outside passage  57  from the hydraulic pump P, is delivered into the hydraulic motor M, and rotates the motor cylinder  32 . The hydraulic fluid that rotates the motor cylinder  32  is delivered into the inside passage  56  and is sucked in the hydraulic pump P from the inside passage  56 . As described above, a hydraulic closed circuit connecting the hydraulic pump P and the hydraulic motor M is formed by the distributing valve  50 , hydraulic fluid discharged from the hydraulic pump P according to the rotation of the hydraulic pump P is delivered into the hydraulic motor M via the hydraulic closed circuit, the hydraulic motor is rotated, and further, the hydraulic fluid that drives the hydraulic motor M and is discharged is returned to the hydraulic pump P via the hydraulic closed circuit. 
     In this case, when the hydraulic pump P is driven by the engine E, the rotational driving force of the hydraulic motor M is transmitted to the wheels and the vehicle drives, the outside passage  57  is an oil passage on the high pressure side and the inside passage  56  is an oil passage on the low pressure side. In the meantime, when the driving force of the wheel is transmitted to the hydraulic motor M, the rotational driving force of the hydraulic pump P is transmitted to the engine E and engine brake action is produced as in driving on a descending slope, the inside passage  56  is turned an oil passage on the high pressure side and the outside passage  57  is turned an oil passage on the low pressure side. At this time, as the pump cylinder  22  and the motor cylinder are connected to the transmission output shaft  6  and are integrally rotated, the pump cylinder  22  is also rotated together as described above when the motor cylinder  32  is rotated and relative revolution speed between the pump casing  20  and the pump cylinder  22  is reduced. Therefore, the relation between the revolution speed Ni of the pump casing  20  and the revolution speed No of the transmission output shaft  6  (that is, the revolution speed of the pump cylinder  22  and the motor cylinder  32 ) is as shown in the following expression (1) in relation to pump capacity Vp and motor capacity Vm. 
     (Mathematical Expression 1)
 
 Vp· ( Ni−No )= Vm·No   (1)
 
     The motor capacity Vm can be continuously varied by control that the motor rocking member  35  is rocked according to the motor servomechanism SV. That is, when the revolution speed Ni of the pump swash plate  21  is fixed in the expression (1), the revolution speed of the transmission output shaft  6  continuously shifts in control that the motor capacity Vm is continuously varied and as known from this, shift control is executed by rocking the motor rocking member  35  and varying the motor capacity Vm by the motor servomechanism SV. 
     In a control wherein an oscillation angle of the motor rocking member  35  is reduced, the motor capacity Vm decreases. When the pump capacity Vp is fixed and the revolution speed Ni of the pump swash plate  21  is fixed in the relation shown in the expression (1), control that the revolution speed of the transmission output shaft  6  is increased so that the revolution speed approaches the revolution speed Ni of the pump swash plate  21 , that is, continuous shift control to top speed is executed. When an angle of the motor swash plate is zero, that is, when the motor swash plate is upright, the transmission gear ratio is theoretically the top gear ratio (Ni=No) to be in a condition wherein the oil pressure is locked, the pump casing  20  is rotated integrally with the pump cylinder  22 , the motor cylinder  32  and the transmission output shaft  6 , and mechanical power transmission is performed. 
     As described above, the control wherein the motor capacity is continuously varied is executed by rocking the motor rocking member  35  and variably controlling the angle of the motor swash plate. Mainly referring to  FIG. 10 , the motor servomechanism SV for rocking the motor rocking member  35  as described above will be described below. 
     The motor servomechanism SV is provided with a ball screw shaft  41  located in the vicinity of the arm part  35   a  of the motor rocking member  35 , extending in parallel with the transmission output shaft  6  and rotatably supported by the transmission housing HSG via bearings  40   a ,  40   b  and a ball nut  40  screwed on a male screw  41   a  formed on the periphery of the ball screw shaft  41 . A ball female screw is formed by multiple balls held in the shape of a screw according to a gauge on the inside face of the ball nut  40  and is screwed on the male screw  41   a . The ball nut  40  is coupled to the arm part  35   a  of the motor rocking member  35 , when the ball screw shaft  41  is rotated, the ball nut  40  is moved laterally on the ball screw shaft  41 , and the motor rocking member  35  is rocked. 
     A swash plate control motor (an electric motor)  47  is attached on the outside face of the transmission housing HSG to rotate the ball screw shaft  41  as described above. An idle shaft  43  is provided in parallel with a driving shaft  46  of the swash plate control motor  47  and an idle gear member provided with gears  44  and  45  is rotatably attached on the idle shaft  43 . A gear  46   a  is formed at the end of the driving shaft  46  of the swash plate control motor  47  and is engaged with the gear  45 . In the meantime, a gear  42  is connected to a shaft part  41   b  formed by protruding a left part of the ball screw shaft  41  to the left and is engaged with the gear  44 . 
     Therefore, when the driving shaft  46  is rotated with the rotation of the swash plate control motor  47  controlled, the rotation is transmitted to the gear  45 , is transmitted from the gear  44  integrally rotated with the gear  45  to the gear  42 , and the ball screw shaft  41  is rotated. The ball nut  40  is moved laterally on the shaft  41  according to the rotation of the ball screw shaft  41  and control for rocking the motor rocking member  35  is executed. As the rotation of the swash plate control motor  47  is transmitted to the ball screw shaft  41  via the gears  46   a ,  45 ,  44 ,  42  as described above, the transmission ratio can be freely varied by suitably setting the gear ratio of these gears. 
     The swash plate control motor  47  is arranged with the swatch control motor  47  being exposed outside in the vicinity of the rear side of the base of the rear cylinder  1  in the V-type engine E as shown in  FIG. 2 . The cylinder  1  is integrated with the transmission housing HSG and the swash plate control motor  47  is arranged in a space between the rear cylinder  1  and the transmission housing HSG. As the space can be effectively utilized by arranging the swash plate control motor  47  in the space between the rear cylinder  1  and the transmission housing HSG as described above and the swash plate control motor is located apart from the fastening shaft  130   a  of the swing arm  130  shown in  FIG. 2 , no limitation for avoiding interference with the swing arm  130  is applied to the shape of the swing arm. In addition, the swash plate control motor  47  can be protected from a splash from the downside of the body during driving from rainwater in a front direction and from dust. Further, the swash plate control motor  47  is arranged with the swatch control motor  47  being biased on the left side from the center in a lateral direction of the body as shown in  FIG. 10  and is effectively cooled by efficiently hitting an air flow from the front direction in driving on the swash plate control motor  47 . 
     In the hydrostatic continuously variable transmission CVT configured as described above, when the inside passage  56  and the outside passage  57  communicate, no high pressure oil is generated and power transmission between the hydraulic pump P and the hydraulic motor M can be cut off. More specifically, clutch control is enabled by a communication angle control between the inside passage  56  and the outside passage  57 . A clutch CL for the clutch control is provided to the hydrostatic continuously variable transmission CVT. As illustrated in  FIGS. 11 to 14 , the clutch CL will be described below. 
     The clutch CL is configured by a rotor  60  connected to the end of the pump casing  20  by a bolt  60   b , weights  61  (balls or rollers) received in plural receiving grooves  60   a  diagonally extend in the radial direction on an inside face of the rotor  60 , a disc like pressure receptor  62  is provided with an arm part  62   a  opposite to the receiving groove  60   a . A spring  63  presses the pressure receptor  62  so that the arm part  62   a  presses the weight  61  in the receiving groove  60   a  and a valve spool  70  is fitted to a fitting part  62   e  on one end side of the pressure receptor  62 . 
     A through hole  60   e  having a rotational central axis in the center is formed in the rotor  60 , a cylindrical part  62   b  of the pressure receptor  62  is movably inserted into the through hole  60   c , and the pressure receptor  62  can be axially moved. Therefore, when the pump casing  20  is still and the rotor  60  is not rotated, the arm part  62   a  presses the weight  61  in the receiving groove  60   a  by energizing force applied to the pressure receptor  62  by the spring  63 . At this time, as the receiving groove  60   a  diagonally extends as shown in  FIG. 11 , the weight  61  is pushed inward in the radial direction and the pressure receptor  62  is moved to the left as shown in  FIGS. 1 and 11 . 
     When the pump casing  20  is rotated and the rotor  60  is rotated from this condition, the weight  61  is pushed outward in the radial direction in the receiving groove  60   a  by centrifugal force. When the weight  61  is pushed out in a direction of an outside diameter by centrifugal force as described above, the weight  61  is moved diagonally to the right along the receiving groove  60   a , pushes the arm part  62   a  to the right and the pressure receptor  62  is moved to the right against the pressure of the spring  63 . The quantity in which the pressure receptor  62  is moved to the right varies according to centrifugal force that acts on the weight  61 , that is, the revolution speed of the pump casing  20  and when the revolution speed is equal to or exceeds a predetermined revolution speed, the pressure receptor is moved to the right to a position shown in  FIG. 4 . The valve spool  70  fitted to the fitting part  62   c  of the pressure receptor  62  is moved axially laterally as described above and is fitted into a spool hole  6   d  open to an end of the transmission output shaft  6  and axially extends and is moved axially laterally together with the pressure receptor  62 . 
     A governor mechanism that generates an axial governor force corresponding to the input revolution speed of the hydraulic pump P using a centrifugal force that acts on the weight  61  by the rotation of the pump casing  20  is configured by the rotor  60 , the weight  61  and the pressure receptor  62 . 
     An inside branched oil passage  6   a  branched from the inside passage  56  and connected to the spool hole  6   d  and outside branched oil passages  6   b ,  6   c  connected from a communicating passage  57   a  branched from the outside passage  57  to the spool hole  6   d  are formed in the transmission output shaft  6  in which the spool hole  6   d  is formed as shown in  FIGS. 5 ,  6  and  11  to  14  in detail.  FIGS. 5 and 12  correspond to  FIG. 1  and show a condition wherein the pressure receptor  62  is moved to the left and the valve spool  70  is moved to the left, in this condition, the inside branched oil passage  6   a  and the outside branched oil passage  6   c  communicate via a right groove  72  of the valve spool  70 , and the inside passage  56  and the outside passage  57  communicate.  FIGS. 6 and 14  correspond to  FIG. 4  and show a condition wherein the pressure receptor  62  is moved to the right and the valve spool  70  is moved to the right, in this condition, the inside branched oil passage  6   a  and the outside branched oil passage  6   c  are cut off by a central land  73  of the valve spool  70 , and the inside passage  56  and the outside passage  57  are also cut off.  FIG. 13  shows a condition in which the valve spool  70  is located in an intermediate position. 
     As described above, as the valve spool  70  is moved to the left when the pump casing  20  is still, the inside branched oil passage  6   a  and the outside branched oil passage  6   c  communicate at this time and power transmission between the hydraulic pump P and the hydraulic motor M is cut off to be in a condition wherein the clutch is disengaged. When the pump casing  20  is driven from this condition, the pressure receptor  62  is gradually moved to the right by centrifugal force that acts on the weight  61  according to the number of revolutions and speed of the pump casing and the valve spool  70  is also moved to the right together. As a result the inside branched oil passage  6   a  and the outside branched oil passage  6   c  are gradually cut off by the central land  73  of the valve spool  70  and the clutch is gradually engaged. 
     In the hydrostatic continuously variable transmission CVT according to this embodiment, when the pump case  20  is rotated by the engine E, the valve spool  70  is moved to the left to be in the condition that the clutch is disengaged while engine speed is low (in idling) and as the engine speed rises, the clutch is gradually engaged. 
     An outside diameter d1 of the central land  73  in the valve spool  70  and an outside diameter d2 of a left land  74  are set so that d1&lt;d2. Therefore, when the valve spool  70  is moved to the right to be in the condition that the clutch is engaged, oil pressure in the outside passage  57  that acts in a left groove  75  of the valve spool  70  acts in a direction in which the valve spool  70  is moved to the left. The to the left thrust corresponds to the magnitude of the oil pressure that acts in the left groove  75  and the difference in the pressure received area depends upon the difference between the outside diameters d1, d2. The difference in the pressure received area is fixed, however, the oil pressure that acts in the left groove  75  is oil pressure in the outside passage  57 , varies according to the driving force, and the bigger the driving force is, the higher the oil pressure is. This configuration is equivalent to an oil pressure applying mechanism described in the scope of claims. 
     As known from this, clutch engagement control by the movement of the valve spool  70  is executed according to balance (Fgov=Fp+Fspg) among governor force (Fgov) generated by centrifugal force that acts on the weight  61  corresponding to the number of revolutions and speed of the pump casing  20 , energizing force (Fspg) by the spring  63  and thrust (Fp) depending upon the oil pressure that acts in the left groove  75  of the valve spool  70 . Control that the clutch is engaged as the rotation of the pump casing  20  increases is executed and control that force in a direction in which the clutch is disengaged is applied as the oil pressure of the outside passage  57  increases (as transmission driving force from the hydraulic pump P to the hydraulic motor M increases) is executed. 
       FIG. 13  shows a condition of an intermediate stage when clutch engagement control and clutch disengagement control are executed as described above, that is, a condition of a partial clutch engagement. In this condition, a right end  73   a  of the central land  73  of the valve spool  70  slightly communicates with the outside branched oil passage  6   b  to be in a condition wherein the inside passage  56  and the outside passage  57  partially communicate, that is, in the condition of partial clutch engagement. In the condition of partial clutch engagement, the inside passage  56  and the outside passage  57  communicate or are cut off by a slight axial movement of the valve spool  70 . However, as the axial movement of the valve spool  70  is balanced among the governor force (Fgov), the energizing force and the thrust depends upon the oil pressure as described above, the valve spool  70  is operated on the side on which the clutch is disengaged. When the thrust depends upon the oil pressure rapidly increases by rapid throttle operation, the inside passage  56  and the outside passage  57  repeat communication and cut off, and it is difficult to stably transmit power. 
     Therefore, to stabilize clutch performance by preventing the valve spool  70  from too sensitively reacting and being moved, a shock absorbing mechanism is provided and referring to  FIGS. 1 ,  4  and  11 , the shock absorbing mechanism will be described below. As shown in these drawings, a variable oil chamber forming groove  76  is provided on the left side of the left land  74  of the valve spool  70  and a guide land  71  having a smaller diameter than that of the left land  74  is provided to the left side of the variable oil chamber forming groove  76 . The guide land  71  is fitted in a guide member  77  arranged in a left end of the spool hole  6   d  and a variable oil chamber  78   a  encircled by the spool hole  6   d , the guide member  77  and the left land  74  is formed on the periphery of the variable oil chamber forming groove  76 . 
     Further, an oil reservoir forming hole  70   e  axially extended in the valve spool  70  is formed, a right end of the oil reservoir forming hole  70   e  is open, a modulator valve  150  is arranged, a left end is closed, and an orifice  70   d  is formed. As a result, the oil reservoir forming hole  70   e  is closed by the modulator valve  150  and an oil reservoir  78   b  is formed. A communicating hole  70   c  for making the variable oil chamber forming groove  76  and the oil reservoir forming hole  70   e  communicate is formed in the valve spool  70 , and the variable oil chamber  78   a  and the oil reservoir  78   b  connect via the communicating hole  70   c.    
     As described above, the shock absorbing mechanism is configured by the variable oil chamber  78   a  and the oil reservoir  78   b  which respectively connect via the communicating hole  70   c  and its operation will be described below. When the valve spool  70  is axially moved to the left, the capacity in the variable oil chamber  78   a  is reduced because the guide member  77  is fixed in the spool hole  6   d  and hydraulic fluid in the oil chamber is compressed by the left land  74 . At this time, as the capacity in the oil reservoir  78   b  cannot be varied, the compressive force functions as resistance, the movement of the valve spool  70  is inhibited, and is moderated. In the meantime, when the valve spool  70  is axially moved to the right, the capacity in the variable oil chamber  78   a  increases, however, resistance to force in a direction in which the capacity increases acts by adjusting (reducing) a diameter of the communicating hole  70   c , the movement of the valve spool  70  is inhibited, and is moderated. 
     The left end of the oil reservoir forming hole  70   e  is closed, however, the orifice  70   d  is formed, as oil flows in the orifice  70   d , the magnitude of the resistance is adjusted by the orifice  70   d . The orifice  70   d  is open to a coupling part for fining the fitting part  62   c  of the pressure receptor  62  and a left end of the valve spool  70  and the coupling part is lubricated by oil exhausted through the orifice  70   d.    
     In the shock absorbing mechanism configured as described above, the modulator valve  150  is attached so as to fill hydraulic fluid in the variable oil chamber  78   a  and the oil reservoir  78   b . Referring to  FIGS. 12 to 14 , the modulator valve will be described below. A communicating hole  70   a  that communicates with the modulator valve  150  is formed in the right groove  72  of the valve spool  70  and hydraulic fluid in the right groove  72  flows into the modulator valve  150  via the communicating hole  70   a . The modulator valve  150  includes a so-called pressure reducing valves and the hydraulic fluid in the right groove  72  is supplied to the oil reservoir  78   b  so that oil pressure in the oil reservoir  78   b  is held at a predetermined low pressure set by the modulator valve  150 . Therefore, a predetermined low-pressure hydraulic fluid set by the modulator valve  150  is ordinarily filled in the variable oil chamber  78   a  and the oil reservoir  78   b.    
     As oil in the oil reservoir  78   b  is ordinarily exhausted through the orifice  70   d , oil of the exhausted quantity is supplemented via the modulator valve  150 . As the supplemented oil is oil in the right groove  72  and the right groove  72  communicates with the oil passage  56  on the low pressure side or the oil passage  57  on the high pressure side according to an engaged/disengaged condition of the clutch, hydraulic fluid in the oil passage  56  on the low pressure side and the oil passage  57  on the high pressure side, that is, hydraulic fluid in the hydraulic closed circuit is used for supplemented oil. Therefore, the hydraulic fluid in the hydraulic closed circuit is ordinarily exhausted by the quantity of supplemented oil, the exhausted hydraulic fluid is replaced with fresh hydraulic fluid (a hydraulic fluid replacement system will be described later), and the temperature of the hydraulic fluid in the closed circuit can be prevented from rising. 
     Further, an exhaust hole  70   b  that pierces the valve spool from the oil reservoir  78   b  (the oil reservoir forming hole  70   e ) to the outside face of the left land  74  is formed in the valve spool  70  and an exhaust hole  6   e  that connects from the spool hole  6   d  to the outside is formed in the transmission output shaft  6 . As shown in  FIG. 13 , when the valve spool  70  is located in the partial clutch engagement, both exhaust holes  70   b ,  6   e  communicate via a peripheral groove  70   f  of the valve spool  70 . As a result, in the condition of partial clutch engagement, hydraulic fluid in the oil reservoir  78   b  is exhausted outside via both exhaust holes  70   b ,  6   e.    
     As described above, in the condition of partial clutch engagement, the inside passage  56  and the outside passage  57  partially communicate, as hydraulic fluid flows from the oil passage on the high pressure side to the oil passage on the low pressure side in the hydraulic closed circuit through the partial communicating part, the temperature of the hydraulic fluid in the hydraulic closed circuit easily rises. When hydraulic fluid in the oil reservoir  78   b  is exhausted outside via both exhaust holes  70   b ,  6   e  in the condition of partial clutch engagement as described above, hydraulic fluid of an exhausted quantity is supplemented via the modulator valve  150 . As the supplemented oil is oil in the right groove  72  and the right groove  72  communicates with the oil passage  56  on the low pressure side or the oil passage  57  on the high pressure side according to the engaged/disengaged condition of the clutch, hydraulic fluid in the oil passage  56  on the low pressure side and the oil passage  57  on the high pressure side, that is, hydraulic fluid in the hydraulic closed circuit is used for supplemented oil. Therefore, the hydraulic fluid in the hydraulic closed circuit is ordinarily exhausted by the quantity of supplemented oil, the exhausted oil is replaced with fresh hydraulic fluid (the hydraulic fluid replacement system will be described later), and the temperature of the hydraulic fluid in the closed circuit can be effectively prevented from rising particularly in the condition of partial clutch engagement. 
     As the valve spool  70  forming the clutch CL described above is an axially extended long cylindrical member and high dimensional precision is required for outside dimensions of the guide land  71  fitted in the guide member  77 , the central land  73  and the left land  74 , the valve spool is divided into a first spool member  171  and a second spool member  172 . Referring to  FIGS. 19(   a ) to  19 ( c ), the configuration will be described below. 
     The first spool member  171  is the cylindrical member provided with a fitted part  177   d  fitted to the fitting part  62   c  of the pressure receptor  62  at its left end provided with the guide land  71  fitted in the guide member  77  next to the fitted part. The guide land  71  is fitted in the guide member  77 , functions as a part for guiding the axial movement of the valve spool  70 , the fitted part functions as a part for sealing the variable oil chamber  78   a , and its outside dimension is required to be finished to have a high precision. 
     In the first spool member  171 , the variable oil chamber forming groove  76  is formed on the right side of the guide land  71  and at its right end, a fitting concave portion  171   a  in which a concentric fitting hole  171   b  is formed that axially extends inward and is open to the right end side. A first coupling hole  171   c  extending in a direction perpendicular to the axis is formed in the fitting concave portion  171   a  and an annular holding groove  171   d  concave in a circumferential direction is formed on the periphery of the first coupling hole  171   c.    
     In the meantime, in the second spool member  172 , a valve part which is provided with the right groove  72 , the central land  73 , the left groove  75  and the left land  74 , which executes communication/cutoff control between clutch oil passage or the inside branched oil passage  6   a  and the clutch oil passage or outside branched oil passages  6   b ,  6   c  and which executes clutch control are formed. In this valve part, the central land  73  and the left land  74  function as a valve as described above and their outside dimensions are required to be finished to have a high precision. 
     At a left end of the second spool member  172 , a fitting convex portion  172   a  having a concentric fitting protruded cylindrical face  172   b  protruded on the axial left side is provided. The fitting protruded cylindrical face  172   b  is formed in dimensions fitted into the fitting hole  171   b  and a second coupling hole  172   c  is pierced, the second coupling hole  172   c  is matched with the first coupling hole  171   c  in a condition fitted into the fitting hole  171   b  and extends in a direction perpendicular to the axis. 
     In the first spool member  171  and the second spool member  172  respectively configured as described above, a coupling pin  173  is inserted into the first and second coupling holes  171   c ,  172   c  matched in a condition in which the fitting convex portion  172   a  is fitted into the fitting concave portion  171   a , the first and second spool members are rockably coupled with the coupling pin  173  in the center to form the valve spool  70 . As a high dimensional precision is required for only the outside diameter of the guide land  71  in the first spool member  171  and for only the respective outside diameters of the central land  73  and the left land  74  in the second spool member  172  respectively by dividing the valve spool  70  into the first and second spool members  171 ,  172  as described above, the manufacture of these spool members is facilitated and the dimensional precision of the outside diameters can be easily enhanced. 
     As the coupling pin  173  is relatively moderately inserted into the first and second coupling holes  171   c ,  172   c , a ring  174  is fitted into the holding groove  171   d  to prevent the coupling pin  173  from falling out. As a result, the ring  174  is fitted with the ring covering an opening at a peripheral end of the first coupling hole  171   c  for closing both ends of the coupling pin  173 , and for preventing the coupling pin from falling out. 
     The ring  174  is formed in a coil by bending the wire, which is circular or rectangular in section, in a ring a plurality of times. Therefore, the ring  174  can be easily fitted into the holding groove  171   d  by spreading the diameter of the coil. End faces  174   a ,  174   b  on both sides of the ring  174  are worked to be flat and as shown in  FIG. 19(C) , the lateral width of the ring is equal overall. The lateral width is set to be slightly narrower than the width of the holding groove  171   d  and the ring  174  is fitted into the holding groove  171   d  without rattling. 
     In this embodiment, the ring  174  is formed by bending the wire in the ring a plurality of times to be the coil. However, the ring may be also formed by bending a thick wire into a ring only once. However, in this case, it is desirable that the ends are overlapped without clearance in a circumferential direction. An inside face of the ring  174  may also be attached to the holding groove  171   d  with a loose fit (with clearance). Thus, the valve spool  70  can be easily inserted into the spool hole  6   d.    
     In the hydrostatic continuously variable transmission CVT configured as described above, a lock-up mechanism  90  is provided, the lock-up mechanism  90  closes the hydraulic closed circuit to be a lock-up condition when a transmission gear ratio is 1.0, that is, when the input revolution speed of the hydraulic pump P and the output revolution speed of the hydraulic motor M are equal. Referring to  FIGS. 15 to 17 , the lock-up mechanism  90  will be described below. The lock-up mechanism  90  is provided with the motor eccentric member  91  slid on the end of the motor casing  30   b  as described above. The whole motor eccentric member  91  is formed in a ring and the motor-side cam ring  54  is arranged on its inside face  91   a . A fitting part  91   a  is formed at an upper end of the motor eccentric member  91 , is fastened to the motor casing  30   b  by a fitting pin  92 , and the motor eccentric member  91  is rockably attached to the motor casing  30   b  with the fitting pin  92  in the center. 
     To rock the motor eccentric member  91 , a lock-up actuator LA is attached to the motor casing  30   b  with the lock-up actuator located on the downside of the motor eccentric member  91 . The lock-up actuator LA is configured by a cylinder  96  is fixed to the motor casing  30   b , a piston  94  is slidably arranged in a cylinder hole of the cylinder  96 , a lid  95  that closes the cylinder hole and is attached to the cylinder  96  and a spring  97  that energizes the piston  94  toward the lid  95 . The cylinder hole is divided in two by the piston  94 , a lock-up hydraulic fluid chamber  96   a  and a lock-up release chamber  96   b  are formed, and a spring  97  is arranged in the lock-up release chamber  96   b . An end of the piston  94  is protruded outward from the cylinder  96  and the protruded part  94   a  is fastened to a coupling part  91   b  formed in a lower part of the motor eccentric member  91  via a coupling pin  93 . 
     In the lock-up mechanism  90  configured as described above, when the oil pressure of the lock-up hydraulic fluid chamber  96   a  is released, the piston  94  is moved on the side of the lid  95  by the energizing force of the spring  97  arranged in the lock-up release chamber  96   b . At this time, as shown in  FIG. 16 , the coupling part  91   b  is touched to an outer end face  96   c  of the cylinder  96 , in this condition, the center C 2  of the inside face  91   a  of the motor eccentric member  91  is eccentric with the center C 1  of the transmission output shaft  6  and the output rotor (the motor cylinder  32 ), and the motor eccentric member  91  is located in a normal position. 
     When the lock-up hydraulic fluid pressure is supplied to the lock-up hydraulic fluid chamber  96   a , the piston  94  is moved to the right against the energizing force by the spring  97  by the fluid pressure as shown in  FIG. 17  and the protruded part  94   a  is further protruded. Thus, the motor eccentric member  91  is rocked counterclockwise with the fitting pin  95  in the center as shown in  FIG. 17  and as shown in  FIG. 17 , a contact face  91   c  formed on the side of the motor eccentric member  91  is touched to a contact face  98   a  of a positioning projection  98  integrated with the motor casing  30   a . In this condition, the center C 2  of the inside face  91   a  of the motor eccentric member  91  is overlapped with the center C 1  of the transmission output shaft  6  and the output rotor (the motor cylinder  32 ) and the motor eccentric member  91  is located in a lock-up position. 
     As is known from the configuration of the hydraulic motor M and the configuration of the distributing valve  50  respectively described above, when the motor eccentric member  91  is located in the lock-up position, the center of the motor-side cam ring  54  arranged on the inside face  91   a  coincides with the rotational center of the motor cylinder  32 , even if the motor cylinder  32  is rotated, the motor-side spool  55  is not reciprocated, and the supply of high-pressure oil to the motor plunger  33  is cut off. At this time, the motor plunger communicates with the oil passage  56  on the low pressure side. As a result, a reduction in the compression loss and hydraulic fluid leakage in the motor plunger  33  and a reduction in the mechanical power loss of the bearing and others occurs because no high pressure is applied to the motor plunger  33 . Further, the reduction in resistance in sliding the pump-side spool  53  is enabled, and power transmission is efficiency enhanced. 
     As known from the above-mentioned description, when lock-up hydraulic fluid pressure is supplied to the lock-up hydraulic fluid chamber  96   a  in the lock-up mechanism  90 , the motor eccentric member  91  is rocked and is located in the lock-up position to be in the lock-up condition. That is, independent of the gear ratio of the hydrostatic continuously variable transmission CVT, if only lock-up hydraulic fluid pressure is supplied to the lock-up hydraulic fluid chamber  96   a , the lock-up condition can be hydraulically produced. However, as described above, as lockup should be made when the transmission gear ratio is 1.0, lockup is set so that lock-up hydraulic fluid pressure cannot be supplied unless the transmission gear ratio is in the vicinity of 1.0. Referring to  FIGS. 1 ,  4  and  20 , this configuration will be described below. 
     Lockup control oil passages  131 ,  132 ,  133  for supplying lock-up hydraulic fluid pressure to the lock-up hydraulic fluid chamber  96   a  are formed in the transmission housing HSG and the motor casing  30  ( 30   a ,  30   b ) as shown in the drawings. The lockup control oil passage  131  connecting with a lockup control oil pressure supply control valve not shown, is controlled by the valve, and lockup control oil pressure is supplied to the lockup control oil passage. The lockup control oil passage  133  connects with the lock-up hydraulic fluid chamber  96   a  of the lock-up mechanism  90 . Therefore, basically, an oil pressure supply control by the lockup control oil pressure supply control valve is executed and a lock-up operation control can be executed. 
     However, a branched oil passage  134  branched from the lockup control oil passage  132  is formed with the branched oil passage open to a concave supporting cylindrical face  30   c  formed on the inside face of the motor casing  30  and lock-up hydraulic fluid is exhausted in the casing from the branched oil passage  134  through an opening  134   a . A convex rocking supported cylindrical face  35   b  that forms the back side of the motor rocking member  35  that rotatably supports the motor swash plate  31  is slid on the supporting cylindrical face  30   c . In a condition wherein an angle of the swash plate is relatively large as shown in  FIGS. 1 and 4 , the opening  134   a  is open. In the meantime, as shown in  FIG. 20 , when the angle of the swash plate is in the vicinity of zero (a swash plate surface is in a direction perpendicular to the axis), the rocking supported face  35   b  covers and closes the opening  134   a  of the branched oil passage  134 . 
     As described above, when the angle of the swash plate is in the vicinity of zero which is substantially zero, that is, when transmission gear ration is in the vicinity of 1.0 which is substantially 1.0, the opening  134   a  of the branched oil passage  134  is closed. Therefore, only in the vicinity of a position of the swash plate angle in which the transmission gear ratio is 1.0 and lockup is required, the lockup control oil pressure can be supplied to the lock-up hydraulic fluid chamber  96   a  via the lockup control oil passages  131  to  133 . As the opening  134   a  of the branched oil passage  134  is open when an angle of the swash plate is except it, that is, when no lockup is required, lockup control oil pressure is exhausted in the casing through the branched oil passage  134  even if the lockup control oil pressure is supplied to the lockup control oil passage  131  and no lockup control oil pressure acts on the lock-up hydraulic fluid chamber  96   a.    
     Next, referring to  FIGS. 12 to 14  and  FIG. 18 , the configuration of a system for supplementing hydraulic fluid in the hydraulic closed circuit will be described. As shown in  FIG. 18 , hydraulic fluid is supplemented by the oil pump OP (see  FIG. 3 ) and discharged oil from the oil pump OP driven by the engine E is supplied to an oil passage  160  axially extending in the transmission output shaft  6  via an oil passage in the transmission housing HSG. The oil passage  160  connects with an oil passage  161  extending in a radial direction in the transmission output shaft  6  and opens to the periphery at the end of the oil passage  160 . The oil passage  161  further connects with oil passages  162   a ,  162   b ,  162   c  axially extending in the output rotor (the motor cylinder  32 , the valve body  51  and the pump cylinder  22 ), an orifice  164  communicating with the outside is formed at the end of the oil passage  162   c , and the inside of the transmission is lubricated by hydraulic fluid that flows outside from the orifice  164 . 
     A first check valve  170   a  for supplying supplemented oil to the outside passage  57  and a first relief valve  175   a  for relieving hydraulic fluid when oil pressure in the outside passage  57  exceeds a predetermined high pressure are provided in the pump cylinder  22  as shown in  FIGS. 12 to 14 . Further, a second check valve  170   b  for supplying supplemental oil to the inside passage  56  and a second relief valve  175   b  for relieving the hydraulic fluid when the oil pressure in the outside passage  57  exceeds a predetermined high pressure respectively having the similar configuration to the configuration of the above-mentioned valves are also provided though the two valves are not shown in  FIGS. 12 to 14 . 
     An oil passage  163   a  that connects the oil passage  162   c  and the first check valve  170   a  is formed in the pump cylinder  22  as shown in  FIGS. 12 to 14  and hydraulic fluid supplied from the oil pump OP is supplied to the outside oil passage  57  via the first check valve  170   a  as supplemented oil if necessary (according to leakage from the hydraulic closed circuit). The plurality of oil passages  162   a ,  162   b ,  162   c  are formed, an oil passage  163   b  that connects an oil passage  162   c  and a second check valve  170   b  is formed in the pump cylinder  22 , and hydraulic fluid supplied from the oil pump OP is supplied to the inside oil passage  56  via the second check valve  170   b  as supplemental oil if necessary (according to leakage from the hydraulic closed circuit). 
     Hydraulic fluid relieved from the first relief valve  175   a  when oil pressure in the outside passage  57  exceeds a predetermined high pressure set by energizing means is exhausted in a return oil passage  165   a  formed in the pump cylinder  22 . The return oil passage  165   a  communicates with a ring oil passage  166  formed on the periphery of the transmission output shaft  6  in a ring, fitted to the pump cylinder  22  and is encircled by the pump cylinder. The oil passage  166  communicates with the oil passage  162   c  via the oil passage  163   a  and as known, hydraulic fluid relieved from the first relief valve  175   a  is exhausted in an oil passage for supplying supplemented oil supplied from the oil pump OP. Hydraulic fluid relieved from the second relief valve  175   b  is also exhausted in the oil passage  162   c , that is, in a supplemented oil supply oil passage from the return oil passage  165   b  via the ring oil passage  166  and the oil passage  163   b  though the passages are not shown. 
     As described above, as hydraulic fluid relieved from the first and second relief valves  175   a ,  175   b  is exhausted in the supplemented oil supply oil passage  162   c  trough the return oil passages  165   a ,  165   b  and relieved oil is never returned to the hydraulic closed circuit. Thus, the rise in oil temperature in the hydraulic closed circuit can be inhibited. As oil pressure in the supplemented oil supply oil passage  162   c  is stable, hydraulic fluid in the oil passage on the high pressure side can be efficiently relieved. 
     As the supplemental oil supply oil passage extends from the transmission output shaft  6  into the output rotor, the first and second relief valves  175   a ,  175   b  and the return oil passages  165   a ,  165   b  are arranged in the pump cylinder  22  (the output rotor) and the return oil passages  165   a ,  165   b  connect with the supplemented oil supply oil passage  162   c  in the pump cylinder  22 , high-pressure relief structure is compactly housed in the pump cylinder  22  and can be made compact. Thus, the return oil passages  165   a ,  165   b  can be reduced. The return oil passages  165   a ,  165   b  connect with the supplemented oil supply oil passages  162   c  (and  163   a ,  163   b ) via the ring oil passage  166  circumferentially extending in the part fitted to the pump cylinder  22  on the outside face of the transmission output shaft  6  and the oil passages coupling structure in the part is simple. 
     The embodiment described above is a continuously variable transmission adopted for use in a motorcycle. However, the invention is not limited to being adopted for use in a motorcycle and can be adopted in various power transmission mechanism such as a four-wheel vehicle, a vehicle including an automobile and a general purpose machine. 
     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.