Abstract:
A hydrostatic continuously variable transmission comprises: a hydraulic pump; a power input shaft engaged with the hydraulic pump to transmit power from a power source to the hydraulic pump; a hydraulic motor in hydraulic communication with the hydraulic pump; a casing that houses the hydraulic pump and the hydraulic motor; a port block mounted to the casing, the port block having a block main body and a cover member connected to a power input side of the block main body, said cover member having an outer surface; a cooling hydraulic path provided in the port block in a region where the block main body and the cover member meet, the cooling hydraulic path being connected to a first hydraulic path in the port block, the cooling hydraulic path having a plurality of bends; a cooling fan provided on the power input shaft to provide air flow directly to the outer surface of the cover member.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a hydrostatic continuously variable transmission which is used as an automotive transmission in various work vehicles, such as a tractor, a lawnmower, a combine harvester, a rice transplanter, and the like. 
     In hydrostatic continuously variable transmissions (HSTs), hydraulic fluid needs to be cooled since the hydraulic fluid is heated by friction. For example, as disclosed in JP No. 8-145168 A, charge fluid pumped from a charging pump is cooled through an oil cooler before being supplied into a charge fluid path. 
     Conventionally, the oil cooler is provided in a cooling air path in a radiator of an engine, and the oil cooler is connected to related devices via external pipes. A number of parts for connecting the pipes are required, and piping requires much labor. 
     SUMMARY OF THE INVENTION 
     In view of this, an object of the present invention is to provide a simple cooling structure of a hydrostatic continuously variable transmission. 
     A hydrostatic continuously variable transmission in accordance with the present invention comprises: a hydraulic pump; a power input shaft engaged with the hydraulic pump to transmit power from a power source to the hydraulic pump; a hydraulic motor in hydraulic communication with the hydraulic pump; a casing that houses the hydraulic pump and the hydraulic motor; a port block mounted to the casing, the port block having a block main body and a cover member connected to a power input side of the block main body, said cover member having an outer surface; a cooling hydraulic path provided in the port block in a region where the block main body and the cover member meet, the cooling hydraulic path being connected to a first hydraulic path in the port block, the cooling hydraulic path having a plurality of bends; a cooling fan provided on the power input shaft to provide air flow directly to the outer surface of the cover member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a whole tractor; 
         FIG. 2  is a side view of a mission case; 
         FIG. 3  is a rear view of the mission case; 
         FIG. 4  is a front view of the mission case; 
         FIG. 5  is a plan view of the mission case; 
         FIG. 6  is a cross-sectional side view of a hydrostatic continuously variable transmission; 
         FIG. 7  is a cross-sectional front view of a port block; 
         FIG. 8  is a hydraulic circuit diagram; 
         FIG. 9  is a front view of a fan shroud; 
         FIG. 10  is a side view of a mower suspending and supporting structure; 
         FIG. 11  is a plan view of a lift arm for suspending a mower; and 
         FIG. 12  is an exploded perspective view of a lift arm assembly structure. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a general-purpose tractor which is an exemplary work vehicle in which a hydrostatic continuously variable transmission is used as an automotive transmission. The tractor is configured as a lawnmower, in which a mower  4  is linked to a lower portion of a four-wheel drive vehicle  3  comprising a small-diameter front wheel  1  which is controlled by a power steering operation, and a large-diameter rear wheel  2  (main drive wheel), in a manner which allows the mower  4  to freely move upward and downward. 
     The vehicle  3  includes a pair of left and right main frames  5  made of thick board material which are extending from the front to the rear. An engine  6  (power source) is provided at a front portion of the main frame  5  with a rotation axis center thereof being directed back and forth, and is covered with a bonnet  7 . A front axle case  8  which supports the front wheel  1  is linked to a lower front portion of the main frame  5  in a manner which allows the front axle case  8  to roll. A transmission case  11  to a front side of which a hydrostatic continuously variable transmission  10  is linked, is linked to a rear portion of the main frame  5 . A power output from the engine  6  is transmitted via a transmission shaft  51  to the hydrostatic continuously variable transmission  10 , in which the power is in turn subjected to continuously variable transmission in a forward or backward direction, and thereafter, is subjected to gear transmission in the transmission case  11 , so that the power is transmitted to the left and right rear wheels  2 . A portion of the traveling power is extracted toward the front of the vehicle and is transmitted via transmission shafts  52  and  53  to the front axle case  8 , in which the left and right front wheels  1  are in turn driven to the same speed as that of the rear wheel  2 . In addition, a portion of the power transmitted to the transmission case  11  is transmitted to a front PTO shaft  54  and a rear PTO shaft  55  without via the hydrostatic continuously variable transmission  10 . Working power which is extracted by the front PTO shaft  54  is transmitted via a telescopic transmission shaft  56  to a power input case  57  of the mower  4 . 
     The engine  6  is provided with a radiator  12  at the rear thereof. A cooling fan  13  which is driven by the engine power is provided between the engine  6  and the radiator  12 . A fan shroud  14  is provided, surrounding the cooling fan  13 . The fan shroud  14  is produced by resin molding. A cleaner case portion  15  is integrated with the fan shroud  14  at a front portion of the fan shroud  14 . As illustrated in  FIG. 9 , a large-diameter opening  15   a  is formed in a side wall of the cleaner case portion  15 . A cap  59  having an air vent  58  with a dust collector is detachably attached via a buckle  60  to the opening  15   a.  A boss portion  61  is integrated with the opening  15   a  at an inner deep portion of opening  15   a.  A cylinder-shaped cleaner element  16  is engaged with and supported by the boss portion  61 . By removing the cap  59  to open the opening  15   a,  the cleaner element  16  can be easily inserted or extracted for replacement from a lateral direction of the vehicle. A hose connecting opening  15   b  is formed in a front portion of the cleaner case portion  15  and is in communication with the boss portion  61 . The hose connecting opening  15   b  is connected in communication with an intake manifold  6   a  of the engine  6  via an intake hose  17 , so that air cleaned through the cleaner element  16  is taken into the engine  6  as air for combustion. 
     A pair of left and right lift arms  21  are provided above a rear portion of the transmission case  11  so as to move upward and downward a working apparatus linked to a rear portion of the vehicle via a three-point linking mechanism or the like (not shown). A single-action lift cylinder  22  for driving the lift arm  21  to swing is provided closer to one lateral side of the transmission case  11 . A gear pump  23  which is a hydraulic fluid supply source for the lift cylinder  22  and the like is externally linked to the rear portion of the transmission case  11  and is provided closer to the other lateral side of the transmission case  11  opposite to the lateral side to which the cylinder is closer. The gear pump  23  is linked to the transmission system in the transmission case  11  so that the gear pump  23  is driven in association with the transmission system. Note that, as illustrated in a hydraulic circuit diagram of  FIG. 8 , the flow of hydraulic fluid from the gear pump  23  is divided via a flow priority valve V 0 . The control flow is supplied to a controller PS of a power steering cylinder  65  for steering the front wheel, and a switching valve V 1  for switching on/off a multi-plate PTO clutch  66  present in a transmission system to the front PTO shaft  54  and the rear PTO shaft  55 . An excess flow from the flow priority valve V 0  is supplied to a control valve V 2  of the hydraulic cylinder  22  for driving the lift arm  21 . 
     The mower  4  is supported via a front link  25  and a rear link  26  which are linked to the main frame  5  in a manner which allows the mower  4  to translate upward and downward. A pair of left and right lift arms  28   a  and  28   b  are attached to rear portions of the main frames  5  via a supporting shaft  27 . The arms  28   a  and  28   b  are vertically swung in an integrated manner. The free ends of the lift arm  28   a  and  28   b  are linked to the left and right rear links  26 , respectively, via a middle link  29 . When the lift arms  28   a  and  28   b  are vertically swung, the mower  4  is moved upward and downward. The lift arms  28   a  and  28   b  can be retrofitted to the main frames  5 , and the attached structure will be described as follows. 
     Specifically, as illustrated in  FIGS. 11 and 12 , of the pair of left and right lift arms  28   a  and  28   b,  the right lift arm  28   b  is welded and fixed to the supporting shaft  27 , and the left lift arm  28   a  is detachably bolted to a linking flange  27   a  provided to the supporting shaft  27 . Substantially triangular attachment holes  30  for passing the linking flange  27   a  are formed in the right and left main frames  5 . The supporting shaft  27  is supported via a two-part structure bearing member (bearing members  31   a  and  31   b ) which is engaged and attached to the attachment hole  30  from the outside, in a manner which allows the supporting shaft  27  to freely rotate. 
     The lift arm is attached as follows. Initially, while the left lift arm  28   a  is detached, the supporting shaft  27  is inserted into the attachment hole  30  on the right side of the vehicle from the linking flange  27   a  side, and further, the linking flange  27   a  is protruded leftward and outward from the attachment hole  30  on the left side of the vehicle. Next, the bearing members  31   a  and  31   b  are fitted to the supporting shaft  27  outside the frame and are engaged with the substantially triangular attachment hole  30  in a manner which does not allow the bearing members  31   a  and  31   b  to rotate. Next, the lift arm  28   a  is bolted with an inner surface of the linking flange  27   a  exposed on the left side of the vehicle. Thereby, the left and right lift arms  28   a  and  28   b  are provided on both the left and right outer sides of the main frames  5  in a manner which allows the left and right lift arms  28   a  and  28   b  to swing in an integrated manner. In this state, the supporting shaft  27  is prevented by the left and right lift arms  28   a  and  28   b  and the bearing members  31   a  and  31   b  from moving in the axial direction, and the bearing members  31   a  and  31   b  cannot be pulled out of the attachment hole  30 . 
     An operation arm  28   c  is integrated with and extended from a base portion of the lift arm  28   a  attached to the linking flange  27   a.  A working arm  32  is extended downward from a base portion of the lift arm  21  provided on a left side of the rear portion of the transmission case  11 . The working arm  32  and the operation arm  28   c  are linked to each other via an association rod  33  so that the working arm  32  and the operation arm  28   c  are moved in association with each other. Therefore, when the lift arm  21  is raised by hydraulic drive, the working arm  32  is rotated in the same direction, so that the lift arms  28   a  and  28   b  swing in a direction which lifts the mower. When the lift arm  21  is lowered, the mower  4  goes downward due to its own weight. Note that the working arm  32  and the association rod  33  are linked with each other via a pin in an oblong hole guide  33   a  so that the mower  4  can be allowed to be lifted even in the fixed state of the working arm  32  when an upward external force is applied to the mower  4  since, for example, the mower  4  runs on a bump on the ground. 
     The hydrostatic continuously variable transmission  10  has an axial-plunger variable-capacity hydraulic pump  10 P and an axial-plunger fixed-capacity hydraulic motor  10 M, which are connected via speed control fluid paths a and b, as illustrated in the hydraulic circuit diagram of  FIG. 8 . The hydrostatic continuously variable transmission  10  is configured so that, by changing a discharging direction and a discharged amount of hydraulic fluid by changing an angle of a swash-plate of the pump  10 P, the rotational power of the motor  10 M can be continuously changed in a forward direction (advancing direction) or a backward direction (retreating direction). A circuit protecting safety valve  35  for limiting a circuit pressure, and a charge fluid path c for supplying hydraulic fluid to the speed control fluid paths a and b to compensate for hydraulic fluid leakage, are connected to the speed control fluid paths a and b. The charge fluid path c is connected in communication with a hydraulic fluid path e for supplying hydraulic fluid to the PTO clutch  66  so that hydraulic fluid is supplied via a check valve  37  to the speed control hydraulic fluid path “a” or the speed control hydraulic fluid path “b” on which charge fluid set by a relief valve  36  has a lower pressure. Excess hydraulic fluid which flows out of the relief valve  36  is returned to the transmission case  11  via a hydraulic fluid path d. 
     As illustrated in  FIG. 6 , a casing for the hydrostatic continuously variable transmission  10  has a speed change casing  41  which accommodates the pump  10 P and the motor  10 M and whose front side is open, and a port block  42  linked to the front side. A power input shaft  43  of the pump  10 P is protruded forward from the port block  42  and is linked to a rear end of the transmission shaft  51  extended from the engine  6 , while a power output shaft  44  of the motor  10 M is inserted into the transmission case  11  and is linked to a auxiliary gear speed change mechanism (not shown) in a manner which allows the power output shaft  44  to move in association with the auxiliary gear speed change mechanism. Note that the power input shaft  43  is inserted into the transmission case  11  and is linked to a PTO transmission system and a transmission system of the gear pump  23  in a manner which allows the power input shaft  43  to move in association with the PTO transmission system and the transmission system of the gear pump  23 . 
     The port block  42  has a thick-plate block main body  42   a  including the speed control fluid paths a and b and the charge fluid path c, and a cover member  42   b  bolted to a front side of an input side of the block main body  42   a.  As illustrated in  FIG. 7 , a meandering groove  45  (cooling hydraulic path) which has more than  10  bends, i.e. winds and turns in a complicated manner is formed on the front side of the block main body  42   a.  The cover member  42   b  is linked to the front side of the block main body  42   a,  so that a meandering hydraulic fluid path is formed in a junction portion of the block main body  42   a  and the cover member  42   b.  A hydraulic fluid input hole  46  and a hydraulic fluid output hole  47  are formed at respective ends of this hydraulic path. The hydraulic fluid input hole  46  is in communication with the charge hydraulic fluid path “c” through an excess hydraulic fluid output port of the relief valve  36 , while the hydraulic fluid hole  47  is in communication with the transmission case  11 . In other words, the meandering hydraulic fluid path formed in the port block  42  forms the hydraulic fluid path d for discharging excess hydraulic fluid. 
     In addition, the power input shaft  43  is provided with a cooling fan  48 . The cooling fan  48  supplies cooling air to an outer surface of the port block  42  from the front. Cooling fins  49  are formed on a front side of the cover member  42   b  provided on a front side of the port block  42  so that the cover member  42   b  is efficiently cooled by the cooling fan  48 . By forcedly cooling the port block  42  using air in this manner, hydraulic fluid flowing inside the block is cooled, and the hydraulic fluid path d which is caused to detour and flow inside the port block  42  serves as a hydraulic fluid path for cooling. 
     OTHER EXAMPLES  
     (1) In the above-described example, the groove  45  formed on the front side of the block main body  42   a  is sealed with the flat junction side of the cover member  42   b  to form the cooling hydraulic fluid path d. Conversely, the groove  45  can be formed only on a flat rear side of the cover member  42   b  to form the cooling hydraulic fluid path d at the junction portion of the block main body  42   a  and the cover member  42   b.  Alternatively, grooves  45  facing each other can be formed on the respective junction sides of the block main body  42   a  and the cover member  42   b  to form a cooling hydraulic fluid path d which has a large cross-sectional area. 
     (2) In the above-described example, an excess portion of the charge fluid supplied to the charge fluid path c is caused to flow in the cooling hydraulic fluid path d. Alternatively, a cooling hydraulic fluid path d may be provided between the charging pump CP and the charge fluid path c so that cooled charge fluid can be supplied to the charge fluid path c. 
     (3) The present invention can be applied to a work vehicle in which the hydrostatic continuously variable transmission  10  (the power input shaft  43 ) is provided in the vehicle  3 , pointing in a lateral direction or in a vertical direction. 
     (4) The port block body may be integrally formed with the speed change casing (HST casing)  41 . 
     (5) The hydraulic fluid input hole may be in communication with the speed control fluid path in stead of the charge hydraulic fluid path.