Abstract:
A work vehicle comprises: a plurality of wheels; a vehicle body supported by the wheels; a transmission case provided on the vehicle body, the transmission case having a first case portion and a second case portion and a middle portion extending between respective lower portions of the first and second case portions, the transmission case being divided by an abutting surface extending in a vertical direction of the vehicle; a hydraulic device associated with the transmission case; a hydraulic pump supplying a hydraulic fluid to the hydraulic device; an oil path formed in a surface of the abutting surface, one end of the oil path being formed in the first case portion as an oil port for the hydraulic device, and the other end of the oil path opening to the second case portion; and a hydraulic fluid outlet provided to the first case and connected to the hydraulic pump to supply hydraulic fluid to the hydraulic pump.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to the structure of a transmission case supporting the right and left rear wheels in a riding type mower.  
         [0002]     As disclosed for example in JP 2001-86831A, there are riding type mowers including a vehicle body supported by the right and left front wheels and the right and left rear wheels, a mower, and a grass collector at the rear of the vehicle body. A duct extending from the mower passes between the right and left rear wheels and is connected to the grass collector, so that the grass that has been cut by the mower is guided through the duct to the grass collector.  
         [0003]     In the mower disclosed in JP 2001-86831A, the transmission case comprises right and left supporting portions supporting the right and left rear wheels, and a middle portion that is located below the duct and that is connected to the right and left supporting portions. Thus, the motive power of the engine is transmitted from either the left or the right supporting portion of the transmission case to the light or left rear wheel, and transmitted to the left and right rear wheel from the right or left supporting portion on the other side of the transmission case, via a transmission shaft that is arranged in the middle portion of the transmission case.  
         [0004]     In JP 2001-86831A, the thin middle portion is connected between the right and left supporting portions of the transmission case. Thus, when hydraulic fluid is filled as lubricating oil into the transmission case (oil bath), the hydraulic fluid in the right and left supporting portions of the transmission case becomes difficult to circulate, so that the hydraulic fluid in the right and left supporting portions of the transmission case tends to stagnate.  
       SUMMARY OF THE INVENTION  
       [0005]     It is an object of the present invention to provide a riding type mower, whose transmission case includes first and second case portions and a middle portion connecting the first and second case portions, where there is little stagnation of the hydraulic fluid in different portions of the transmission case.  
         [0006]     To achieve this object, a work vehicle in accordance with an embodiment of the present invention comprises a plurality of wheels; a vehicle body supported by the wheels; a transmission case provided on the vehicle body, the transmission case having a first case portion and a second case portion and a middle portion extending between respective lower portions of the first and second case portions, the transmission case being divided by an abutting surface extending in a vertical direction of the vehicle; a hydraulic device associated with the transmission case; a hydraulic pump supplying a hydraulic fluid to the hydraulic device; an oil path formed in a surface of the abutting surface, one end of the oil path being formed in the first case portion as an oil port for the hydraulic device, and the other end of the oil path opening to the second case portion; and a hydraulic fluid outlet provided to the first case and connected to the hydraulic pump to supply hydraulic fluid to the hydraulic pump.  
         [0007]     With this configuration, hydraulic fluid returning from the hydraulic device circulates from the first case portion of the transmission case through the middle portion to the second case portion, and thus there is little stagnation of the hydraulic fluid in the first and second case portions of the transmission case.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is an overall lateral sectional view of a riding type mower.  
         [0009]      FIG. 2  is a vertical sectional view of a riding type mower taken from the rear.  
         [0010]      FIG. 3  is a diagrammatic lateral view of the transmission system from the engine to the transmission case, the hydrostatic continuously variable transmission, the right and left front wheels, the right and left rear wheels, and the mower.  
         [0011]      FIG. 4  is a vertical sectional lateral view of the vicinity of the left supporting portion of the transmission case.  
         [0012]      FIG. 5  is a vertical sectional view of the transmission case, taken from the rear.  
         [0013]      FIG. 6  is a sectional view of the vicinity of an abutting surface of the transmission case.  
         [0014]      FIG. 7  is a vertical sectional lateral view of the vicinity of a bearing in the left supporting portion of the transmission case.  
         [0015]      FIG. 8  is a vertical sectional view of the vicinity of the left supporting portion and the middle portion of the transmission case, taken from the rear.  
         [0016]      FIG. 9  is a vertical sectional lateral view of the vicinity of the right supporting portion of the transmission case.  
         [0017]      FIG. 10  is a diagram showing the hydraulic circuit configuration. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]     As shown in  FIG. 1 , in a riding type mower in accordance with an embodiment of the present invention, an engine  4  and a radiator  5  are supported at the front of a vehicle frame  3 , which is supported by right and left front wheels  1  and right and left rear wheels  2 . A operator&#39;s station  23  is supported above the middle of the vehicle frame  3 , and a mower  6  is supported below the middle of the vehicle frame  3 . A grass collector  7  is supported at the rear of the vehicle frame  3 .  
         [0019]     As shown in  FIG. 1 , the mower  6  is supported by a link  8  that is connected such that it is pivotable in vertical direction to the vehicle frame  3 . A link  10  is connected between the mower  6  and a lift cylinder  9  (see  FIG. 10 ; corresponds to the hydraulic device) in the vehicle frame  3 . The mower  6  is raised and lowered by the lift cylinder  9 . As shown in  FIGS. 1 and 2 , a duct  11  extending from the mower  6  passes between the left and rear wheels and is connected to the grass collector  7 , so that the grass that is cut by the mower  6  is guided through the duct  11  to the grass collector  7 .  
         [0020]     As shown in  FIG. 1 , a front axle case  12  is supported at the front of the vehicle frame  3 , and the right and left front wheels  1  are supported in a steerable manner by the front axle case. The right and left front wheels  1  are steered by a steering handle  13  that is provided in the operator&#39;s station  23 . A transmission case  14  and a hydrostatic continuously variable transmission  15  are fixed to the rear of the vehicle frame  3 , and the right and left rear wheels  2  are supported by the transmission case  14 . The motive force of the engine  4  is transmitted via a transmission shaft  16  to the hydrostatic continuously variable transmission  15  and to the right and left rear wheels  2 , and motive force is transmitted from the hydrostatic continuously variable transmission  15  via transmission shafts  17  and  18  and the front axle case  12  to the right and left front wheels  1 . Motive power that is branched off immediately before the hydrostatic continuously variable transmission  15  is transmitted via a transmission shaft  19  to the mower  6 .  
         [0021]     The following is a description of the structure of the transmission case  14 .  
         [0022]     As shown in  FIGS. 2 and 5 , the transmission case  14  includes a right supporting portion  20  supporting the right rear wheel  2  with a right axle  36 , a left supporting portion  21  supporting the left rear wheel  2  with a left axle  36 , and a middle portion  22  connected between the lower portions of the right and left supporting portions  20  and  21 . The duct  11  is positioned above the middle portion  22  of the transmission case  14 , between the right and left supporting portions  20  and  21  of the transmission case  14 . That is to say, the middle portion  22  of the transmission case  14  is positioned below the duct  11 .  
         [0023]     As shown in  FIGS. 6, 7 ,  8  and  9 , the right and left supporting portions  20  and  21  as well as the middle portion  22  of the transmission case  14  are each split into a front part and a rear part by abutting surfaces  20   a ,  21   a  and  22   a  extending in the lateral and vertical directions of the vehicle. As shown in  FIG. 5 , the front part of the right and left supporting portions  20  and  21  and the front part of the middle portion  22  of the transmission case  14  are formed in one piece. Also the rear part of the right and left supporting portions  20  and  21  and the rear part of the middle portion  22  of the transmission case  14  are formed in one piece. The front part of the right and left supporting portions  20  and  21  of the transmission case  14 , the front part of the middle portion  22 , the rear part of the right and left supporting portions  20  and  21  of the transmission case  14 , and the rear part of the middle portion  22  are linked by bolts  62  (see  FIGS. 6, 8  and  9 ).  FIG. 6  is a sectional view taken in the horizontal plane, and the upward direction in  FIG. 6  corresponds to the front direction of the vehicle. As shown in  FIGS. 1 and 2 , the hydrostatic continuously variable transmission  15  is linked to the rear surface of the rear part of the left supporting portion  21  of the transmission case  14 .  
         [0024]     As shown in  FIGS. 3, 4  and  5 , a frontward-pointing input shaft  24  is provided at the upper portion of the left supporting portion  21  of the transmission case  14 . A transmission shaft  14  is connected to the input shaft  24  so that the motive power of the engine  4  is transmitted via the transmission shaft  14  to the input shaft  24 . Inside the left supporting portion  21  of the transmission case  14 , the motive power of the input shaft  24  is transmitted to a hydraulic pump  15 P of the hydrostatic continuously variable transmission  15 , and transmitted to a hydraulic motor  15 M of the hydrostatic continuously variable transmission  15 . Motive power is transmitted from the hydrostatic continuously variable transmission  15  via an output gear  25 , transmission gears  26  and  27  and bevel gears  28  and  29  to a transmission shaft  30 . A fan  50  that is rotationally driven by the motive force of the input shaft  24  is provided, and cooling air from the fan  50  is directed at the hydrostatic continuously variable transmission  15 .  
         [0025]     As shown in  FIGS. 3, 4  and  5 , a transmission shaft  32  is rotatably supported by cylindrical bearing portions  22   b  and a bearing  31  in the right supporting portion  20  and the middle portion  22  of the transmission case  14 , and this transmission shaft  32  is arranged extending between the insides of the right supporting portion  20  and the middle portion  22  of the transmission case  14 . Below the left supporting portion  21  of the transmission case  14 , a transmission shaft  33  is rotatably supported by a cylindrical bearing portion  21   b  and a bearing  34 , and a differential  35  is provided between the transmission shafts  32  and  33 . A frontward-pointing output shaft  40  is provided at the upper portion of the left supporting portion  21  of the transmission case  14 , and the transmission shaft  17  is connected to this output shaft  40 .  
         [0026]     Thus, as shown in  FIGS. 3, 4  and  5 , motive force is transmitted from the hydrostatic continuously variable transmission  15  via the output shaft  25 , the transmission gears  26  and  27 , and the bevel gears  28  and  29  to the transmission shaft  30 , and the motive force of the transmission shaft  30  is transmitted via the transmission gear  37 , the differential  35 , the transmission shafts  32  and  33 , the transmission gears  38 , and the right and left axles  36  to the right and left rear wheels  2 . Motive force is also transmitted from the hydrostatic continuously variable transmission  15  via the output shaft  25 , the transmission gears  39  and  41 , the output shaft  40 , the transmission shafts  17  and  18 , and the front axle case  12  to the right and left front wheels  1 .  
         [0027]     As shown in  FIGS. 3, 4  and  5 , a frontward-pointing PTO shaft  42  is provided at the upper portion of the left supporting portion  21  of the transmission case  14 . The transmission shaft  19  is connected to the PTO shaft  42 , and a frictional multi-disk PTO clutch  43  is provided on the PTO shaft  42 . Thus, motive power is transmitted from the input shaft  24  to the mower  6  via a transmission gear  44 , a transmission gear  45 , a transmission gear  46 , the PTO clutch  43 , the PTO shaft  42  and the transmission shaft  19 . The transmission gear  45  is fitted onto the output shaft  40 , such that the two can rotate relatively to one another.  
         [0028]     The hydrostatic continuously variable transmission  15  can be set to a high-speed forward, a high-speed reverse and a neutral position, and is configured to provide continuously variable shifting. The hydrostatic continuously variable transmission  15  is operated with a change pedal (not shown in the drawings) provided in the operator&#39;s station  23 . As shown in  FIG. 4 , a trunnion shaft  47  is provided for operating the hydrostatic continuously variable transmission  15  to the high-speed forward, the high-speed reverse and the neutral position by changing the angle of an oblique plate (not shown in the drawings) in the hydraulic pump  15 P of the hydrostatic continuously variable transmission  15 . The trunnion shaft  47  protrudes out of the hydrostatic continuously variable transmission  15 , and the change pedal and the trunnion shaft  47  are mechanically linked.  
         [0029]     As shown in  FIG. 4 , a cam member  47   a  is fastened to the trunnion shaft  47  inside the hydrostatic continuously variable transmission  15 . An operating shaft  48  is provided in the hydrostatic continuously variable transmission  15 . An operating arm  48   a  is fastened to the operating shaft  48  inside the hydrostatic continuously variable transmission  15 , and a bearing  48   b  is supported by the operating arm  48   a . Outside the hydrostatic continuously variable transmission  15 , an operating arm  48   c  is fastened to the operating shaft  48 , and a spring  49  is connected to the operating arm  48   c  of the operating shaft  48 . Thus, the spring force of the spring  49  presses the operating arm  48   a  and the bearing  48   b  of the operating shaft  48  against the cam member  47   a  of the trunnion shaft  47 , and the trunnion shaft  47  (and hence the hydrostatic continuously variable transmission  15 ) is biased to the neutral position.  
         [0030]     The following is a description of the hydraulic circuit configuration.  
         [0031]     As shown in  FIG. 5 , hydraulic fluid is filled as lubricating oil into the transmission case  14 , and functions as an oil bath. The oil surface A of the hydraulic fluid is slightly above the PTO clutch  43 , near the output shaft  40 . As shown in  FIG. 10 , the hydraulic fluid in the transmission case  14  is supplied from a strainer  51  to a pump  52 , and then the hydraulic fluid is supplied from the pump  52  to a control valve  53 , a power steering mechanism  54  of the right and left front wheels  1  that are steered by the steering handle  13 , an oil cooler  55  (see  FIG. 1 ), a filter  56 , and the hydraulic circuit system of the hydrostatic continuously variable transmission  15 . From the hydraulic circuit system of the hydrostatic continuously variable transmission  15 , the hydraulic fluid is returned to the transmission case  14 .  
         [0032]     As shown in  FIGS. 3 and 4 , the pump  52  is coupled to the upper portion of the front part of the left supporting portion  21  of the transmission case  14 , and the motive force of the input shaft  24  is transmitted via transmission gears  57  and  58  to the pump  52 . The strainer  51  is provided at the lower portion of the rear part of the left supporting portion  21  of the transmission case  14 , and a duct  59  connects the strainer  51  with the pump  52 .  
         [0033]     As shown in  FIGS. 4, 5  and  10 , the control valve  53  (corresponding to a hydraulic device) is coupled to the upper portion of the front part of the left supporting portion  21  of the transmission case  14 . The control valve  53  can be switched between a lifted position in which the hydraulic fluid is supplied from the pump  52  to the lift cylinder  9 , so that the mower  6  is lifted up by the lift cylinder  9 , a stop position in which the hydraulic fluid is supplied from the pump  52  to the power steering mechanism  54 , and discharge of hydraulic fluid from the lift cylinder  9  is stopped, and a lowered position in which the hydraulic fluid is supplied from the pump  52  to the power steering mechanism  54 , and the hydraulic fluid is discharged from the lift cylinder  9 , so that the mower  6  is lowered up by the lift cylinder  9 . As shown in  FIG. 1 , a lift lever  61  is provided on the right-hand side of the driver seat  60  in the operator&#39;s station  23 , and the control valve  53  can be set with the lift lever  61  to the lifted position, the neutral position and the lowered position.  
         [0034]     The following is an explanation of the configuration for returning the hydraulic fluid from the control valve  53  to the transmission case  14 .  
         [0035]     As shown in  FIGS. 5, 6 ,  7 ,  8  and  9 , a series of grooves are formed along the abutting surface  21   a  on the right side (side of the duct  11 ) of the left supporting portion  21  of the transmission case  14 , the abutting surface  22   a  on the upper side of the middle portion  22  of the transmission case  14 , and the abutting surface  20   a  on the left side (side of the duct  11 ) of the right supporting portion  20  of the transmission case  14 . Oil paths  63  are formed with these grooves by coupling the front parts of the right and left supporting portions  20  and  21  and the front part of the middle portion  22  of the transmission case  14  to the rear part of the right and left supporting portions  20  and  21  and the rear part of the middle portion  22  of the transmission case  14 . A sealing member  64  is disposed outward from the oil path  63  in the abutting surface  21   a  of the left supporting portion  21  of the transmission case  14 , the abutting surface  22   a  of the middle portion  22  of the transmission case  14 , and the abutting surface  20   a  of the right supporting portion  20  of the transmission case  14 .  
         [0036]     As shown in  FIGS. 5, 7  and  8 , at the bearing  65  supporting the transmission shaft  30 , a groove portion is formed in the portion that is located on the outer circumference of the bearing  65  in the abutting surface  21   a  on the right side (side of the duct  11 ) of the left supporting portion  21  of the transmission case  14 , thus forming an oil path  63  with the groove and the circumferential portion of the bearing  65 . As shown in  FIGS. 5 and 8 , at the bearing portions  22   b  of the middle portion  22  of the transmission case  14 , oil path branches  66  that branch from the oil path  63  toward the bearing portions  22   b  of the middle portion  22  of the transmission case  14  are formed in the abutting surface  22   a  on the upper side of the middle portion  22  of the transmission case  14 .  
         [0037]     As shown in  FIGS. 5 and 9 , a ring-shaped groove portion  67  is formed at a portion supporting the right axle  36  at the abutting surface  20   a  on the left side (side of the duct  11 ) of the right supporting portion  20  of the transmission case  14 , a ring-shaped groove portion  68  that is in communication with the inside of the right supporting portion  20  of the transmission case  14  is formed from the groove portion  67 , and the oil path  63  is connected to the groove portion  67 . As shown in  FIG. 5 , the hydraulic fluid returning from the control valve  53  that is coupled to the upper portion of the front part of the left supporting portion  21  of the transmission case  14  is returned to the upper end of the oil path  63  in the left supporting portion  21  of the transmission case  14 .  
         [0038]     With the above-described configuration, as shown in  FIGS. 5, 6 ,  7 ,  8  and  9 , the hydraulic fluid returning from the control valve  53  is returned via the oil path  63  in the left supporting portion  21  of the transmission case  14 , the oil path  63  in the middle portion  22  of the transmission case  14 , the oil path  63  in the right supporting portion  20  of the transmission case  14 , and the grooves  67  and  68  to the inside of the right supporting portion  20  of the transmission case  14 . A portion of the hydraulic fluid of the oil path  63  in the middle portion  22  of the transmission case  14  is supplied via the oil path branches  66  to the bearing portions  22   b  of the middle portion  22  of the transmission case  14 . The hydraulic fluid that has been returned to the inside of the right supporting portion  20  of the transmission case  14  is returned to the inside of the left supporting portion  21  of the transmission case  14  through the inside of the middle portion  22  of the transmission case  14 .  
         [0039]     As shown in  FIGS. 5 and 8 , a plurality of block-shaped wall portions  22   c  through which the bolts  62  are passed are formed in the vehicle&#39;s longitudinal direction at the bottom of the middle portion  22  of the transmission case  14 . Thus, when the hydraulic fluid that has returned to the inside of the right supporting portion  20  of the transmission case  14  returns through the inside of the middle portion  22  of the transmission case  14  to the inside of the left supporting portion  21  of the transmission case  14  as described above, small debris in the hydraulic fluid is stopped by the wall portions  22   c  of the middle portion  22  of the transmission case  14 , so that any small debris in the hydraulic fluid accumulates near the wall portions  22   c  or between adjacent wall portions  22   c  of the middle portion  22  of the transmission case  14 .  
       Other Embodiments of the Invention  
       [0040]     In the configuration of the transmission case  14  described in the foregoing DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS, left and right as shown in  FIG. 5  may also be reversed (such that the hydrostatic continuously variable transmission  15  is coupled to the right supporting portion  20  of the transmission case  14 , moreover the input shaft  24 , the output shaft  40 , the PTO shaft  42  and the differential  35  are provided at the right supporting portion  20  of the transmission case  14 , and the pump  52  and the control valve  53  are coupled to the upper portion of the right supporting portion  20  of the transmission case  14 ).  
         [0041]     In the  FIGS. 5, 6 ,  7 ,  8  and  9  of the above-described DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS, it is also possible to form a series of grooves only in the abutting surface  21   a  on the right side (side of the duct  11 ) of the front part of the left supporting portion  21  of the transmission case  14 , the abutting surface  22   a  on the upper side of the front part of the middle portion  22  of the transmission case  14  and the abutting surface  20   a  on the left side (side of the duct  11 ) of the front part of the right supporting portion  20  of the transmission case  14 , to form the oil path  63 . Conversely, it is also possible to form a series of grooves only in the abutting surface  21   a  on the right side (side of the duct  11 ) of the rear part of the left supporting portion  21  of the transmission case  14 , the abutting surface  22   a  on the upper side of the rear part of the middle portion  22  of the transmission case  14  and the abutting surface  20   a  on the left side (side of the duct  11 ) of the front part of the right supporting portion  20  of the transmission case  14 , to form the oil path  63 .  
         [0042]     The present invention can be applied to any vehicle with a transmission case having a first and second case portions and a middle portion that connect lower portions of the first and second case portions. That is, a first and second case portions (although they correspond to the right and left supporting portions) do not have to be the right and left supporting portions that support right and left wheels respectively. In this case, the first and second case portions may be aligned, for example, in a fore-and-aft direction with respect to the vehicle and the corresponding abutting surface, that divides the transmission case and that defines the oil path, may extend in the corresponding direction, that is, vertical and fore-and-aft directions with respect to the vehicle.