Abstract:
A transaxle apparatus comprises: a housing; a hydrostatic transmission disposed in the housing, the hydrostatic transmission including a hydraulic pump receiving power from a prime mover, a first hydraulic motor driven in response to fluid supplied from the hydraulic pump, and a center section including an inner fluid passage for fluidly connecting the first hydraulic motor to the hydraulic pump; a first axle disposed in the housing and driven by the first hydraulic motor; a hydraulic actuator disposed outside the housing so as to drive a second axle disposed outside the housing; a port opened outside the housing so as to be fluidly connected to the hydraulic actuator; and a block interposed between the center section and the port in the housing, wherein a fluid passage is disposed in the block so as to connect the port to the inner fluid passage in the center section.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. application Ser. No. 11/170,149, filed Jun. 30, 2005, which is a continuation-in-part of U.S. application Ser. No. 11/033,543, filed Jan. 12, 2005, now U.S. Pat. No. 7,096,989, issued on Aug. 29, 2006, which is a division of U.S. Pat. application Ser. No. 10/270,378, filed Oct. 15, 2002, now U.S. Pat. No. 6,845,837, issued Jan. 25, 2005, the entire disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to a transaxle apparatus having a housing which incorporates a hydrostatic transmission (HST) and a hydraulic actuator arranged outside the housing which can be supplied with hydraulic fluid from the HST. More particularly, it relates to a four-wheel-drive articulated working vehicle.  
         [0004]     2. Related Art  
         [0005]     A well-known articulated riding lawn mower has first and second frames which are mutually pivotally coupled at proximal ends thereof so as to turn relatively to each other around a vertically axial pivot steering operation (i.e., manipulation of a steering wheel). The first frame is equipped with a prime mover and a transaxle apparatus which supports first axles driven by power from the prime mover. The second frame is equipped with a working device such as a mower device, an operating section, and an axle casing that supports second axles freely rotatably.  
         [0006]     In the Japanese Patent Laid Open Gazette 2000-270651, for example, is disclosed an articulated four-wheeled lawn mower, which includes as the first frame a rear frame and as the second frame a front frame. On the rear frame, a hydrostatic transmission (hereinafter, “HST”) is disposed, which transfers engine power to rear wheels supported by the rear frame. Moreover, in the rear frame is disposed a power take-off shaft, which receives power from a pump shaft of a hydraulic pump of the HST. The pump shaft revolves synchronously to the engine power output revolution. The revolution of the pump shaft is transferred to the mower device supported by the front frame.  
         [0007]     Generally, as to each of vehicles having the above structure, while the first axles supported by the transaxle apparatus of the first frame (usually serving as a rear frame) is driven by the prime mover, the second axles supported by the axle casing of the second frame (usually serving as a front frame) revolve freely and not in driving association with the power for driving the axles of the first frame. Thus, the vehicle is a so-called two-wheel drive vehicle.  
         [0008]     However, while the two-wheel-drive vehicle which drives only rear wheels exhibits superior steering performance, it lacks stability when working on a slope and roadability when running on a bad road. Further, if the vehicle is an articulated vehicle, the steering performance must be improved because the vehicle is bent at the coupling part of the frames. Moreover, the vehicle is difficult to bail out if it becomes stuck, such as in mud, etc.  
         [0009]     For solving these problems, a four-wheel-drive design, which drives both front and rear wheels, is desirable for the articulated vehicle. The rear frame of the vehicle disclosed in the above document is provided with an HST and a power take-off shaft for transferring power to the working device. However, as mentioned above, since the power take-off shaft revolves synchronously with the revolution of the pump shaft, the rotary speed of the pump shaft is fixed as long as the engine speed is fixed. On the other hand, the rotary speed of the rear wheels, which are driven by the power output of the hydraulic motor, is changed variably by a running speed changing operation which adjusts the angle of a movable swash plate of the hydraulic pump. Therefore, the power take-off shaft for driving the working device cannot be used as a front wheel drive shaft. Even if another power take-off shaft for front-wheel-drive, whose rotation is synchronized with the power output of the HST for rear wheel drive, can be connected to the transaxle apparatus mounted in the rear frame, severe limitations exist for such an arrangement to infix additional mechanical transmission system between front and rear transaxle apparatuses, because the turning of front and rear frames must be permitted, as well as infixing the transmission system for the working device drive therebetween.  
       SUMMARY OF THE INVENTION  
       [0010]     An object of the present invention is to provide a transaxle apparatus including a housing containing an HST so as to supply hydraulic fluid from the HST to a hydraulic actuator for driving wheels arranged outside of the housing, thereby constituting a driving system for a four-wheel driving vehicle, such as an articulated vehicle.  
         [0011]     To achieve the object, a transaxle apparatus according to the invention comprises: a housing; a hydrostatic transmission disposed in the housing, wherein the hydrostatic transmission including a hydraulic pump receiving power from a prime mover, a first hydraulic motor driven in response to fluid supplied from the hydraulic pump, and a center section including an inner fluid passage for fluidly connecting the first hydraulic motor to the hydraulic pump; a first axle disposed in the housing and driven by the first hydraulic motor; a port opened outside the housing and fluidly connected to a hydraulic actuator disposed outside the housing so as to drive a second axle disposed outside the housing; and a block interposed between the center section and the port in the housing. A fluid passage is disposed in the block so as to connect the port to the inner fluid passage in the center section.  
         [0012]     Preferably, a pair of the ports are fitted to the block.  
         [0013]     Preferably, the port has a flexible portion to which a pipe to the hydraulic actuator is connected.  
         [0014]     Preferably, the hydraulic actuator disposed outside the housing is a second hydraulic motor.  
         [0015]     These and other objects, features, and advantages of the invention will become more apparent upon a reading of the following detailed description and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a side view of a riding lawn mower as an embodiment of a four-wheel-drive articulated working vehicle according to the present invention.  
         [0017]      FIG. 2  is a plan view partly in section of the vehicle of  FIG. 1 .  
         [0018]      FIG. 3  is a rear view partly in section of a front transaxle apparatus  10  provided in the vehicle of  FIG. 1 .  
         [0019]      FIG. 4  is a plan view of the front transaxle apparatus  10  of the present invention from which an upper housing half  46  is removed.  
         [0020]      FIG. 5  is a fragmentary rear view partly in section of the front transaxle apparatus  10  of the present invention, showing a hydraulic motor  40  disposed therein.  
         [0021]      FIG. 6  is a sectional left side view of the front transaxle apparatus  10  of the present invention.  
         [0022]      FIG. 7  is a right side view of a rear transaxle apparatus  20 .  
         [0023]      FIG. 8  is a plan view partly in section of the rear transaxle apparatus  20  according to the first embodiment of the present invention from which an upper housing half  246  is removed, showing that a center section  260  having ports for series connection is disposed therein.  
         [0024]      FIG. 9  is a rear view partly in section of the rear transaxle apparatus  20  according to the first embodiment.  
         [0025]      FIG. 10  is a fragmentary sectional plan view of the rear transaxle apparatus  20  according to the first embodiment, showing the fluid passage structure formed in the center section  260  disposed therein.  
         [0026]      FIG. 11  is a fragmentary sectional side view of the rear transaxle apparatus  20  according to the first embodiment of the present invention.  
         [0027]      FIG. 12  is a hydraulic circuit diagram showing the hydraulic motor  240  of the rear transaxle apparatus  20  according to the first embodiment of the present invention and the hydraulic motor  40  of the front transaxle apparatus  10  are fluidly connected to the hydraulic pump  230  of the rear transaxle apparatus  20  in series.  
         [0028]      FIG. 13  is a hydraulic circuit diagram of the motor of  FIG. 12 , showing a case where the hydraulic motor  40  of the front transaxle apparatus  10  is exchanged for a variable displacement type.  
         [0029]      FIG. 14  is a rear view partly in section of the rear transaxle apparatus  20  according to another embodiment having ports for series connection, where a fluid passage member  307  is passed.  
         [0030]      FIG. 15  is a rear view partly in section of the same where a fluid passage member  302  is passed.  
         [0031]      FIG. 16  is a side view partly in section of the same.  
         [0032]      FIG. 17  is a plan view partly in section of the same.  
         [0033]      FIG. 18  is a rear view partly in section of the rear transaxle apparatus  20  according to another embodiment having ports for series connection of another construction.  
         [0034]      FIG. 19  is a side view partly in section of the rear transaxle apparatus  20  according to another embodiment having ports for series connection of further another construction.  
         [0035]      FIG. 20  is a bottom view partly in section of an interior of the rear transaxle apparatus  20  according to another embodiment, having other ports for the series connection with the front transaxle apparatus.  
         [0036]      FIG. 21  is a sectional side view of the rear transaxle apparatus  20  according to the embodiment of  FIG. 20 .  
         [0037]      FIG. 22  is a cross sectional view taken along XXII-XXII line of  FIG. 21 .  
         [0038]      FIG. 23  is a plan view partly in section of a rear transaxle apparatus  20  according to a second embodiment of the present invention from which an upper housing half  246  is removed, showing that a center section  360  having ports for parallel connection is disposed therein.  
         [0039]      FIG. 24  is a rear view partly in section of a portion of the rear transaxle apparatus  20  according to the second embodiment where a third passage is passed.  
         [0040]      FIG. 25  is a rear view partly in section of another portion of the transaxle of  FIG. 24  where a fourth passage is passed.  
         [0041]      FIG. 26  is a fragmentary sectional plan view of the rear transaxle apparatus  20  according to the second embodiment, showing fluid passage structure formed in the center section  360 .  
         [0042]      FIG. 27  is a fragmentary sectional side view of the rear transaxle apparatus  20  according to the second embodiment.  
         [0043]      FIG. 28  is a hydraulic circuit diagram showing the hydraulic motor  340  of the rear transaxle apparatus  20  according to the second embodiment and the hydraulic motor  40  of the front transaxle apparatus  10  are fluidly connected in parallel to the hydraulic pump  230  of the rear transaxle apparatus  20 .  
         [0044]      FIG. 29  is a plan view partly in section of a four-wheel-drive articulated working vehicle in which front transaxle apparatuses  400 L and  400 R having respective hydraulic motors are provided to right and left front wheels, respectively.  
         [0045]      FIG. 30  is a rear view partly in section of the right and left front transaxle apparatuses  400 L and  400 R provided to the working vehicle.  
         [0046]      FIG. 31  is a plan view partly in section of the front transaxle apparatuses  400 R ( 400 L) provided to the working vehicle.  
         [0047]      FIG. 32  is a hydraulic circuit diagram showing that a hydraulic motor  240  of the rear transaxle apparatus  20  according to the first embodiment of the present invention and a circuit which fluidly connects hydraulic motors  440  of both the front transaxle apparatuses  400 L and  400 R to each other in parallel are fluidly connected in series to the hydraulic pump  230  of the rear transaxle apparatus  20 .  
         [0048]      FIG. 33  is a hydraulic circuit diagram of the present invention in a case that variable displacement hydraulic motors serve as both the hydraulic motors  440 .  
         [0049]      FIG. 34  is a hydraulic circuit diagram showing the hydraulic motor  240  of the rear transaxle apparatus  20  according to the first embodiment and the hydraulic motors  440  of both the front transaxle apparatuses  400 L and  400 R are fluidly connected in series to the hydraulic pump  230  of the rear transaxle apparatus  20 .  
         [0050]      FIG. 35  is a hydraulic circuit diagram showing the hydraulic motor  240  of the rear transaxle apparatus  20  according to the second embodiment of the present invention and the hydraulic motors of both the front transaxle apparatuses  400 L and  400 R are fluidly connected in parallel to the hydraulic pump  230  of the rear transaxle apparatus  20 .  
         [0051]      FIG. 36  is a hydraulic circuit diagram showing the hydraulic motor  240  of the rear transaxle apparatus  20  according to the second embodiment of the present invention and a circuit, which fluidly connects in series the hydraulic motors of both the front transaxle apparatuses  400 L and  400 R to each other, are fluidly connected in parallel to the hydraulic pump  230  of the rear transaxle apparatus  20 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0052]     Description will be given of a four-wheel-drive articulated working vehicle according to the present invention.  
         [0053]      FIGS. 1 and 2  show a working vehicle equipped at a front portion thereof with a mower device  3  serving as a working device. A front frame  11  is provided with a front transaxle apparatus from which front wheel axles  12 L and  12 R are extended in a transverse direction and fixed to respective front wheels  13 . A rear frame  21  is provided with a rear transaxle apparatus from which rear wheel axles  22 L and  22 R are extended in a transverse direction and fixed to respective rear wheels  23 .  
         [0054]     A rear end portion of the front frame  11  is horizontally rotatably coupled to a front end portion of the rear frame  21  through a coupling part  50 . Coupling part  50  constitutes a pivot point of rotation of both the frames. Thus, the working vehicle including the horizontally turnable front and rear frames  11  and  21  is bendable at the intermediate portion thereof, thereby being a so-called articulated vehicle.  
         [0055]     A steering column  14 , a steering wheel  4 , and a pedal  15  are arranged in a front portion of front frame  11 , and a seat  9  is disposed behind steering column  14 , thereby constituting an operation part  16  on front frame  11 . Mower device  3  is vertically movably provided at a distal end of front frame  11 , that is, at a downwardly forward position from operation part  16 . Mower device  3  is driven by an engine  5 .  
         [0056]     As shown in  FIGS. 1 and 2 , on rear frame  21  is disposed engine  5  covered with a bonnet  8 . A rear transaxle apparatus is arranged under engine  5 .  
         [0057]     On the rear frame  21  end, a first engine output pulley  94  is fixed to an output shaft  93  of engine  5 , an HST input pulley  292  is fixed to a pump shaft  231  of a hydraulic pump incorporated in the rear transaxle apparatus, and a second engine output pulley  96  (shown in  FIG. 1 ) is fixed to output shaft  93  under first engine output pulley  94 .  
         [0058]     On the front frame  11  end, a working device drive power input pulley  111  is fixed to a power input shaft  112  of mower device  3  as a working device, and an idle pulley  98  is rotatably supported through a bearing (not shown) on a support shaft  97  suspended from front frame  11 .  
         [0059]     Moreover, as shown in  FIGS. 1 and 2 , regarding coupling part  50 , a cylindrical pivotal connector  28  is disposed on the laterally middle front end of rear frame  21  and not-relatively rotatably supports a joint shaft  55  in the vertical direction. A platy pivotal connector  18 , which is U-shaped in side view, is pivotally coupled to joint shaft  55 . Thus, rear frame  21  and front frame  11  are pivotally coupled so as to be horizontally turnable. In this way, pivotal connectors  18  and  28  are provided at the respective proximal ends of frames  11  and  21 , each of which faces to the proximal side of the vehicle, and are pivotally connected to each other through joint shaft  55  so as to constitute coupling part  50 . Thus, both frames  11  and  21  are arranged in tandem and coupled so as to be turnable around joint shaft  55 , thereby enabling the vehicle to be steered.  
         [0060]     A lower end of joint shaft  55  is extended below pivotal connector  18  so as to support a power output pulley  57  and a power input pulley  56  rotatably thereon through bearings (not shown).  
         [0061]     As shown in  FIGS. 1 and 2 , on rear frame  21  end, a rear drive transmission belt  92  is wound around the first engine output pulley  94  and HST input pulley  292 , and a first working-device drive transmission belt  58  is wound around the second engine output pulley  96  and power input pulley  56 .  
         [0062]     On front frame  11  end, second working-device drive transmission belt  59  is wound around an idle pulley  98  ( FIG. 2 ), a working-device drive power input pulley  111 , and power output pulley  57 .  
         [0063]     Due to this construction, engine output is transmitted to HST input pulley  292  through rear drive transmission belt  92  from first engine output pulley  94  so as to rotate pump shaft  231 . The engine output is also transmitted to working-device drive power input pulley  111  through second engine output pulley  96 , first working-device drive transmission belt  58 , power input pulley  56 , power output pulley  57  integrally rotating power input pulley  56 , and second working-device drive transmission belt  59 , so as to rotate a power input axis  112 , thereby rotating mowing blades  17 .  
         [0064]     As shown in  FIG. 2 , at a position shifted leftward from lateral middle of front frame  11  is disposed front transaxle apparatus, which supports left and right front wheel axles  12 R and  12 L so as to extend right front wheel axle  12 R longer than left wheel axle  12 L.  
         [0065]     As shown in  FIGS. 2 and 3 , a pair of left and right collars  99   a  and  99   b  are freely rotatably on right front wheel axle  12 R at a substantially laterally middle position of front frame  11 . The lower surfaces of second working-device drive transmission belt  59  comes into contact with the respective upper surfaces of collars  99   a  and  99   b.    
         [0066]     Hence, front transaxle apparatus supports the pair of axles whose lengths are different from each other, and second working-device drive transmission belt  59 , serving as a transmission element for drivingly connecting engine  5  and mower device  3  to each other, crosses the longer axle of the pair; in other words, second working-device drive transmission belt  59  changes direction by contacting collars  99   a  and  99   b  on the longer axle.  
         [0067]     In this way, second working-device drive transmission belt  59  passes above front wheel axle  12 R so as not reduce the road clearance. Moreover, since collars  99   a  and  99   b  are idled, second working-device drive transmission belt  59  is not damaged by friction.  
         [0068]     Next, description will be given of the front transaxle apparatus. As shown in  FIG. 6 , an upper housing half  46  and a lower housing half  47  are vertically joined to each other so as to form one housing, which provides the external appearance of the front transaxle apparatus  10  and contains within its interior a fluid sump and for incorporating the hydraulic motor, etc.  
         [0069]     As shown in  FIG. 4 , a counter shaft  139 , on which a reduction-gear train  135  is freely provided, divides the hollow interior of the housing into a first chamber  10   a , which incorporates a differential gear unit  120 , and a second chamber  10   b , which incorporates a hydraulic motor  40 . Driving force of hydraulic motor is transmitted to differential gear unit  120  through reduction-gear train  135 .  
         [0070]     As shown in  FIG. 5 , hydraulic motor is integrally disposed within front transaxle apparatus. On a vertical portion of center section  62  is formed a motor mounting surface  63   m  (shown in  FIG. 16 ) on which a cylinder block  43  is rotatably and slidably supported. A plurality of pistons  42  are reciprocally movably fitted through respective biasing springs into a plurality of cylinder bores in cylinder block  43 . A thrust bearing  44   a  of a fixed swash plate  44  abuts against the heads of pistons  42 . An opening  44   b  is provided in the center of fixed swash plate  44  so as to allow motor shaft  41  to pass therethrough. Fixed swash plate  44  is fixedly sandwiched between upper housing half  46  and lower housing half  47 .  
         [0071]     Motor shaft  41  is rotatably supported by a sealed bearing  45  held on the joint surface between upper housing half  46  and lower housing half  47 .  
         [0072]     Motor shaft  41  is not-relatively rotatably engaged with cylinder block  43  so as to be disposed horizontally on the rotary axis of cylinder block  43  and serve as an output shaft.  
         [0073]     In this way, front transaxle apparatus  10  contains an axial piston type hydraulic motor  40 .  
         [0074]     Moreover, as shown in  FIG. 6 , a pair of first and second kidney ports  62   a  and  62   b  are formed in motor mounting surface  63   m  formed on the vertical portion of center section  62 . First and second kidney ports  62   a  and  62   b  are connected to, respectively, horizontal first and second fluid passages  53   a  and  53   b  bored within center section  62 . As shown in  FIG. 4 , first fluid passage  53   a  and second fluid passage  53   b  are connected to respective caps  54   a  and  54   b  to which hydraulic hoses are connected. Thus, hydraulic motor  40  is fluidly connected to hydraulic pump  230  through hydraulic hoses (not shown).  
         [0075]     As shown in  FIG. 5 , a bypass operation lever  65  for opening first fluid passage  53   a  and second fluid passage  53   b  to the fluid sump is disposed above upper housing half  46  in order to enable the axles ( 12 L and  12 R) to idle when the vehicle is towed. Bypass operation lever  65  is fixed at a basal portion thereof to an upper end of a vertical bypass lever shaft  66  rotatably supported by an upper wall of upper housing half  46 . Bypass lever shaft  66  extends at a lower end thereof to the interior of center section  62  so as to be horizontally slidably in center section  62 . A flat surface  66 a is formed in a lower end side of bypass lever shaft  66  so as to contact an end face of a push pin  67  which is allowed to contact the rotationally sliding surface of cylinder block  43 .  
         [0076]     As shown in  FIG. 6 , a feeding-and-discarding port  46   a  is formed in the upper portion of upper housing half  46  so as to enable hydraulic fluid to be fed or discharged from and to a reservoir tank (not shown).  
         [0077]     As shown in  FIGS. 4 and 5 , a drive output gear  131  is fitted with spline onto an end of motor axis  41  opposite to center section  62  so as to be rotated integrally with motor shaft  41 . On the side of drive output gear  131  facing section  62  is integrally formed a brake rotor  133  whose diameter is larger than that of drive output gear  131 . Brake rotor  133  is sandwiched between brake pads  134   a  and  134   b  ( FIG. 4 ) so as to brake rotating motor shaft  41 .  
         [0078]     As shown in  FIG. 4 , a counter shaft  139  is arranged parallel to motor shaft  41 , a wide, small diameter gear  137  fits loosely on counter shaft  139 , and a large diameter gear  136  is engaged with a toothed side portion of small diameter gear  137 , thereby forming reduction-gear train  135 .  
         [0079]     Regarding reduction-gear train  135 , while large diameter gear  136  engages with drive output gear  131 , small diameter gear  137  engages with a ring gear  121  of differential gear unit  120 , thereby transmitting driving force of motor shaft  41  to differential gear unit  120  through reduction-gear train  135 .  
         [0080]     Moreover, differential gear unit  120  comprises ring gear  121 , which engages with small diameter gear  137  of reduction-gear train  135 , pinions  123 , which are rotatably supported by respective pinion shafts  122  which project inward from an inner periphery of ring gear  121 , and side gears  124  fixed to respective front wheel axles  12 L and  12 R and laterally engaged with each of pinions  123 . Due to this construction, the driving force from motor shaft  41  is transmitted to front wheel axles  12 L and  12 R through reduction-gear train  135 , ring gear  121 , pinions  123 , and side gears  124 .  
         [0081]     As shown in  FIGS. 4 and 5 , an end of motor axis  41 , which is opposite to cylinder block  43 , is extended outside of the housing so as to be fixedly provided thereon with a cooling fan  191  for cooling fluid collected in the front transaxle apparatus.  
         [0082]     Description will now be given of the rear transaxle apparatus. As shown in  FIG. 2 , hydraulic motor  40  incorporated in front transaxle apparatus  10 , which drives front wheel axles  12 L and  12 R, is fluidly connected through hydraulic hoses  81   a  and  81   b  to a hydraulic motor incorporated in the rear transaxle apparatus  20 , which drives rear wheel axles  22 L and  22 R.  
         [0083]     As shown in  FIGS. 8 and 9 , rear transaxle apparatus comprises a housing which is formed by an upper housing half and a lower housing half  247  vertically separably joined to each other so as to form a hollow interior into which the hydraulic motor, etc., is incorporated.  
         [0084]     The housing forms a bearing portion for a later-discussed motor shaft  241  on the joint surface thereof between housing halves  246  and  247 , and forms a bearing portion for journaling rear wheel axles  22 L and  22 R in the upper housing half above the joint surface. Rear wheel axles  22 L and  22 R are differentially connected at inner ends thereof to each other through a differential gear unit  220 , and extended outward from respective left and right outside walls of the housing.  
         [0085]     As shown in  FIG. 8 , rear transaxle  20  apparatus is integrally formed therein with an internal wall  248  which divides the inner space of rear transaxle  20  apparatus into first and second chambers  20   a  and  20   b.  In first chamber  20   a  is disposed an HST  290 , and in second chamber  20   b  are disposed a drive train  249  comprising a gear train which transmits power to differential gear unit  220  from motor shaft  241 , differential gear unit  220 , and inner side ends of rear wheel axles  22 L and  22 R.  
         [0086]     Internal wall  248  comprises a longitudinal portion parallel to rear wheel axles  22 L and  22 R, and a perpendicular portion extended perpendicularly to the longitudinal portion. These two portions are provided continuously so as to arrange first chamber  20   a  adjacent to second chamber  20   b.  An upper wall portion of internal wall  248  extends downward from an inner upper wall surface of upper half housing  246 , and a lower portion of internal wall  248  rises from the inner bottom surface of lower half housing  247  through the joint surface. By joining upper and lower housings  246  and  247 , end faces of both the upper and lower wall portions are also joined to each other so as to form internal wall  248 , thereby dividing the inner space into first and second chambers  20   a  and  20   b  which are independent of each other.  
         [0087]     In the housing, first chamber  20   a  is disposed in front of rear wheel axle  22 R and on a lateral side of drive train  249  which transmits power to differential gear unit  220  from motor shaft  241 .  
         [0088]     In first chamber  20   a  is detachably settled a center section  260  of the HST. A longitudinal portion of center section  260  is extended rectangularly to rear wheel axles  22 L and  22 R, and a vertical surface is formed on a front portion of the longitudinal portion so as to serve as a motor mounting surface  260   m,  onto which the hydraulic motor is mounted. A horizontal surface is formed on the rear portion of center section  260  so as to serve as a pump mounting surface  260   p,  onto which the hydraulic pump is mounted. In the center of pump mounting surface  260   p  is vertically supported a pump shaft  231 .  
         [0089]     Description will now be given of the hydraulic pump arranged on center section  260 .  
         [0090]     As shown in  FIG. 9 , a cylinder block  233  is rotatably and slidably disposed on pump mounting surface  260   p  which is formed at the horizontal portion of center section  260 .  
         [0091]     Pistons  232  are reciprocally movably fitted through respective biasing springs into a plurality of cylinder bores in cylinder block  233 . A thrust bearing  234   a  of a movable swash plate  234  abuts against the heads of pistons  232 . An opening  234   b  is provided at the center of movable swash plate  234  so as to allow a pump shaft  231  to pass therethrough. A control arm  238  engages with a side of movable swash plate  234  so that a tilt angle of movable swash plate  234  is adjusted by rotating a control shaft  237  serving as a rotary shaft of control arm  238 .  
         [0092]     In order that pump shaft  231  may function as an input shaft, pump shaft  231  is rotatably supported by a bearing  235  engaged in an opening  236  formed above first chamber  20   a  in upper half housing  246  and is not-relatively rotatably engaged with cylinder block  233 , thereby being arranged vertically on the rotary axis of cylinder block  233 .  
         [0093]     In this way, an axial piston type variable displacement hydraulic pump is constructed in rear transaxle apparatus.  
         [0094]     As shown in  FIG. 9 , the upper end of pump shaft  231  projects outwardly from the rear transaxle apparatus. An HST input pulley  292  and a cooling fan  291  are fixed onto the upper end of pump shaft  231 . Thus, while cooling the hydraulic fluid accumulated in rear transaxle apparatus  20  by cooling fan  291 , driving force of the engine is inputted into HST input pulley  292  through a transmission element so as to rotate pump shaft  231 .  
         [0095]     Description will now be given of the hydraulic motor  240  arranged on center section  260 .  
         [0096]     As shown in  FIG. 8 , a cylinder block  243  is rotatably and slidably disposed on motor mounting surface  260   m  which is formed at the vertical portion of center section  260 .  
         [0097]     A plurality of pistons  242  are reciprocally movably fitted into a plurality of cylinder bores in cylinder block  243  through respective biasing springs. The heads of pistons  242  abut against a thrust bearing  244   a  of a fixed swash plate  244  which is fixedly sandwiched between upper housing half  246  and lower housing half  247 . An opening  244   b  is provided in the center of fixed swash plate  244  so as to allow motor shaft  241  to pass therethrough.  
         [0098]     In order that motor shaft  241  may function as an output shaft, motor shaft  241  is rotatably supported by a sealed bearing  245  sandwiched between upper housing half  246  and lower housing half  247 , and is not-relatively rotatably engaged with cylinder block  243 , thereby being arranged horizontally on the rotary axis of cylinder block  243 .  
         [0099]     In this way, an axial piston type fixed displacement hydraulic motor is constructed in rear transaxle apparatus  20 .  
         [0100]     Moreover, as shown in  FIG. 8 , the end portion of motor shaft  241  opposite to center section  260  is fitted with a drive output gear  212  in spline fitting such that drive output gear  212  rotates with motor shaft  241 . The portion of motor shaft  241  outward from drive output gear  212  is fitted with a brake rotor  213  in spline fitting. By pressing brake rotor  213  between brake pads  214   a  and  214   b , rotating motor shaft  241  is braked.  
         [0101]     In this embodiment, as mentioned above, brake devices including brake rotor  213  are provided in respective transaxle apparatuses  10  and  20 , although it may be considered that at least one of transaxle apparatuses  10  and  20  is provided therein with the brake device. These two brake devices can be used effectively, namely, one brake device is for braking during running of the vehicle, and the other for a brake at the time of parking. With this structure, a mechanical link interlocked with a running brake pedal and a mechanical link interlocked with a parking brake lever are distributed so as to be simplified. Moreover, the braking effect may be enhanced if both the front and rear brake devices are connected to the running brake pedal so as to be actuated for braking simultaneously.  
         [0102]     As shown in  FIG. 8 , a counter shaft  239  is arranged parallel to motor shaft  241 , a wide, small diameter gear  217  fits loosely on counter shaft  239 , and a large diameter gear  216  is engaged on a toothed side of small diameter gear  217 , thereby constituting a reduction-gear train  215 .  
         [0103]     Regarding reduction-gear train  215 , large diameter gear  216  engages with drive output gear  212 , small diameter gear  217  engages with a ring gear  221  of a differential gear unit  220 , thereby transmitting the driving force from motor shaft  241  to differential gear unit  220  through reduction-gear train  215 .  
         [0104]     Moreover, differential gear unit  220  comprises ring gear  221 , which engages with small diameter gear  217 , pinions  223  rotatably supported by respective pinion shafts  222  which project inward from an inner periphery of ring gear  221 , and left and right side gears  224  fixed to respective rear wheel axles  22 L and  22 R and engaged with each of pinions  223 . Due to this construction, the driving force of motor shaft  241  is transmitted to rear wheel axles  22 L and  22 R through reduction-gear train  215 , ring gear  221 , pinions  223 , and side gears  224 .  
         [0105]     Description will now be given of a hydraulic circuit structure inside of center section  260  and a manifold block  268 , which is attached to the undersurface of center section  260 .  
         [0106]     First, a first embodiment of a hydraulic circuit structure is described. According to the first embodiment, hydraulic motor  40  in front transaxle apparatus  10  and hydraulic motor  240  in rear transaxle apparatus  20  are fluidly connected in series to hydraulic pump in  230 .  
         [0107]     As shown in  FIG. 8 , into pump mounting surface  260   p  in the horizontal portion of center section  260  are bored a first kidney port  261   a  and a second kidney port  261   b  opposite to each other. These kidney ports  261   a  and  261   b  are open at a position above which openings of the cylinder bores of cylinder block  233  pass.  
         [0108]     As shown in  FIG. 10 , into motor mounting surface  260   m  in the vertical portion of center section  260  are bored a first kidney port  262   a  and a second kidney port  262   b  opposite to each other. These kidney ports  262   a  and  262   b  are open at a position where openings of the cylinder bores of cylinder block  243  pass leftward.  
         [0109]     As shown in FIGS.  9  to  11 , in center section  260  are bored an upper first fluid passage  271  and a lower second fluid passage  272  parallel to each other in the longitudinal direction of center section  260 . First fluid passage  271  connects first kidney port  261   a  at pump mounting surface  260   p  to first kidney port  262   a  at motor mounting surface  260   m.  Second fluid passage  272  is connected at the front end thereof to second kidney port  262   b  at motor mounting surface  260   m.    
         [0110]     Moreover, as shown in  FIGS. 9 and 10 , manifold block  268  is attached to the undersurface of center section  260 . In manifold block  268  from a side surface thereof are bored a third fluid passage  273  and a fourth fluid passage  274  parallel to each other and perpendicular to first and second fluid passages  271  and  272 . Into openings of third and fourth fluid passages on the left side surface of manifold block  268  are fitted respective caps  283  and  284  so as to constitute connection ports  273   a  and  274   a . As shown in  FIG. 9 , ends of caps  283  and  284  project outward from lower housing half  247  so as to be connected to hydraulic hoses (not shown) outside of lower housing half  247 . The axes of connection ports  273   a  and  274   a  are disposed in a substantially horizontal plane, namely, they are not slant upward or downward, thereby facilitating the connection work of piping comparatively. That is, the arrangement of connection ports  273   a  and  274   a  in the horizontal plane solves the problems of the reduction of the ground clearance in the case of piping with downward ports and interference of piping with a transmission belt or a frame in the case of piping with upward ports. However, if the minimum requirement is achieved that heads of caps  283  and  284  on the housing of rear transaxle apparatus  20  mounted on the vehicle are prevented from interfering with surrounding instruments, ports  273   a  and  274   a  are accepted to be disposed on any of top, bottom, front, rear, left and right end surfaces of the housing and in any direction.  
         [0111]     Moreover, as shown in  FIG. 9 , between center section  260  and manifold block  268  are bored a vertical fifth fluid passage  275 , which connects second fluid passage  272  to third fluid passage  273 , and a vertical sixth fluid passage  276 , which connects second kidney port  262   b  in pump mounting surface  260   p  to fourth fluid passage  274 .  
         [0112]     Incidentally, a bypass operation lever (not shown) for opening first fluid passage  271  and second fluid passage  272  to the fluid sump is disposed at rear transaxle apparatus  20  in order to enable axles  22 L and  22 R to idle when the vehicle is towed.  
         [0113]     Due to the above-mentioned fluid passages, the hydraulic motor in the front transaxle apparatus  10  and the hydraulic motor  240  in the rear transaxle apparatus  20  are fluidly connected in series to the hydraulic pump  230  in the rear transaxle apparatus  20 .  
         [0114]     That is, as shown in  FIG. 2 , hydraulic hose  81  a connects cap  54   a  on the front transaxle apparatus  10  to cap  283  on rear transaxle apparatus  20 , and hydraulic hose  81   b  connects cap  54   b  on front transaxle apparatus  10  to cap  284  on rear transaxle apparatus  20 , thereby forming a hydraulic circuit shown in  FIG. 12 . The kind of fluid communication means between the front and rear transaxle apparatuses  10  and  20  is not limited. However, like hoses  81   a  and  81   b  according to this embodiment, the means is preferably flexible and resistant to considerably high pressure so as not to interfere with the bending of the vehicle body.  
         [0115]     According to the hydraulic circuit shown in  FIG. 12 , in center section  260  arranged in rear transaxle apparatus  20 , first kidney port  261   a  of pump-mounting-surface  260   p  is connected through first fluid passage  271  to first kidney port  262   a  of motor mounting surface  260   m.  Also, second kidney port  262   b  in center section  260  of motor mounting surface  260   m  is connected to first kidney port  62   a  in center section  62  of front transaxle apparatus  10  to motor mounting surface  63   m  through a string of fluid passages  299   a  which consists of second fluid passage  272 , fifth fluid passage  275 , third fluid passage  273 , hydraulic hose  81   a , and first fluid passage  53   a  provided in center section  62  of front transaxle apparatus  10 .  
         [0116]     Second kidney port  62   b  formed in center section  62  of front transaxle apparatus  10  to is connected to second kidney port  261   b  formed in pump-mounting-surface  260   p  in center section  260  through second fluid passage  53   b  provided in center section  62 , hydraulic hose  81   b , and a string of fluid passages  299   b  which consists of fourth fluid passage  274  and sixth fluid passage  276  in the rear transaxle apparatus  20 .  
         [0117]     As mentioned above, in the hydraulic circuit structure according to the first embodiment, hydraulic motors  40  and  240 , which are arranged in front and rear transaxle apparatuses  10  and  20 , respectively, are fluidly connected in series to hydraulic pump  230 . This in series connection form is suitable for an articulated vehicle in which coupling part  50  serves as a turning center of the vehicle and is arranged at an equidistant position from both the front and rear axles of the vehicle.  
         [0118]     In this way, in front transaxle apparatus  10  and rear transaxle apparatus  20  are driven front wheel axles  12 L and  12 R and rear wheel axles  22 L and  22 R, respectively, thereby realizing a four-wheel-drive vehicle which is excellent in both steering performance and running performance over bad ground conditions.  
         [0119]     Especially, a four-wheel-drive working vehicle provided with the in series hydraulic connection has the capability of freeing its running wheels from mud. For example, even if the vehicle travels in a swamp and a front wheel is stuck in mud, hydraulic fluid discharged from hydraulic pump  230  bypasses hydraulic motor  40  in front transaxle apparatus  10  so as to idle the unloaded front wheels, and then flows into hydraulic motor  240  in rear transaxle apparatus  20  so as to drive the loaded rear wheels, whereby the vehicle can escape from the mud smoothly.  
         [0120]     Alternatively, caps  283  and  284  may be connected mutually through a hydraulic hose bypassing hydraulic motor  40  so as to make a rear-wheel-drive vehicle which drives with only the driving force of hydraulic motor  240  in rear transaxle apparatus.  
         [0121]     When the rotary speed (peripheral speed) of front wheel axles  12 L and  12 R is substantially identical to that of rear wheel axles  22 L and  22 R, hydraulic motors  20  and  240  in respective front and rear transaxle apparatuses  10  and  20  preferably have the same displacement (amount of discharge). With this composition, the same reduction gears may be applicable to both front and rear transaxle apparatuses  10  and  20 . Of course, hydraulic motors of different volume can also be applied in this case, however, the mechanical deceleration ratio of front transaxle apparatus must be different from that of rear transaxle apparatus so as to substantially equalize the rotary speed (peripheral speed) of front wheel axles  12 L and  12 R with that of rear wheels axles  22 L and  22 R.  
         [0122]     In addition, as shown in  FIG. 13 , front transaxle apparatus for driving the front wheels may be modified so that the tilt angle of swash plate  44   c  of hydraulic motor is adjustable and swash plate  44   c  is interlockingly connected to steering wheel  4  through a wire, a link, or similar structure so as to correlate the tilt angle of swash plate  44   c  and the turning angle of steering wheel  4 , thereby increasing the rotary speed of the front wheel axles.  
         [0123]     This structure is particularly effective for improving steering performance of a vehicle having an Ackerman type steering device or a chassis layout wherein a difference of rotary speed is generated between the front wheels and the rear wheels at the time of left or right turning, namely, coupling part  50  is not located equidistant from the front and rear axles of the vehicle.  
         [0124]     Thus, regarding vehicles having the front and rear transaxle apparatuses with a layout wherein a difference of rotary speed is generated between the front wheels and rear wheels at the time of turning, and fluidly connecting in series the hydraulic motors in both the transaxle apparatuses, steering performance can be improved by making the hydraulic motor which actuates steerable wheels (the front wheels) variable in displacement, and increasing the rotary speed of this hydraulic motor in correspondence to the angle of the steering wheel.  
         [0125]     Moreover, in hydraulic circuit shown in  FIGS. 12 and 13 , bypass valves  40   v  and  240   v  are provided to front and rear hydraulic motors  40  and  240 , respectively, so that the fluid passages are opened to the fluid sump by the above-mentioned bypass operation lever, thereby enabling towage of the vehicle. Towing the vehicle can be achieved if at least one of front and rear transaxle apparatuses  10  and  20  is provided with either bypass valve  40   v  or  240   v , respectively. However, according to this embodiment, both front and rear transaxle apparatuses  10  and  20  are provided with respective bypass valves  40   v  and  240   v . Therefore, at the time of assembling, extraction of air can be done from each transaxle apparatus and  20  comparatively easily. Moreover, the vehicle can be towed even in low-temperatures and with high consistency of hydraulic fluid, because hydraulic fluid discharged from each of the idling hydraulic motors  40  and  240  is bypassed near motor  40  or  240  so as not to be considerably resistant to towage of the vehicle.  
         [0126]     Next, description will be given of another embodiment of a hydraulic circuit structure in rear transaxle apparatus  20  according to FIGS.  14  to  17 . The same members or members having the same functions of the above-mentioned embodiment are indicated by the same numerals, and description thereof is omitted.  
         [0127]     As shown in  FIG. 16 , a fluid passage  301  is bored in center section  260  substantially in parallel to fluid passage  271 . As shown in  FIGS. 16 and 17 , one of ends of fluid passage  301  is connected to second kidney port  262   b  opening at motor mounting surface  260   m . As shown in FIGS.  15  to  17 , a substantially vertical hole  301   a  is bored downward from the other end of fluid passage  301  to the lower surface of center section  260 . An L-shaped fluid passage member  302  penetrated by an L-shaped fluid passage is slidably rotatably inserted at its top portion into hole  301   a  through an O-ring so as to connect the L-like passage therein to fluid passage  301  in center section  260 . As shown in  FIGS. 15 and 17 , a cap  303  having an axially penetrating fluid passage is slidably inserted substantially horizontally through an opening  351   a  of a lower housing half  351  into the housing of rear transaxle  20 , and fitted at an inner end thereof into a lower opening of fluid passage member  302  so as to connect the axial fluid passage of cap  303  to the L-shaped fluid passage in fluid passage member  302 . An open outer end of the fluid passage in cap  303  is disposed out of the housing of rear transaxle  20  so as to serve as a connection port  302   a,  to which a pipe connecter  303   a  is fitted for connecting hydraulic hose  81   a  (see  FIG. 13 ) to hydraulic motor  40  in front transaxle  10 .  
         [0128]     On the other hand, as shown in  FIG. 16 , a fluid passage  304  is bored in center section  260  substantially in parallel to fluid passage  271 . As shown in  FIGS. 14, 16  and  17 , a vertically slant fluid passage  305  is bored perpendicularly to fluid passage  304  when viewed in plan. One of ends of fluid passage  305  is connected to second kidney port  261   b  opening at pump-mounting-surface  260   p , and the other end thereof is connected to fluid passage  304 . A substantially horizontal fluid passage  306  is bored perpendicularly to fluid passage  304 , and one of ends of fluid passage  306  is connected to the end of fluid passage  304 . A substantially vertical hole  306   a  is bored from the other end of fluid passage  306  to the lower surface of center section  260 . An L-shaped fluid passage member  307  penetrated by an L-shaped fluid passage is slidably rotatably inserted at a top portion thereof into hole  306   a  through an O-ring. A cap  308  having an axially penetrating fluid passage is slidably inserted substantially horizontally through an opening  351   b  of lower housing half  351  into the housing of rear transaxle  20 , and fitted at an inner end thereof into a lower opening of fluid passage member  307  so as to connect the axial fluid passage of cap  308  to the L-shaped fluid passage in fluid passage member  307 . An open outer end of the fluid passage in cap  308  is disposed out of the housing of rear transaxle  20  so as to serve as a connection port  307   a , to which a pipe connecter  308   a  is fitted for connecting hydraulic hose  81   b  (see  FIG. 13 ) to hydraulic motor  40  in front transaxle  10 .  
         [0129]     Accordingly, first kidney port  261   a  opening at pump mounting surface  260   p  is communicated through fluid passage  271  with first kidney port  262   a  opening at motor mounting surface  260   m . Second kidney port  262   b  opening at motor mounting surface  260   m  is communicated through fluid passages  301  and the fluid passage in fluid passage member  302  with connection port  302   a . Second kidney port  261   b  at pump-mounting-surface  260   p  is communicated through fluid passages  305 ,  304 ,  306  and the fluid passage in fluid passage member  307  with connection port  307   a.    
         [0130]     Therefore, by connecting pipe connecter  303   a  (connection port  302   a ) to hydraulic hose  81   a , and by connecting pipe connecter  308   a  (connection port  307   a ) to hydraulic hose  81   b , hydraulic motor  240  in rear transaxle apparatus  20  and hydraulic motor  40  in front transaxle apparatus  10  are fluidly connected in series to hydraulic pump  230  in rear transaxle apparatus  20 , similarly to the above-mentioned embodiment.  
         [0131]     With regard to the above-mentioned embodiment, manifold block  268  is provided below center section  260 , and a filter  250  is provided below manifold block  268 . However, with regard to the present embodiment, manifold block  268  is not provided, and the fluid passages in fluid passage members  302  and  307  are offset from a filter  350  when viewed in plan. Accordingly, the distance between the lower end of center section  260  and the bottom surface of the lower housing half can be reduced by the thickness of the manifold block, thereby miniaturizing rear transaxle apparatus  20 .  
         [0132]     Furthermore, the fluid passage members  302  and  307  are rotatable against center section  260 , and caps  303  and  308  are slidable against lower housing half  351 , thereby reducing the accuracy of boring holes  301   a ,  306  and  306   a  in center section  260 , and of boring holes  351   a  and  351   b  in lower housing half  351 . Further, the rotation of caps  303  and  308  against lower housing half  351 , or the like, can adjust the directions of pipe connectors  303   a  and  308   a  so as to optimize the piping of hydraulic hoses  81   a  and  81   b.    
         [0133]     Next, description will be given of another embodiment of a hydraulic circuit structure in rear transaxle apparatus  20  shown in  FIG. 18 . In this embodiment, fluid passage member  302  comprises a substantially vertical fluid passage member  302   b  and a substantially horizontal fluid passage member  302   c . Fluid passage member  302   b  is penetrated by a substantially vertical fluid passage. Screw threads are formed on an inner surface of substantially vertical hole  301   a  in center section  260 , and on an outer surface of an upper portion of fluid passage member  302   b,  respectively. The threaded upper portion of fluid passage member  302   b  is screwed into hole  301   a  so as to be connect the substantially vertical fluid passage therein to hole  301   a . Fluid passage member  302   c  is disposed below center section  260 . Fluid passage member  302   c  is bored therein with a substantially horizontal hole having an outwardly opening end into which the inner end of cap  303  is fitted so as to connect the substantially horizontal fluid passage in cap  303  to the substantially horizontal fluid passage in fluid passage member  302   c . A substantially vertical penetrating hole  302   d  is formed in one end portion of fluid passage member  302   c  opposite to cap  303 . A lower end of fluid passage member  302   b  is slidably rotatably inserted through an O-ring into an upper end of hole  302   d.  An open lower end of hole  302   d  is closed with a lid  302   e . Accordingly, an L-shaped passage is formed between hole  301   a  in center section  260  and connecting port  302   a  in cap  303  out of the housing of rear transaxle  20 . The other members are constructed in the same way as the above-mentioned embodiment shown in  FIG. 15 .  
         [0134]     According to this construction, the same effect can be obtained as the above-mentioned embodiment shown in  FIG. 15 . Furthermore, in this embodiment, the members  302   b  and  302   c  constituting fluid passage member  302  can be formed easily. In addition, fluid passage member  307  also can be divisionally constructed similarly to fluid passage member  302  of this embodiment.  
         [0135]     Next, description will be given of another embodiment of a hydraulic circuit structure in rear transaxle apparatus  20  shown in  FIG. 19 . In this embodiment, a downwardly open and substantially vertical fluid passage  310  is bored, and the upper end of fluid passage  310  is connected to kidney port  262   b  opening at motor mounting surface  260   m . A substantially vertically fluid passage member  311  penetrated by a substantially vertical fluid passage is slidably rotatably inserted upward through an O-ring into an opening  352   a  penetrating a bottom surface of a lower housing half  352 , and the upper end of fluid passage member  311  is slidably rotatably fitted into the lower end opening of fluid passage  310  so as to connected the substantially vertical penetrating fluid passage in fluid passage member  311  to fluid passage  310 . A connector  312  is screwed upward into the lower end of fluid passage member  311  below the housing of rear transaxle  20 , so that hydraulic hose  81   a  can be connected to connector  312  so as to fluidly connect kidney port  262   b  of hydraulic motor  240  to hydraulic motor  40  in front transaxle  10 .  
         [0136]     On the other hand, a downwardly open and substantially vertical fluid passage  313  is bored in center section  260 , and the upper end of fluid passage  313  is connected to fluid passage  304  connected to kidney port  261   b  opening at pump mounting surface  260   p  (through fluid passage  305 , as shown in  FIG. 14 ). A substantially vertically fluid passage member  314  penetrated by a substantially vertical fluid passage is slidably rotatably inserted through an O-ring into an opening  352   b  penetrating the bottom surface of lower housing half  352 , and the upper end of fluid passage member  314  is slidably rotatably fitted into the lower end opening of fluid passage  313  so as to connect the substantially vertical fluid passage in fluid passage member  314  to fluid passage  313 . A connector  315  is screwed upward into the lower end of fluid passage member  314  below the housing of rear transaxle  20 , so that hydraulic hose  81   b  can be connected to connector  315  so as to fluidly connect second kidney port  261   b  of hydraulic pump  230  to hydraulic motor  40  in front transaxle  10 . The other members are constructed in the same way as the above-mentioned embodiment shown in  FIG. 16 .  
         [0137]     Due to this structure, as shown in  FIG. 19 , when viewed in plan, the fluid passages in fluid passage members  311  and  314  are offset from filter  350  without manifold block  268 , thereby vertically miniaturizing rear transaxle apparatus  20 . Furthermore, fluid passage members  311  and  314  are used for simply constructing hydraulic ports for fluidly connecting hydraulic pump  230  and motor  240  in rear transaxle  20  to hydraulic motor  40  in front transaxle  10 . Fluid passage members  311  and  314  can be rotated against center section  260  and lower housing half  352  so as to adjust the directions of connectors  312  and  315 , thereby optimizing the piping of hydraulic hoses  81   a  and  81   b .  
         [0138]     Next, description will be given of another embodiment of rear transaxle apparatus  20  having other ports for series connection with hydraulic motor  40  in front transaxle apparatus  10  according to FIGS.  20  to  22 . The same members or members having the same functions of the above-mentioned embodiment are indicated by the same numerals, and description thereof is omitted.  
         [0139]     A center section  560  is detachably secured in the housing of rear transaxle  20  similarly to the above-mentioned center sections. A horizontal pump mounting surface  560   p  and a vertical motor mounting surface  560   m  are formed on center section  560 , a pair of kidney ports  561   a  and  561   b  are opened at pump mounting surface  560   p , and a pair of kidney ports  562   a  and  52   b  are opened at motor mounting surface  560   m.    
         [0140]     A pair of parallel upper and lower fluid holes  571  and  572  are bored in center section  560 , and extended horizontally in the fore-and-aft direction of rear transaxle apparatus  20 . Upper fluid hole  571  is directly opened at an intermediate portion thereof to kidney port  561   a , and at an end thereof to kidney port  562   a.  Lower fluid hole  572  is separated from both kidney ports  562   a  and  562   b  at motor mounting surface  560   m , and opened at one intermediate portion thereof to kidney port  561   b  through a vertically slant hole  573 .  
         [0141]     A center section  560  includes a horizontal flat bottom surface at which fluid holes  574  and  575  are opened downward. Fluid hole  574  is extended vertically downward from another intermediate portion of lower fluid hole  572 , and fluid hole  575  is extended downwardly slantwise from kidney port  562   b,  as best shown in  FIG. 21 . Due to the slanted fluid hole  575 , the bottom opening of fluid hole  575  approaches the bottom opening of fluid hole  574 , thereby minimizing a later-discussed duct block  500  in the fore-and-aft direction of rear transaxle apparatus  20 .  
         [0142]     Duct block  500  is fitted at a horizontal top surface thereof to the bottom surface of center section  560 , and fastened to center section  560  by upwardly screwed vertical bolts  503  and  504 . A pair of vertical holes  500   b  and  500   d  are bored in duct block  500 . Vertical holes  500   b  and  500 d have top ends opened to respective fluid holes  575  and  574  in center section  560 .  
         [0143]     A horizontal hole  500   a  is bored in duct block  500 , and extended laterally from a bottom end of vertical hole  500   b  so as to be opened outward from duct block  500 . A horizontal axial port member  501  is fitted into horizontal hole  500   a  so that a horizontal axial port  501   b  of port member  501  is opened to horizontal hole  500   a . Port member  501  penetrates a wall of the housing of rear transaxle apparatus  20  and is provided with a pipe joint  501   a  at an external end thereof outside rear transaxle apparatus  20 .  
         [0144]     A horizontal hole  500   c  is bored in duct block  500  in parallel to horizontal hole  500   a , and extended laterally from a bottom end of vertical hole  500   d  so as to be opened outward from duct block  500 . A horizontal axial port member  502  is fitted into horizontal hole  500   c  so that a horizontal axial port  502   b  of port member  502  is opened to horizontal hole  500   c.  Port member  502  penetrates a wall of the housing of rear transaxle apparatus  20  and is provided with a pipe joint  502   a  at an external end thereof outside rear transaxle apparatus  20 .  
         [0145]     One of port members  501  and  502  is connected through corresponding pipe joint  501   a  or  502   a  to pipe  81   a  extended from port  54   a , and the other of pipe members  501  and  502  is connected through corresponding pipe joint  502   a  or  501   a  to pipe  81   b  extended from port  54   b , so as to fluidly connect hydraulic pump  230  and hydraulic motor  240  in rear transaxle apparatus  20  to hydraulic motor  40  in front transaxle apparatus  10 . Hydraulic motors  40  and  240  are fluidly connected in series to hydraulic pump  230 .  
         [0146]     Pipe joints  501   a  and  502   a  are rotatable relative to respective port members  501  and  502  fixed to the housing of rear transaxle apparatus  20 , so as to serve as flexible ports to be disposed in suitable directions for connection to pipes  81   a  and  81   b  from ports  54   a  and  54   b.    
         [0147]     While the bottom openings of fluid holes  574  and  575  approach each other as mentioned above so as to ensure the fore-and-aft minimization of duct block  500 , the bottom end of vertical hole  500   c  is lower than the bottom end of vertical hole  500   a  so as to place port member  502  lower than port member  501 , as shown in  FIG. 21 , that is, to vertically offset port member  502  from port member  501 , thereby preventing port members  501  and  502  from interfering with each other.  
         [0148]     Further, when viewed in plan (bottom), as shown in  FIG. 20 , vertical holes  500   b  and  500   d  are substantially aligned in the fore-and-aft direction of rear transaxle apparatus  20 , so as to reduce the lateral offset of fluid hole  575  from fluid holes  571  and  572 , thereby minimizing center section  260  and duct block  500  laterally of rear transaxle apparatus  20 , and simplifying the work for boring the fluid holes in center section  560 .  
         [0149]     Referring to  FIG. 20 , a charge pump  530  is provided on a lower portion of pump shaft  231  projecting downward from center section  560  outside duct block  500 . A fluid filter  535  is clamped between the bottom surface of center section  560  and an upper surface of a bottom wall of the housing of rear transaxle apparatus  20 , so as to enclose charge pump  530 , thereby supplying charge pump  530  with fluid through fluid filter  535  from the fluid sump in the housing of rear transaxle apparatus  20 .  
         [0150]     An outer rotor  532  and an inner rotor  533  are fitted into a pump casing  531  so as to constitute trochoidal charge pump  530 . Inner rotor  533  is fixed on the lower portion of pump shaft  231  projecting downward from center section  560 , so as to be rotatably integral with pump shaft  231 , and relatively rotatably fitted on pump casing  531 . Outer rotor  532  is fixed in pump casing  531  so as to be relatively rotatable to inner rotor  533 .  
         [0151]     As shown in  FIGS. 20 and 21 , a vertical charge fluid hole  576  is bored in center section  560  and opened downward to a delivery port of charge pump  530  between outer and inner rotors  532  and  533 , and opened to upper and lower horizontal fluid holes  571  and  572  through respective upper and lower connection holes  577  and  578 . A charge check valve  521  is fitted in upper fluid hole  571 , and a charge check valve  522  is fitted in lower fluid hole  572 , so as to supply fluid into depressed one of fluid holes  571  and  572 .  
         [0152]     A spring  534  is compressed between pump casing  531  and the upper surface of the bottom portion of the housing of rear transaxle apparatus  20 , so as to slidably press top surfaces of outer and inner rotors  532  and  533  against the bottom surface of center section  560 . When pressure of fluid delivered from charge pump  530  is excessive relative to the force of spring  534 , fluid leaks from the gap between rotors  532  and  533  and center section  560  so as to prevent excessive fluid from entering charge fluid hole  576 . In this way, spring  534  regulates the charge pressure of fluid from charge pump  530  into the HST circuit including hydraulic pump  230  and motors  240  and  40 .  
         [0153]     Referring to  FIGS. 21 and 22 , a horizontal bypass pin  563  is axially slidably fitted in center section  560  in parallel to motor shaft  241 , and faced to cylinder block  242  fitted onto vertical motor mounting surface  560   m  of center section  560 . When a vehicle is to be hauled, bypass pin  563  is moved to project outward from motor mounting surface  560   m , so that cylinder block  242  is pushed by bypass pin  563  and separated from motor mounting surface  560   m , so as to open kidney ports  562   a  and  562   b  to the fluid sump in the housing of rear transaxle apparatus  20 , thereby draining fluid from the HST circuit including hydraulic pump  230  and motors  240  and  40 .  
         [0154]     Description will now be given of a hydraulic circuit structure according to a second embodiment, wherein hydraulic motor  40  in front transaxle apparatus  10  and hydraulic motor  240  in rear transaxle apparatus  20  are fluidly connected in parallel to hydraulic pump  230 .  
         [0155]     As shown in  FIG. 23 , in a horizontal portion of a center section  360  are bored a first kidney port  361   a  and a second kidney port  361   b  opposite to each other. These kidney ports  361   a  and  361   b  are open at a position where openings of the cylinder bores of cylinder block  233  pass.  
         [0156]     On the other hand, as shown in  FIG. 26 , in the vertical portion of the center section  360  are bored a first kidney port  362   a  and a second kidney port  362   b  opposite to each other. These kidney ports  362   a  and  362   b  are open at a position where openings of the cylinder bores of cylinder block  243  pass.  
         [0157]     As shown in  FIGS. 24, 25 , and  27 , in the center section are bored an upper first fluid passage  371  and a lower second fluid passage  372  parallel to each other in the longitudinal direction of center section  360 .  
         [0158]     As shown in  FIG. 24 , in center section  360  is bored a third fluid passage  373  perpendicular to first fluid passage  371  so as to be connected to first fluid passage  371 . An opening of third fluid passage  373  on a side surface of the center section  360  is closed by a plug  373   a.    
         [0159]     As shown in  FIG. 25 , in center section  360  are bored a slant fourth fluid passage  374 , which connects second kidney port  361   b  to second fluid passage  372 . An opening of fourth fluid passage  374  on the side face of center section  360  is closed by a plug  374   a.    
         [0160]     Moreover, as shown in FIGS.  24  to  26 , a manifold block  368  is attached to the undersurface of center section  360 . From a side surface of manifold block  368  are bored a fifth fluid passage  375  and a sixth fluid passage  376  forward and backward parallel to each other and perpendicular to first and second fluid passages  371  and  372 . Caps  385  and  386  are fitted into respective openings of fifth and sixth fluid passages  375  and  376  so as to form respective connection ports  375   a  and  376   a . As shown in  FIGS. 24 and 25 , ends of caps  385  and  386  opposite to manifold block  368  project outward from a lower housing half  347  so as to be connected to hydraulic hoses (not shown) outside lower housing half  347 . Axes of connection ports  375   a  and  376   a  are disposed in a substantially horizontal plane (i.e., a plane which is oriented neither upward nor downward) so as to facilitate piping thereto. However, if the minimum requirement is achieved that heads of caps  385  and  386  on the housing of rear transaxle apparatus  20  mounted on the vehicle are prevented from interfering with surrounding instruments, ports  375   a  and  376   a  are accepted to be disposed on any of top, bottom, front, rear, left and right end surfaces of the housing and in any direction.  
         [0161]     Between center section and manifold block  368  are bored a vertical seventh fluid passage  377  ( FIG. 24 ), which connects a junction point between second and fourth fluid passages  372  and  374  to fifth fluid passage  375 , and a vertical eighth fluid passage  378  ( FIG. 25 ), which connects third fluid passage  373  to sixth fluid passage  376 .  
         [0162]     Due to the above mentioned fluid passage structure, hydraulic motor  40  in front transaxle apparatus  10  and hydraulic motor  240  in rear transaxle apparatus  20  are fluidly connected in parallel to the hydraulic pump  230 .  
         [0163]     That is, as shown in  FIG. 2 , cap  54   a  provided in front transaxle apparatus is connected to cap  385  provided in rear transaxle apparatus  20  through a hydraulic hose  81   a , and cap  54   b  in front transaxle apparatus  10  to the cap  386  in rear transaxle apparatus  20  through a hydraulic hose  81   b , thereby forming a hydraulic circuit shown in  FIG. 28 .  
         [0164]     According to the hydraulic circuit shown in  FIG. 19 , in center section  361   a  arranged in rear transaxle apparatus  20 , the first kidney port  361 , formed to pump mounting surface  360   p , is connected through first fluid passage  371  to first kidney port  362   a  and to motor mounting surface  360   m . First kidney port of  361   a , formed in center section  361   a  to pump mounting surface  360   p , is connected to first kidney port  62   a,  formed to the motor mounting surface  63   m , through a string of fluid passages  399   a , which branch from first fluid passage  371  (as shown in  FIG. 28 ) and consist of third fluid passage  373 , sixth fluid passage  376 , hydraulic hose  81   a , and first fluid passage  53   a  provided in center section  62  of front transaxle apparatus  10 .  
         [0165]     On the other hand, in the center section arranged in the rear transaxle apparatus, the second kidney port  362   b  formed to the motor mounting surface  360   m  is connected to the second kidney port  361   b  formed to the pump mounting surface  360   p  through a string of fluid passage  399   b  which consists of the second fluid passage  372  and fourth fluid passage  374 .  
         [0166]     Moreover, since the fourth fluid passage  374  is connected to the seventh fluid passage  377 , the second kidney port of  361   b  formed to the pump mounting surface  360   p  is connected to the second kidney port  62   b  formed to the motor mounting surface  63   m  through a string of the fluid passage  399   c  which consists of the fourth fluid passage  374 , the seventh fluid passage  377 , and the fifth fluid passage  375  (as shown in  FIG. 28 ), hydraulic hose  81   b , and second fluid passage  53   b  provided in center section  62  of front transaxle apparatus.  
         [0167]     In this way, in the hydraulic circuit structure according to the second embodiment, hydraulic motors  40  and  340  arranged in respective front and rear transaxle apparatuses  10  and  20  are fluidly connected in parallel to hydraulic pump  230 . Particularly, in this parallel connection structure is suitable for a vehicle which turns left and right while generating a difference in rotary speed between the front wheels and the rear wheels.  
         [0168]     Due to the above structure, in front transaxle apparatus and rear transaxle apparatus  10  are driven front wheel axles  12 L and  12 R and rear wheel axles  22 L and  22 R, respectively, thereby making a four-wheel-drive vehicle which excels in steering performance and running performance over bad ground conditions.  
         [0169]     Alternatively, although not shown, caps  385  and  386  may be plugged so as to make a rear-wheel-drive vehicle which drives with only the driving force of hydraulic motor  340  of rear transaxle apparatus  20 .  
         [0170]     Moreover, as shown in  FIG. 28 , the vehicle provided with the in parallel hydraulic connection structure may be modified by providing differential gear units  120  and  220  in front and rear transaxle apparatuses  10  and  20  with respective differential-lock devices  125  and  225  for restricting differential rotation of right and left axles and by providing operation levers for differential-lock devices  125  and  225  on the vehicle, so as to restrict the differential rotation of the axles when any of the running wheels are stuck.  
         [0171]     In the in parallel connection, hydraulic fluid is distributed between the two hydraulic motors  40  and  340 , whereby a larger amount of hydraulic fluid flows to the lighter-loaded of the hydraulic motors  40  and  340 . For this reason, when a right front wheel actuated by hydraulic motor  40  is stuck, for example, the vehicle becomes impossible to free because hydraulic fluid doesn&#39;t flow to hydraulic motor and the rear axles aren&#39;t actuated by operating differential-lock device  125 , load for driving a left front wheel is applied to hydraulic motor  40  so as to supply a suitable amount of hydraulic fluid to rear hydraulic motor  340  so as to drive the rear wheels, thereby enabling the vehicle to be freed.  
         [0172]     Incidentally, in the case where differential-lock devices  125  and  225  are provided to respective front and rear transaxle apparatuses  10  and  20 , a common differential-lock pedal may be provided for both the differential-lock devices so as to actuate the devices simultaneously, or two pedals may be separately provided for the respective differential-lock devices.  
         [0173]     Description will be given of a second embodiment of the working vehicle having rear transaxle apparatus  20 .  
         [0174]     As shown in  FIG. 29 , in the working vehicle according to the second embodiment, a pair of left and right front transaxle apparatuses  400 L and  400 R are provided to front frame  11 . Left and right front transaxle apparatuses  400 L and  400 R include respective front-wheel axles  412 L and  412 R, and are fluidly connected to rear transaxle apparatus  20  through a distribution device  80 , hydraulic hoses, etc.  
         [0175]     As shown in  FIG. 30 , an upper housing half  446  and a lower housing half  447  are joined to each other so as to form a housing of each of front transaxle apparatuses for incorporating a hydraulic motor. Left and right front transaxle apparatuses  400 L and  400 R share the same structure and are supported on front frame  11  through respective stays  19   a  and  19   b  so as to orient front-wheel axles  412 L and  412 R opposite to each other.  
         [0176]     As shown in  FIG. 31 , each of the front transaxle apparatuses  400 L and  400 R incorporates a hydraulic motor  440 , which is fluidly connected to hydraulic pump  230  in rear transaxle apparatus  20  (not shown). Rotation of a motor shaft  441  of hydraulic motor  440  is output to the outside of the housing through each of front wheel axles  412 L and  412 R.  
         [0177]     As shown in  FIG. 31 , into each of front transaxle apparatuses is integrally assembled hydraulic motor  440 , which is so constructed that a cylinder block  443  is rotatably slidably mounted on a motor mounting surface  463   m  formed on a vertical portion of a center section  462 . A plurality of pistons  442  are reciprocally movably fitted into a plurality of cylinder bores in cylinder block  443  through respective biasing springs. The heads of pistons  442  abut against a fixed swash plate  444  which is fixedly sandwiched between upper housing half  446  and lower housing half  447 . An opening  444   b  is provided in the center of fixed swash plate  444  so as to allow motor shaft  441  to pass therethrough.  
         [0178]     So that motor shaft  441  may function as an output shaft, motor shaft  441  is rotatably supported by a sealed bearing  445  which is sandwiched between upper housing half  446  and lower housing half  447 , and is not-relatively rotatably engaged with cylinder block  443  so as to be disposed horizontally on the rotary axis of cylinder block  443 .  
         [0179]     Thus, an axial piston type fixed displacement hydraulic motor is constructed in each of front transaxle apparatuses.  
         [0180]     Moreover, as shown in  FIG. 31 , a pair of first and second kidney ports  462   a  and  462   b  are formed in a vertical portion of center section  462  from a motor mounting surfaces  463   m.  A first fluid passage  453   a  and a second fluid passage  453   b  are horizontally formed in center section  462  so as to be fluidly connected to respective kidney ports  462   a  and  462   b.  First fluid passage  453   a  and second fluid passage  453   b  are connected to respective caps  454   a  and  454   b  to be connected to respective hydraulic hoses. Thus, each of hydraulic motors is fluidly connected to the hydraulic pump  230  in rear transaxle apparatus through the hydraulic hoses (not shown).  
         [0181]     Although not shown, a bypass operation lever for opening first fluid passage  453   a  and second fluid passage  453   b  to the fluid sump is included with each front transaxle apparatuses so as to idle front wheel axles  412 L and  412 R when the vehicle is towed.  
         [0182]     As shown in  FIG. 31 , on an end portion of motor shaft  441  opposite to the center section  462  is provided a drive output gear  431  in spline fitting, whereby drive output gear  431  rotates integrally with motor shaft  441 . On a portion of drive output gear  431  toward center section  462  is integrally formed a brake rotor  433  whose diameter is larger than that of drive output gear  431 , so that rotating motor shaft  441  is braked by pressing brake rotor  433  between brake pads  434   a  and  434   b.    
         [0183]     Moreover, as shown in  FIG. 31 , bearing  439 a and  439 b rotatably support front-wheel axle  412 L (or  412 R) in parallel to motor shaft  441 . A deceleration gear  421  is fixed onto front-wheel axle  412 L (or  412 R) and engages with drive output gear  431 . The diameter of deceleration gear  421  is larger than drive output gear  431  so as to reduce the rotary speed of motor shaft  441  greatly so as to enable each of front transaxle apparatuses to incorporate a hydraulic motor having a small capacity.  
         [0184]     Alternatively, although not shown, instead of front-wheel axle  412 L (or  412 R), upper and lower housing halves  446  and  447  may be formed on a side thereof opposite to the center section  462  with an opening on an axial extension of motor shaft  441 , and motor shaft  441  may be extended through the opening to the outside of the housing so as to be fixed to front wheel  13 . In brief, motor shaft  441  may replace front wheel axle  412 L (or  412 R).  
         [0185]     As shown in  FIG. 29 , front transaxle apparatuses constructed as described above are fluidly connected to rear transaxle apparatus through distribution device  80 , hydraulic hoses, etc., so as to drive respective front-wheel axles  412 L and  412 R, thereby rotating left and right front wheels  13 .  
         [0186]     There are several types of fluidal connection between front transaxle apparatuses  400 L and  400 R and rear transaxle apparatus  20 . These fluidal connection types will be described as follows.  
         [0187]     According to an embodiment shown in  FIG. 32 , employing rear transaxle apparatus according to the first embodiment (shown in FIGS.  8  to  11 ), hydraulic motor  240  of rear transaxle apparatus and a circuit, which fluidly connects in parallel hydraulic motors  440  of both front transaxle apparatuses  400 L and  400 R to each other, are fluidly connected in series to the hydraulic pump of rear transaxle apparatus.  
         [0188]     Due to this structure, front-wheel axles  412 L and  412  of front transaxle apparatuses can be driven differentially.  
         [0189]     According to an embodiment shown in  FIG. 33 , employing a fluidal connection similar to that of  FIG. 32 , both hydraulic motors  440  of front transaxle apparatuses  400 L and  400 R are variable displacement hydraulic motors having respective movable swash plates  444   c . This structure is particularly effective for a vehicle having an Ackerman type steering device or chassis layout wherein a difference in rotary speed is generated between the front wheels and the rear wheels at the time of turning of the vehicle, namely, that coupling part  50  is not located at an equidistant position from both front and rear axles, because a difference of rotary speed can be generated between front and rear wheels by adjusting movable swash plates  444   c  so as to improve steering performance of the vehicle.  
         [0190]     According to an embodiment shown in  FIG. 34 , employing rear transaxle apparatus according to the first embodiment, hydraulic motor  240  of rear transaxle apparatus  20  and hydraulic motors  440  of both front transaxle apparatuses  400 L and  400 R are all fluidly connected in series to hydraulic pump  230  of transaxle apparatus  20 . Moreover, both hydraulic motors  440  of front transaxle apparatuses  400 L and  400 R are variable displacement hydraulic motors having respective movable swash plates  444   c.    
         [0191]     This structure is particularly effective for a vehicle having an Ackerman type steering device or a chassis layout wherein a difference in rotary speed is generated between the front wheels and the rear wheels at the time of turning of the vehicle, namely, that coupling part  50  is not located at an equidistant position from both front and rear axles, because a difference in rotary speed can be generated between front and rear wheels by adjusting movable swash plates  444   c  so as to improve steering performance of the vehicle.  
         [0192]     According to a hydraulic circuit shown in  FIG. 35 , employing rear transaxle apparatus according to the second embodiment (shown in FIGS.  23  to  27 ), hydraulic motor  340  of rear transaxle apparatus  20  and hydraulic motors  440  of both front transaxle apparatuses are all fluidly connected in parallel to hydraulic pump of rear transaxle apparatus.  
         [0193]     Due to this structure, front-wheel axles  412 L and  412  of front transaxle apparatuses can be driven differentially.  
         [0194]     Moreover, the hydraulic circuit in rear transaxle apparatus  20  is fluidly connected to the hydraulic circuit of front transaxle  400 L and  400 R apparatuses through a control valve  80   a . If any of front wheels  13  is stuck, control valve  80   a  stops the supply of hydraulic fluid to front transaxle apparatuses  400 L and  400 R, and hydraulic motor  340  rotates rear wheel axles  22 L and  22 R, whereby the vehicle is freed. Furthermore, differential-lock device  225  is provided to restrict the differential rotation of rear wheel axles  22 L and  22 R so as to correspond to the situation where one of rear wheels  23  is stuck.  
         [0195]     According to an embodiment shown in  FIG. 36 , employing rear transaxle apparatus  20  according to the second embodiment, hydraulic motor  340  of rear transaxle apparatus  20  and a circuit, which fluidly connects in series hydraulic motors  440  of both front transaxle apparatuses  400 L and  400 R to each other, are fluidly connected in parallel to hydraulic pump of rear transaxle apparatus in parallel. Moreover, both hydraulic motors of front transaxle apparatuses  400 L and  400 R are variable displacement hydraulic motors having respective movable swash plates  444   c.    
         [0196]     This structure is particularly effective for a vehicle having an Ackerman type steering device or a chassis layout wherein a difference in rotary speed is generated between the front wheels and the rear wheels at the time of turning of the vehicle, namely, that coupling part  50  is not located at an equidistant position from both front and rear axles, because a difference in rotary speed can be generated between front and rear wheels by adjusting movable swash plates  444   c  so as to improve steering performance of the vehicle.  
         [0197]     Description will now be given of a layout of front transaxle apparatuses.  
         [0198]     As shown in  FIG. 30 , inner ends of front wheel axles  412 L and  412 R, which are opposite to respective front wheels  13 , are inserted in respective front transaxle apparatuses  400 L and  400 R.  
         [0199]     Front transaxle apparatuses are supported on left and right side portions of front frame  11  through stays  19   a  and  19   b,  respectively, so as to ensure a lateral interval  401 L between both front transaxle apparatuses  400 L and  400 R.  
         [0200]     This interval  401 L is wider than a lateral width  402 L of second working-device drive transmission belt  59  at the position where belt  59  passes front transaxle apparatuses.  
         [0201]     With arranging front transaxle apparatuses  400 L and  400 R as described above, even if a working device such as mower device  3  is raised so as to change the vertical height where second working-device drive transmission belt  59  passes, second working-device drive transmission belt  59  interferes with neither front wheel axles  412 L and  412 R nor front transaxle apparatuses. Therefore, the problem of second working-device actuation transmission belt  59  rubbing against front wheel axle  412 L,  412 R, etc., and wearing out is not generated.