Abstract:
An axle driving apparatus comprises: a common housing; a pair of coaxial axles disposed in the housing; a common input shaft for receiving power from a prime mover, the common input shaft being extended perpendicular to the axles in the housing and passed through a gap between the axles; and a pair of stepless transmissions sharing power from the common input shaft, and transmitting power to the respective axles. The pair of stepless transmissions are arranged in the housing symmetrically centered on an axis of the common input shaft. The axle driving apparatus further comprises: a PTO shaft disposed coaxially to the common input shaft; a clutch disposed in the housing and interposed between the common input shaft and the PTO shaft; and a brake which is applied simultaneously to disengagement of said clutch so as to prevent inertial rotation of said PTO shaft.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. application Ser. No. 10/644,753, filed Aug. 21, 2003, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an axle driving apparatus having a common housing enclosing a pair of hydrostatic transmissions (hereinafter referred to as “HSTs”) and a pair of axles individually driven by the respective HSTs.  
         [0004]     2.Background of the Invention  
         [0005]     Conventionally, as disclosed in Japanese Patent Laid Open Gazette Hei. 7-323739, there is a well-known integrated hydrostatic transaxle (hereinafter referred to as an “IHT”) which is applicable for a snowblower. The IHT comprises a common housing, a pair of HSTs, each of which is a combination of a hydraulic pump and a hydraulic motor, and a pair of coaxial axles individually driven by the respective HSTs, wherein the HSTs and the axles are housed within the housing.  
         [0006]     In the conventional IHT, in order to economically make a common construction between the left and right drive trains from the respective HSTs to the respective axles, the pair of HSTs are disposed laterally symmetrically (in the axial direction of the axles) so as to equalize lateral positions of the HSTs relative to the respective axles (in the axial direction of the axles). However, the pair of HSTs are disposed laterally symmetrically with respect to a vertical line, and the hydraulic pump and hydraulic motor of each HST are juxtaposed laterally in order to vertically downsize the IHT. Consequently, two hydraulic pump and motor pairs are laterally aligned on the substantially same vertical level so that the conventional IHT including the housing is entirely elongated laterally in the axial direction of the axles.  
       SUMMARY OF THE INVENTION  
       [0007]     An object of the present invention is to provide an axle driving apparatus including a common housing incorporating a pair of stepless transmissions and a pair of coaxial axles individually driven by the respective transmissions, wherein the size of the axle driving apparatus in the axial direction of the axles is reduced, while the symmetry of the stepless transmissions in the axial direction of the axles is maintained.  
         [0008]     To achieve the object, an axle driving apparatus comprises: a housing; a pair of coaxial axles disposed in the housing; a common input shaft for receiving power from a prime mover; and a pair of stepless transmissions sharing power from the common input shaft, and transmitting power to the respective axles. The common input shaft is extended perpendicular to the axles in the housing and passed through a gap between the axles. The pair of stepless transmissions are arranged in the housing symmetrically centered on an axis of the common input shaft.  
         [0009]     Therefore, the stepless transmissions are diagonally arranged so as to overlap when viewed perpendicularly to the axles so that the size of the axle driving apparatus including the housing in the axial direction of the axles is reduced, while the symmetry of the stepless transmissions in the axial direction of the axles is maintained. In other words, the equality of positions of the stepless transmissions relative to the respective axles in the axial direction of the drive axles is maintained so that a pair of drive trains from the respective stepless transmissions to the respective axles may share common parts and may have equal operational efficiency.  
         [0010]     Each of the stepless transmissions may be an HST, which includes mutually fluidly connected hydraulic pump and motor. The hydraulic pumps are drivingly connected to the common input shaft, and the hydraulic motors are drivingly connected to the respective axles. Preferably, the hydraulic pump and motor are aligned along each of the axles in the axial direction, whereby the size of the axle driving apparatus including the housing is reduced perpendicularly to the axles, while its expansion in the axial direction of the axles is restrained by the above-mentioned symmetric arrangement of the HSTs centered on the axis of the common input shaft. Further, the common input shaft may be disposed in parallel to rotary axes of the hydraulic pumps, thereby simplifying the driving connection between the input shaft and the HSTs.  
         [0011]     Further, preferably, in each of the HSTs, the hydraulic pump and motor have mutually perpendicular rotary axes. Therefore, even if the hydraulic pump has a rotary axis perpendicular to the axle availably for inputting power from an engine, the hydraulic motor has a rotary axis parallel to the axle so that the hydraulic motor may be drivingly connected to the corresponding axle using inexpensive parts such as spur gears.  
         [0012]     Further, preferably, the axle driving apparatus further comprises: a PTO shaft disposed coaxially to the common input shaft; and a clutch disposed in the housing and interposed between the input shaft and the PTO shaft. Therefore, no drive train, e.g., no gear train, is drivingly interposed between the common input shaft and the PTO shaft, thereby reducing the number of parts, costs, and the size of the axle driving apparatus.  
         [0013]     Further, preferably, the axle driving apparatus further comprises a brake which is applied simultaneously to disengagement of the clutch so as to prevent inertial rotation of the PTO shaft. Thus, the stationary PTO shaft can be easily located to be drivingly connected to a working attachment.  
         [0014]     These, further and other objects, features and advantages will be apparent more fully from the following description. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0015]      FIG. 1  is a left side view of a snowblower equipped with an axle driving apparatus according to a first embodiment of the present invention.  
         [0016]      FIG. 2  is a front view of a mechanism for driving a traveling device and a snow-removing header in the snowblower.  
         [0017]      FIG. 3  is a front view of the axle driving apparatus.  
         [0018]      FIG. 4  is a sectional rear view of the axle driving apparatus.  
         [0019]      FIG. 5  is a sectional plan view of the axle driving apparatus.  
         [0020]      FIG. 6  is a sectional view in the direction of the arrows VI-VI of  FIG. 4 .  
         [0021]      FIG. 7  is a sectional view in the direction of the arrows VII-VII of  FIG. 4 .  
         [0022]      FIG. 8  is a side view of a riding lawn mower equipped with an axle driving apparatus according to a second embodiment of the present invention.  
         [0023]      FIG. 9  is a sectional rear view of the axle driving apparatus according to the second embodiment.  
         [0024]      FIG. 10  is a sectional side view of the axle driving apparatus according to the second embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     A snowblower having an axle driving apparatus of the present invention will now be described with particular reference to  FIG. 1 . Although a snowblower having the axle driving apparatus is described in this embodiment, the axle driving apparatus of the present invention is also applicable to small size vehicles, such as a lawn mower or a small construction machine (including a road maintenance machine).  
         [0026]     A pair of left and right handles  2  are extended upwardly backward from the rear ends of a main frame  1 . A main clutch lever  50 , left and right speed changing levers  3 L and  3 R, and an accelerator lever are disposed between the top portions of handles  2 . An engine  4  is mounted on main frame  1 . A header  5  is disposed in front of main frame  1 . Header  5  comprises a blower case  6  and an auger case  7  which is disposed in front of blower case  6 . A plowing auger  8  having a lateral rotary shaft is arranged in the auger case  7 . A gear box  9  is disposed on the lateral center of the rotary shaft of the plowing auger  8  so as to transfer power from engine  4  to the rotary shaft to thereby drive plowing auger  8 . A chute  10  for discharging snow projects upward from blower case  6 .  
         [0027]     As shown in  FIGS. 1 and 2 , a double output pulley  12  having two front and rear output pulleys  12   a  and  12   b  is disposed on an output shaft  11  of engine  4 . A pulley  14  incorporating a clutch is disposed on a blower shaft  13  extended lengthwise in blower case  6 . Pulley  14  and output pulley  12   a  are bound by a belt  15  so as to drive blower  16  and plowing auger  8  with power of engine  4 .  
         [0028]     Output pulley  12   b  and an input pulley  17  of a later-discussed axle driving apparatus are bound by a belt  18  so as to transmit power from engine  4  to a pair of HSTs in a housing  100  of the axle driving apparatus. In the axle driving apparatus, the pair of HSTs individually drives respective drive axles  35 L and  35 R, shown in  FIG. 2 , at various speeds either forward or rearward.  
         [0029]     A pair of chain casings  36  are disposed on left and right sides of housing  100  of the axle driving apparatus, respectively. Each of chain casings  36  contains a chain transmission interposed between each of drive axles  35 L and  35 R and each of final axles  20 L and  20 R (represented as “ 20 ” in  FIG. 1 ). Left and right drive sprockets  21  are disposed on outer ends of respective final axles  20 L and  20 R. Left and right follower sprockets  22  are journalled by a rear portion of a track frame fixed to the bottom portion of main frame  1 . Left and right crawlers  23  are wound around left sprockets  22  and  23 , so as to constitute a crawler-type traveling device.  
         [0030]     Referring to FIGS.  3  to  7 , a mechanism in the axle driving apparatus of the present invention will now be described. As shown in  FIG. 6 , housing  100  of the axle driving apparatus comprises a front housing part  30 , a middle housing part  31 , and a rear housing part  32 . Three housing parts  30 ,  31  and  32  are mutually joined through respective joint surfaces which are vertically and laterally expanded. As shown in  FIG. 4 , a pair of left and right motor shafts  33 , a pair of left and right counter shafts  34  and the pair of drive axles  35 L and  35 R are laterally extended in parallel in housing  100 . On the joint surface between middle housing part  31  and rear housing part  32  are disposed axes of motor shafts  33  and counter shafts  34 , and middle and rear housing parts  31  and  32  sandwich respective bearings for motor shafts  33  and counter shafts  34 . Drive axles  35 L and  35 R are mutually coaxially arranged in front of the joint surface between middle housing  31  and rear housing  32 , and journalled by left and right side ends of middle housing  31 , respectively.  
         [0031]     As shown in FIGS.  4  to  6 , in a first chamber formed by middle housing part  31  and rear housing part  32 , the pair of HSTs for transmitting power to the respective drive axles  35 L and  35 R are disposed symmetrically centered on a point on the extended longitudinal axis of drive axles  35 L and  35 R in a gap between drive axles  35 L and  35 R. In other words, both the HSTs are arranged diagonally, i.e., laterally and vertically symmetrically so that they are laterally distributed and also vertically distributed oppositely with respect to drive axles  35 L and  35 R. In this embodiment, as shown in  FIG. 4 , the left HST is disposed above left drive axle  35 L, and the right HST below right drive axle  35 R, however, the left and right HSTs may be interchanged in vertical location. Each of the HSTs is constituted by fluidly connecting a hydraulic pump  41  to a hydraulic motor  43  through a center section  40 .  
         [0032]     According to the arrangement of the axle driving apparatus in the illustrated snowblower, input shaft  39  is disposed horizontally so as to locate the right HST under right drive axle  35 R and to expand the portion of housing  100  for the right HST downward. Corresponding to this situation, the pair of chain casings  36  are provided for ensuring sufficient road clearance. If the axle driving apparatus is loaded on a lawn mower having a vertical engine, input shaft  39  is disposed vertically so as to reduce the downward expansion of housing  100 . Therefore, it is unnecessary to provide chain casings  36  for ensuring road clearance, and drive axles  35 L and  35 R may be directly connected at outer ends thereof to respective tires.  
         [0033]     As shown in  FIG. 6 , front housing part  30  and middle housing part  31  constitute a second chamber for housing transmission gears  24 ,  25  and  26 . Pump shafts  45  of the pair of hydraulic pumps  41  project forward, i.e., perpendicularly to drive axles  35 L and  35 R and motor shafts  33 , into the second chamber. In the second chamber, one of pump shafts  45  is provided on the front end thereof with gear  26 . The other pump shaft  45 , provided thereon with gear  24  in the second chamber, projects forward from front housing part  30 , i.e., from the front end of housing  100 , so as to serve as input shaft  39  of both the HSTs. Alternatively, input shaft  39  may be a member separated from pump shaft  45 , or a gear shaft of gear  25  between gears  24  and  26  fixed on respective pump shafts  45  may be projected forward from housing  100  so as to serve as input shaft  39 . Front and middle housing parts  30  and  31  journals a counter shaft  25   a , which is extended lengthwise, i.e., in parallel to pump shafts  45 , and is fixedly provided thereon with gear  25 . Gears  24  and  26  mesh with each other through gear  25  so that both pump shafts  45  are simultaneously driven in the same direction by rotary force inputted to input shaft  39 .  
         [0034]     The first and second chambers of housing  100  are filled with hydraulic oil for the HSTs which is also used as lubricating oil, so as to form an oil sump. As shown in  FIG. 6 , a pipe joint  27  is disposed on an upper portion of housing  100  (rear housing part  32 ). A piping  28  such as a rubber hose is extended from pipe joint  27  and connected to a reservoir tank  29 , which is disposed outside housing  100  as shown in  FIG. 1 , so as to fluidly connect the oil sump to reservoir tank  29 , so that reservoir tank  29  absorbs the excessive volume of hydraulic oil expanded by heat of the HSTs in operation.  
         [0035]     In order to realize the above-mentioned symmetrical arrangement of HSTs centered on point P in the first chamber, as shown in  FIG. 4 , the pair of center sections  40  are disposed laterally and vertically symmetrically centered on point P on the extended axis of drive axles  35 L and  35 R in the gap between drive axles  35 L and  35 R. Each of center sections  40  is L-like shaped when viewed in plan, as shown in  FIG. 5 . On a laterally vertical front surface of center section  40  is formed a pump mounting surface  42  onto which hydraulic pump  41  is mounted. On a longitudinally vertical side surface of center section  40  is formed a motor mounting surface  44  onto which hydraulic motor  43  is mounted. Pump mounting surfaces  42  of the pair of center sections  40  are arranged so as to coincide with the joint surface between middle housing part  31  and rear housing part  32 , thereby concentrating both the HSTs to the approximate middle of housing  100  in the fore-and-aft direction.  
         [0036]     Description will now be given on each of variable displacement hydraulic pumps  41  in accordance with FIGS.  4  to  6 . Each of pump shafts  45  is rotatably supported within center section  40 , and extended forward from center section  40  through the center of pump mounting surface  42 . A cylinder block  46  having a plurality of cylinder bores is rotatably and slidably fitted to each pump mounting surface  42 . Pistons  47  with cooperating and biasing springs are reciprocally inserted into the respective cylinder bores of cylinder block  46 . A pair of movable swash plates  48  are slidably rotatably fitted to a front wall of middle housing part  31 . A thrust bearing of each movable swash plate  48  abuts against heads of pistons  47  of each cylinder block  46 . Each of pump shafts  45  axially penetrates cylinder block  46  and is not relatively rotatably fitted to cylinder block  45 . Further, each pump shaft  45  freely rotatably penetrates movable swash plate  48  while allowing for the rotation of movable swash plate  48 . Consequently, both pump shafts  45  rotatably penetrate the front wall of middle housing part  31  through respective bearings so as to be inserted into the second chamber as mentioned above.  
         [0037]     Each of movable swash plates  48  is individually angularly adjustable with respect to the rotary axis of cylinder block  46  so as to vary the amount and direction of hydraulic oil discharged from each of hydraulic pumps  41 . Movable swash plate  48  has an arcuate convex surface that cooperates with each of arcuate concave surfaces formed in the front wall of middle housing part  31 . Movable swash plate  48  tilted for its angular adjustment is slidably guided along the concave surface of middle housing part  31 .  
         [0038]     As shown in  FIG. 4 , a pair of control shafts  51  for angularly adjusting respective movable swash plates  48  are disposed in parallel to drive axles  35 L and  35 R and arranged laterally and vertically symmetrically centered on point P between drive axles  35 L and  35 R. Control shafts  51  are journalled by middle housing part  31 . One control shaft  51  is disposed at the left end wall of middle housing part  31  above left drive axle  35 L, and the other control shaft  51  is disposed at the right end wall of middle housing part  31  below right drive axle  35 R. A pair of control levers  52  are fixed on outer ends of respective control shafts  51  outside housing  100 . In housing  100 , a pair of swing arms  53  are fixed onto inner ends of respective control shafts  51  and engage at tips thereof into side grooves of respective movable swash plates  48 . When either left or right control lever  52  is rotated either forward or rearward, control shaft  51  and swing arm  53  integrated with rotated control lever  52  are rotated so as to tilt corresponding movable swash plate  48  and change the output of corresponding hydraulic pump  41 .  
         [0039]     Description will now be given of each of hydraulic motors  43  in accordance with  FIGS. 4, 5  and  6 . A cylinder block  57  of each hydraulic motor  43  is slidably rotatably fitted onto motor mounting surface  44  of each center section  40 . A plurality of pistons  58  are reciprocally inserted through biasing springs into a plurality of cylinder bores of cylinder block  57 . Heads of pistons  58  abut against a fixed swash plate  59  immovably sandwiched between middle housing part  31  and rear housing part  32 . Each of motor shafts  33  is axially inserted into cylinder block  57  and not relatively rotatably fitted thereto. Each of motor shafts  33  is extended laterally horizontally, i.e., parallel to each of drive axles  35 L and  35 R from cylinder block  57  and penetrates corresponding swash plate  59  and a corresponding bearing sandwiched between middle and rear housing parts  31  and  32 .  
         [0040]     Description will now be given of each of center sections  40  in accordance with FIGS.  4  to  6 . As shown in  FIG. 4 , center sections  40  are fixed to rear housing part  32  with bolts. Alternatively, center sections  40  may be fastened to middle housing part  31 . Center section  40  is desirably removable from housing  100 .  
         [0041]     On pump mounting surface  42  of each center section  40  are disposed a pair of arcuate ports around pump shaft  45  in fluid communication with the cylinder bores in cylinder block  46  of hydraulic pump  41 . On motor mounting surface  44  of each center section  40  are disposed a pair of arcuate ports around motor shaft  33  in fluid communication with the cylinder bores in cylinder block  57  of hydraulic motor  43 . As shown in  FIG. 6 , within each center section  40 , an upper oil passage  40   a  and a lower oil passage  40   b  are bored so as to connect the respective arcuate ports on pump mounting surface  42  to the respective arcuate ports on motor mounting surface  44 , thereby constituting a closed hydraulic circuit for mutually fluidly connecting hydraulic pump  41  and motor  43 .  
         [0042]     Check valves  61  and  62  are fitted forward into each center section  40  so as to be connected to respective oil passages  40   a  and  40   b . A horizontally cylindrical oil filter  63  is interposed between rear housing part  32  and the rear end surface of each center section  40  so as to cover check valves  61  and  62 . Therefore, hydraulic oil in housing  100  is filtrated by each oil filter  63  and supplied into oil passage  40   a  through check valve  61 , or into oil passage  40   b  through check valve  62 .  
         [0043]     As shown in  FIGS. 5 and 6 , a pair of oil release members  64  are disposed behind respective center sections  40  and supported by the rear wall of rear housing part  32 . When the snowblower with engine  4  shut down is hauled, each of oil relief members  64  is manually operated from the outside of housing  100  so as to forcibly open check valves  61  and  62  and release oil from oil passages  40   a  and  40   b  to the oil sump in housing  100 . Due to this oil pressure relief, in each of the HSTs, hydraulic motor  43  interlocking with corresponding axle  35 L or  35 R and  20  becomes free from the fluid connection with hydraulic pump  41 , so that corresponding drive sprocket  21  is freely rotated according to the hauling of the snowblower and hydraulic pump  41  is prevented from receiving back flow of hydraulic oil caused by rotation of hydraulic motor  43 , thereby protecting the HST and engine  4 .  
         [0044]     Description will now be given of the gear train from each motor shaft  33  to each of drive axles  35 L and  35 R in accordance with  FIGS. 4, 5  and  7 . As shown in  FIG. 4 , each of counter shafts  34  parallel to motor shaft  33  and drive axle  35 L or  35 R is disposed between motor shaft  33  and corresponding drive axle  35 L or  35 R in rear (front) view as shown in  FIG. 4 , and aligned with motor shaft  33  in a vertical row in side view as shown in  FIG. 7 . Each of motor shafts  33  projects from the above-mentioned bearing and is sandwiched between middle and rear housing parts  31  and  32  opposite to fixed swash plate  59 . This projecting portion of motor shaft  33  is peripherally formed into a gear  65 , which meshes with a diametrically larger gear  67  fixed on counter shaft  34 . Counter shaft  34  is peripherally formed with a gear  68 , which meshes with a diametrically larger gear  69  fixed on each of drive axles  35 L and  35 R. In this way, between motor shaft  33  and corresponding drive axle  35 L or  35 R is constructed a reduction gear train including gears  65 ,  67 ,  68  and  69 .  
         [0045]     Description will now be given on a pair of locking mechanisms provided for the respective drive trains for the drive axles  35 L and  35 R so as to constitute a parking brake system of the snowblower, in accordance with FIGS.  3  to  5  and  7 . More specifically, each of the locking mechanisms directly locks corresponding motor shaft  33  so as to lock the corresponding drive train from motor shaft  33  to crawler  23 . As shown in  FIGS. 4 and 5 , each motor shaft  33  is fixedly provided on the tip thereof with a locking disk  66 . Each locking disk  66  is provided on the peripheral edge thereof with a plurality of (in this embodiment, four) detent notches  66   a , as shown in  FIG. 7 . On the other hand, as shown in  FIGS. 5 and 7 , a pair of locking shafts  71  are longitudinally slidably supported by middle housing part  31  through respective bushes  75  in perpendicular to respective motor shafts  33 . The rear end of each locking shaft  71 , when sliding rearward, enters any of detent notches  66   a  of each locking disk  66 .  
         [0046]     Locking shafts  71  projects outwardly forward from housing  100  (middle housing part  31 ) so as to be diametrically penetrated by an engaging pin  72 . A pair of locking levers  74  are pivotally supported at the intermediate portions thereof by front end portions of middle housing part  31  through respective pivotal pins  73 . Each engaging pin  72  is passed through a notch  74   a  formed at the bottom end of each locking lever  74  so as to pivotally connect locking lever  74  to locking shaft  71 . By forwardly rotating the top end of each locking lever  74 , the bottom end of locking lever  74  below pivotal pin  73  is rotated rearward so that locking shaft  71  slides rearward and enters one of detent notches  66   a , thereby locking motor shaft  33  through locking disk  66 . Therefore, the corresponding left or right drive system from motor shaft  33  to crawler  23  is kept stationary.  
         [0047]     As shown in  FIG. 3 , the pair of locking levers  74  are arranged in a space in front part of middle housing part  31  on upper left side and lower right side of front housing part  30  containing transmission gears  24 ,  25  and  26 , thereby being prevented from interfering with another lever or link. Locking levers  74  are connected to each other through a link (not shown) and to a single parking brake lever (not shown). By manipulating the parking lever, both of locking levers  74  are moved thereby locking the left and right drive systems simultaneously.  
         [0048]     As shown in  FIG. 2 , the left traveling drive system from left drive axle  35 L and left crawler  23  through left chain casing  36  and the right traveling drive system from right drive axle  35 R and right crawler  23  through right chain casing  36  are laterally symmetric with housing  100  therebetween. In housing  100 , the left drive train from the left HST to left drive axle  35 L and the right drive train from the right drive train to right drive axle  35 R are symmetric centered on point P between drive axles  35 L and  35 R on the axis thereof so that, as understood from  FIG. 4 , the HST for left drive axle  35 L and the HST for right drive axle  35 R overlap laterally when viewed in plan. Accordingly, the whole of axle driving apparatus including housing  100  is narrowed laterally.  
         [0049]     For the snowblower shown in  FIG. 1 , the described axle driving apparatus is applied in the state that input shaft  39  projects forward, i.e., the left and right HSTs are vertically distributed with drive axles  35 L and  35 R therebetween. Alternatively, when the axle driving apparatus is used for a lawn mower having a vertical crankshaft engine, it may be arranged so as to orient input shaft  39  vertically. In this case, the left and right HSTs come to be distributed in front and rear of drive axles  35 L and  35 R.  
         [0050]     Further, the axle driving apparatus may be applied for constituting a wheel type traveling device by directly attaching grounding wheels onto respective drive axles  35 L and  35 R, as well as the crawler traveling device as shown in  FIGS. 1 and 2 .  
         [0051]     An alternative axle driving apparatus  101  will be described with reference to FIGS.  8  to  10 . Axle driving apparatus  101  has a PTO shaft  127  and an input shaft  125  which are coaxially oppositely extended forward and rearward from a housing of axle driving apparatus  101 .  
         [0052]      FIG. 8  illustrates a riding lawn mower  200  serving as an example of a working vehicle equipped with axle driving apparatus  101 . Riding lawn mower  200  has a chassis  201 . A carrier  208  is (or carriers  208  are) supported on a front end portion of chassis  201 . Axle driving apparatus  101  is disposed at a longitudinal middle portion of riding lawn mower  200  between left and right side frame portions of chassis  201 . Left and right drive axles  35 L and  35 R project leftward and rightward from the housing of axle driving apparatus  101 , and penetrate the left and right side frame portions of chassis  201  so as to be connected at distal ends thereof to respective left and right drive wheels  210 .  
         [0053]     The housing of axle driving apparatus  101  is constituted by mutually joined front, middle and rear housing parts  32 ,  31  and  30 , similar to the housing of axle driving apparatus  100 . To fix the housing to chassis  201 , as shown in  FIGS. 8 and 9 , middle housing part  31  is integrally formed with left and right extended boss portions  31   a  supporting respective drive axles  35 L and  35 R, and outer ends of boss portions  31   a  are fastened to the left and right side frame portions of chassis  201 . As shown in  FIG. 9 , vertical penetrating bolt holes  31   b  are formed in the outer ends of boss portions  31   a  so as to be used for fastening the outer ends of boss portions  31   a  to the left and right side frame portions of chassis  201  with bolts.  
         [0054]     As shown in  FIG. 8 , riding lawn mower  200  has a body cover  207  enclosing chassis  201 . An operator&#39;s seat  203  is mounted on body cover  207  just above axle driving apparatus  101 . A pair of left and right speed changing levers  202  (only one of them is illustrated in  FIG. 8 ) are extended upright from body cover  207  just in front of seat  203 , and operatively connected through respective link rods  49  to respective left and right control levers  52  pivoted on the housing of axle driving apparatus  101 . Control levers  52  interlock with respective movable swash plates  48  of hydraulic pumps  41  in the housing of axle driving apparatus  101 .  
         [0055]     An engine  204  is supported by chassis  201  via vibratory isolating supporters  204   c  behind axle driving apparatus  101 . A radiator  205  is disposed behind engine  204 . Engine  204  has a front flywheel  204   a  serving as an output terminal. A clutch shaft  130  projects forward from flywheel  204   a , and is drivingly connected to flywheel  204   a  via a clutch  204   b . Input shaft  125  of axle driving apparatus  101  projects rearward from the housing of axle driving apparatus  101 , and is drivingly connected to clutch shaft  130  via a propeller shaft  129  and universal joints, thereby receiving power from engine  204 .  
         [0056]     A mower unit  209  containing a rotary mowing blade is suspended downward from chassis  201  between carrier (carriers)  208  and axle driving apparatus  101 . PTO shaft  127  of axle driving apparatus  101  projects forward from the housing of axle driving apparatus  101 , and is drivingly connected to an input shaft  209   a  of mower unit  209  via a propeller shaft  128  and universal joints so as to drive the rotary mowing blade in mower unit  209 .  
         [0057]     Referring to  FIGS. 9 and 10 , similar to axle driving apparatus  100 , axle driving apparatus  101  has HSTs disposed symmetrically centered on the center point in a gap between drive axles  35 L and  35 R in the housing. Each of the HSTs comprises mutually fluidly connected hydraulic pump  41  and hydraulic motor  43 , which are aligned in the axis direction of drive axles  35 L and  35 R. In each of the HSTs, axial motor shaft  33  of hydraulic motor  43  is disposed perpendicular to axial pump shaft  45  of hydraulic pump  41 , and disposed in parallel to each of drive axles  35 L and  35 R so as to be drivingly connected via the gear train to corresponding drive axle  35 L or  35 R. In comparison with  FIGS. 4 and 6 , the same reference numerals designate the same members and portions, which have the same functions. Description of the same members and portions are omitted.  
         [0058]     Input shaft  125  serves as a rotary shaft of gear  25  disposed between gears  24  and  26  so as to distribute the input power between hydraulic pumps  41 . In this regard, similar to lower hydraulic pump  41 , upper hydraulic pump  41  also has pump shaft  45  which does not project outward from the housing of axle driving apparatus  101 . Gear  24  is fixed on pump shaft  45  of upper hydraulic pump  41  and meshes with gear  25 .  
         [0059]     Input shaft  125  is extended forward in the housing and passed through the gap between proximal ends of drive axles  35 L and  35 R. Thus, the HSTs are symmetric centered on an axis of input shaft  125 . A front center portion of front housing part  32  projects forward so as to form a PTO housing portion  32   a  incorporating a PTO clutch-and-brake unit  126 , which may be hydraulically or electromagnetically controlled. A front end of input shaft  125  enters PTO housing portion  32   a , and is connected to PTO clutch-and-brake unit  126 . PTO shaft  127  projecting forward from PTO housing portion  32   a  is connected at a rear end thereof to PTO clutch-and-brake unit  126 . PTO clutch-and-brake unit  126  has a clutch which is disengaged to isolate PTO shaft  127  from the rotary force of input shaft  125 . PTO clutch-and-brake unit  126  has a brake which is applied simultaneously to the disengagement of the clutch, thereby preventing inertial rotation of PTO shaft  127 .  
         [0060]     Although the present invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been changed in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.