Abstract:
A standing lawn mower includes right and left side integrated transaxles for operating the right and left drive wheels independently. The integrated transaxles may include independent hydraulic systems and hydraulic fluid for modularity and reduced risk of cross contamination. The operator support platform is at least partially behind the right and left integrated transaxles.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. 119(e) of the filing date of U.S. Provisional Application No. 61/537960, filed Sep. 22, 2011, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to lawn mowers and more particularly to standing ride-on lawn mowers, and more specifically to a standing ride-on lawn mower having integrated transaxles. 
       SUMMARY 
       [0003]    The invention provides a standing lawn mower comprising: a frame; a right drive wheel supporting the frame; a left drive wheel supporting the frame; a prime mover supported by the frame; a cutting deck assembly supported by the frame for movement between a cutting position in which the cutting deck assembly is lowered with respect to the frame and a travel position in which the cutting deck assembly is raised with respect to the frame, the cutting deck assembly including a cutting deck and at least one cutting blade mounted under the cutting deck and rotating under the influence of the prime mover to cut vegetation when the cutting deck assembly is in the cutting position; a right side integrated transaxle operating under the influence of the prime mover to drive rotation of the right drive wheel independent of the rotation of the left drive wheel, the right side integrated transaxle including a right side housing, a right hydraulic pump within the housing, and a right hydraulic motor within the housing; a left side integrated transaxle operating under the influence of the prime mover to drive rotation of the left drive wheel independent of the rotation of the right drive wheel, the left side integrated transaxle including a left side housing, a left hydraulic pump within the housing, and a left hydraulic motor within the housing; and an operator platform for supporting a standing operator of the lawn mower, the operator platform being positioned at least partially behind the right and left integrated transaxles. 
         [0004]    In some embodiments, the right transaxle includes a right hydraulic system using right hydraulic fluid; and wherein the left transaxle includes a left hydraulic system independent of the right hydraulic system and using left hydraulic fluid that is separate and unmixed with the right hydraulic fluid. In some embodiments, the operator platform is at least partially between the right and left drive wheels. In some embodiments, the prime mover includes a horizontal PTO shaft; the standing lawn mower further comprising a gear box taking as an input torque from the horizontal PTO shaft and delivering as an output a vertical rotating shaft. 
         [0005]    In some embodiments, the prime mover includes a vertical, downwardly extending PTO shaft that defines a vertical PTO axis, the PTO shaft rotating about the PTO axis during operation of the prime mover. In some embodiments, the prime mover includes a PTO bearing supporting the PTO shaft in cantilevered fashion for rotation about the PTO axis; and wherein all portions of both the right side transaxle and the left side transaxle are below a horizontal plane that is below the PTO bearing. In some embodiments, the lawn mower further comprises a power transmission assembly including: a PTO sheave mounted to the PTO shaft for rotation with the PTO shaft about the PTO axis; a right transaxle sheave interconnected with the right hydraulic pump and rotatable to drive operation of the right hydraulic pump; a left transaxle sheave interconnected with the left hydraulic pump and rotatable to drive operation of the left hydraulic pump; an idler; a tensioner; and a belt interconnecting the PTO sheave to the right transaxle sheave, left transaxle sheave, idler, and tensioner to transmit rotation of the PTO sheave under the influence of the PTO shaft into rotation of the right transaxle sheave, left transaxle sheave, idler, and tensioner; wherein each of the right transaxle sheave, left transaxle sheave, idler, and tensioner rotate about an axis of rotation that is parallel to the PTO axis. 
         [0006]    In some embodiments, the operator platform is positioned at least partially behind the right and left drive wheels. In some embodiments, the lawn mower further comprises a hydraulic fluid expansion tank; and wherein the right side integrated transaxle, the left side integrated transaxle, and the hydraulic fluid expansion tank are in fluid communication with each other. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a front perspective view of a lawn mower. 
           [0008]      FIG. 2  is a rear perspective view of the lawn mower. 
           [0009]      FIG. 3  is a perspective view of an operator platform assembly of the lawn mower of  FIG. 1 . 
           [0010]      FIG. 4  is an exploded perspective view of the operator platform assembly. 
           [0011]      FIG. 5  is a section view of the operator platform assembly in an operating position. 
           [0012]      FIG. 6  is a section view of the operator platform assembly in a stored position. 
           [0013]      FIG. 7  is a top view of a portion of the lawn mower. 
           [0014]      FIG. 8  is an exploded rear perspective view of the lawn mower. 
           [0015]      FIG. 9  is an exploded perspective view of a mower drive assembly and drive transmission assembly of the lawn mower. 
           [0016]      FIG. 10  is a schematic view of an integrated transaxle of the mower drive assembly. 
           [0017]      FIG. 11  is a bottom view of the drive transmission assembly. 
       
    
    
       [0018]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
       DETAILED DESCRIPTION 
       [0019]      FIGS. 1 and 2  illustrate a lawn mower  100  embodying the present invention. The lawn mower  100  includes a right front wheel  102 , a left front wheel  104 , a right rear drive wheel  106 , a left rear drive wheel  108 , a frame  110 , an operator platform assembly  112 , a control tower  114 , a mower drive assembly  116 , a cutting deck assembly  118 , a cutting deck transmission assembly  120 , a cutting deck lift assembly  122 , and a height of cut assembly  124 . The figures illustrate a standing ride-on lawn mower  100 , which is a lawn mower on which the operator stands rather than sits. Various features of this mower  100 , including the mower drive assembly  116 , the cutting deck lift assembly  122 , and the height of cut assembly  124  are applicable to other types of lawn mowers, including walk behind lawn mowers and sitting ride-on lawn mowers. 
         [0020]    For the purposes of the present specification, all spatial and directional terms shall, unless specifically stated otherwise, refer to space and direction as perceived by an operator of the lawn mower  100  in the lawn mower&#39;s intended operational orientation, moving over flat, horizontal ground. In ordinary operation, the lawn mower  100  is intended to be oriented with the front and rear wheels  102 ,  104 ,  106 ,  108  in contact with the ground and an operator standing on the operator platform assembly  112  facing toward the front wheels  102 ,  104 . Consequently, the term “forward” and variations thereon shall mean in a direction parallel to the direction from the rear wheels  106 ,  108  toward the front wheels  102 ,  104 . The term “front” and variations thereon shall mean positioned further in the forward direction than an element being compared. The term “reverse” and variations thereon shall mean in a direction parallel to the direction from the front wheels  102 ,  104  toward the rear wheels  106 ,  108 . The term “rear” and variations thereon shall mean positioned further in the reverse direction than an element being compared. The terms “right,” “left,” and variations thereon shall be in reference to the respective right and left as viewed by a forward-looking operator. The terms “up,” “down” and variations thereon shall be used as from the perspective of an operator standing on the operator platform assembly  112 . The terms “above” and “over” shall mean intersecting a comparatively higher horizontal plane, and the terms “directly above” and “directly over” shall mean intersecting a comparatively higher horizontal plane and intersecting a common vertical line. The terms “below” and “under” shall mean intersecting a comparatively lower horizontal plane, and the terms “directly below” and “directly under” shall mean intersecting a comparatively lower horizontal plane and intersecting a common vertical line. Elements that are “directly above” or “directly below” other elements are also “above” or “below” the other elements, but the opposite is not necessarily true. 
         [0021]    The right and left front wheels  102 ,  104  in the illustrated embodiment are of a variety commonly called “caster wheels.” The right and left front wheels  102 ,  104  are passive, meaning that they are not driven under power. The right and left front wheels  102 ,  104  rotate about horizontal axes of rotation. The right and left front wheels  102 ,  104  are mounted to the frame  110  with an arrangement that permits the right and left front wheels  102 ,  104  to swivel with respect to the frame  110  about vertical axes to accommodate turning and rotating of the lawn mower  100 . In some embodiments, the right and left front wheels  102 .  104  are not passive, but instead can be actively steered by the operator. 
         [0022]    The right and left rear drive wheels  106 ,  108  in the illustrated embodiments are driven under the influence of the mower drive assembly  116 , as will be discussed in more detail below. As will be discussed, the right and left rear drive wheels  106 ,  108  in the illustrated embodiment are capable of rotating independent of one another in forward and reverse directions to cause forward, reverse, and turning movement of the lawn mower  100 . The right and left drive wheels  106 ,  108  rotate about a common horizontal axis of rotation  126 . 
         [0023]    When the right and left drive wheels  106 ,  108  rotate in opposite directions (i.e., one forward and one reverse) at the same speed, the lawn mower  100  rotates about a zero-radius turning axis  128 , which may also be referred to as a zero-turn axis or ZT axis. The ZT axis  128  is a vertical axis that intersects the horizontal axis of rotation  126  midway between the right and left rear drive wheels  106 ,  108 . The intersection of the vertical ZT axis  128  and the horizontal axis of rotation  126  may be referred to as the “midpoint” between the right and left rear drive wheels  106 ,  108 . The vertical plane that includes the horizontal axis of rotation  126  and the ZT axis  128  may be referred to as the “reference plane  126 ,  128 .” 
         [0024]    The frame  110  is supported by the right and left front wheels  102 ,  104  and the right and left rear drive wheels  106 ,  108 . The other systems of the lawn mower  100  (i.e., the operator platform assembly  112 , the control tower  114 , the mower drive assembly  116 , the cutting deck assembly  118 , the cutting deck transmission assembly  120 , the cutting deck lift assembly  122 , and the height of cut assembly  124 ) are supported by the frame  110 . 
         [0025]    With reference to  FIGS. 3 and 4 , the operator platform assembly  112  includes an operator platform  130 , a right pivot assembly  132 , a left pivot assembly  134 , a pivot limiting assembly  136 , and a latch assembly  138 . The operator platform assembly  112  is pivotable between an operating position in which it may be said to be “pivoted down” as illustrated in  FIG. 5 , and a stored position in which it may be said to be “pivoted up” as illustrated in  FIG. 6 . Except as specifically noted, the operator platform assembly  112  will be discussed below with reference to its operating position. 
         [0026]    The operator platform  130  includes a plate  140  that has a central flat surface  142  and angled side sections  144 . The operator stands on the operator platform  130  during operation of the lawn mower  100 . For the purposes of the present specification, the term “operator zone” will be used to mean all areas of the lawn mower  100  that are accessible by an operator of the lawn mower  100  standing on the operator platform  130  during ordinary operation of the lawn mower  100 . 
         [0027]    The central flat surface  142  includes slip-resistant features  146 , such as bumps or a rough surface treatment to resist slipping of the operator&#39;s feet. The angled side sections  144  are positioned on the right and left sides of the central flat surface and  142  extend up at angle of between about 10° and 80° with respect to the central flat surface  142 . The angled side sections  144  give the operator tactile feedback as to the operator&#39;s foot position on the operator platform  130 . The operator platform  130  (or, more specifically, the central flat surface  142 ) is pivotable between being generally horizontal when in the operating position ( FIG. 5 ) and generally vertical when in the stored position ( FIG. 6 ). 
         [0028]    The right and left pivot assemblies  132  and  134  are mirror images of each other. Each pivot assembly  132 ,  134  includes an outer bracket  148 , an inner bracket  150 , a pivot sleeve  152 , and a pivot pin  154 . The terms “outer” and “inner” refer to the brackets&#39; positions along the horizontal axis of rotation  126  of the rear drive wheels  106  and  108  with respect to the midpoint between the drive wheels  106  and  108 . The outer bracket  148  is axially further from the midpoint than the inner bracket  150  is. The outer and inner brackets  148 ,  150  include vertical planar sections that are parallel to each other, and in this regard may be characterized as a yoke for the pivot pin  154 . 
         [0029]    The outer bracket  148  is mounted to the side of the frame  110  and extends down between the drive wheel  106 ,  108  and the operator platform  130 . The outer bracket  148  reduces access of the operator&#39;s foot, pants, or other body part or clothing to the rotating drive wheel  106 ,  108  to reduce the likelihood of the operator or the operator&#39;s clothing from coming into contact with the drive wheel  106 ,  108  while the operator is standing on the operator platform  130 . In this regard, the outer bracket  148  may be termed a wheel blocking bracket. The outer bracket  148  includes a pivot pin mounting hole  160 . The inner bracket  150  is also mounted to the frame  110  and extends down. The inner bracket  150  includes a pivot pin mounting hole  162  that aligns with the pivot pin mounting hole  160  in the outer bracket  148 . 
         [0030]    The pivot sleeve  152  includes a through bore  164  and is a cylindrical member rigidly mounted to the operator platform  130 . The pivot sleeve  152  could be made integrally with the operator platform  130  or could be provided separately and rigidly joined or affixed to the operator platform  130 . In the illustrated embodiment, the pivot sleeves  152  are positioned between ears  165  that extend up from the forward ends of the angled side sections  144  of the operator platform  130 . The ears  165  are spaced such that each pair of ears  165  fits between the outer and inner brackets  148 ,  150 . The ears  165  include centering holes  167  that align with the through bore  164 . 
         [0031]    Bushings  169  that have a small diameter portion and a wide flange secure the pivot sleeves  152  to the ears  165 . The small diameter portions of the bushings  169  extend through the centering holes  167  and are press fit into the through bore  164 . The flanges of the bushings  169  sit against the away-facing surfaces of the ears  165 . The flange diameter is larger than the diameter of the centering holes  167 . The bushings  169  include a through bore. 
         [0032]    The pivot pin  154  extends through the pivot pin mounting holes  160 ,  162 , the bushings  167 , and the through bore  164  to pivotally interconnect the operator platform  130  to the outer and inner brackets  148 ,  150  (and thereby to the frame  110 ). A retaining bracket  166 , snap ring, or other means for preventing the pivot pin  154  from axial movement is attached to the pivot pin on the away-facing surface of the inner bracket  150 . The outer end of the pivot pin  154  is secured from axial movement with a nut or other fastener. The pivot sleeves  152  and bushings  169  are free to rotate on the pivot pins  154 , such that the operator platform  130  is pivotable between the operating position and the stored position about the pivot pins  154 . 
         [0033]    The pivot limiting assembly  136  includes a stop plate  168 , a rear cross bar  170 , and a plurality of dampening members  172 . The stop plate  168  is mounted to the front edge of the operator platform  130 , between the inner brackets  150  of the pivot assemblies  132 ,  134 . The stop plate  168  extends at a right angle to the operator platform  130 , and is therefore vertical when the operator platform assembly  112  is in the operating position and horizontal when the operator platform assembly  112  is in the stored position. 
         [0034]    The plurality of dampening members  172  are mounted to the rear facing surface of the stop plate  168 . The dampening members  172  are made of a resilient material such as rubber, to absorb vibrations and shock. 
         [0035]    The rear cross bar  170  is mounted to the rear end of the frame  110 . The dampening members  172  come into contact with the forward-facing side of the rear cross bar  170  when the operator platform assembly  112  is in the operating position. In operation, the weight of the operator is downwardly directed on the operator platform  130 , which causes the operator platform  130  to pivot down on the pivot pins  154 . Downward pivoting of the operator platform  130  is resisted by the dampening members  172  of the stop plate  168  bearing against the rear cross bar  170 . As the lawn mower  100  moves over bumpy terrain, some of the dynamic stresses and vibrations that are transferred to the lawn mower  100  are absorbed by the dampening member  172  to improve the comfort of the operator. Stated another, way, the dampening members  172  provide suspension for the operator standing on the operator platform  130 , which reduces the amplitude of vibration and impact loading that is transmitted to the operator as a result of operating the lawn mower  100 . 
         [0036]    The latching assembly  138  includes a latch pin  174 , a latch arm  176 , and a biasing member  178 . The latch pin  174  is rigidly affixed to the operator platform  130  and extends to one side (the right side in the illustrated embodiment). The latch arm  176  includes a cam surface  180  and a latch slot  182 , and is pivotably mounted to the outer bracket  148  or to another bracket above the outer bracket  148  that is mounted to the frame  110 . The illustrated biasing member  178  is a linearly acting spring, but in other embodiments it may be a torsion spring. The biasing member  178  biases the latch arm  176  toward an engaged position (“down” in the illustrated embodiment). 
         [0037]    Upon pivoting the operator platform  130  into the stored position, the latch pin  174  engages the cam surface  180  of the latch arm  176  and pivots the latch arm  176  against the biasing force of the biasing member  178  (i.e., pivots the latch arm “up” in the illustrated embodiment). Continued movement of the operator platform  130  toward the stored position moves the latch pin  174  into alignment with the latch slot  182 . Upon alignment of the latch pin  174  with the latch slot  182 , the biasing force of the biasing member  178  pivots the latch arm  176  down, such that the latch pin  174  is captured within the latch slot  182 . 
         [0038]    The engagement of the latch pin  174  by the latch arm  176  resists pivotal movement of the operator platform  130  from the stored position toward the operating position. This is often desirable during transportation or storage of the lawn mower  100  because it reduces the overall length of the lawn mower to save space. The operator platform  130  is released from the stored position by lifting the latch arm  176  (e.g., by engagement of one&#39;s finger against the cam surface  180  on the latch arm  176 ) such that the latch pin  174  is free from the latch slot  182  so the operator platform  130  can pivot down toward the operating position. 
         [0039]    The outer bracket  148  of the left pivot assembly  134  includes an arc-shaped slot  183  to accommodate a fastener  447  that pivotably interconnects a slotted arm  424  and a deck lift foot lever  426 , which will be described in greater detail below. 
         [0040]    As illustrated, the operator platform  130  is positioned at least partially behind the right and left rear drive wheels  106  and  108 . The pivot pin  154  is positioned behind and below the common horizontal axis of rotation  126  of the drive wheels  106  and  108 . The entirety of the operator platform  130  is behind the common horizontal axis of rotation  126  of the drive wheels  106  and  108 . In the operating position, the operator platform  130  is below a plane containing the engine deck  210 . 
         [0041]    Referring to  FIG. 7 , the control tower  114  extends vertically from the frame  110  in front of the operator platform  130 . Mounted to a rear-facing side of the control tower  114  is a cushion  184  against which a forward-leaning operator rests during operation of the lawn mower  100 . The control tower  114  includes the following controls, all of which are in the operator zone: an ignition switch  186 , a blade engagement control  188 , a choke  190 , an engine speed control  192 , a right control arm  194 , a left control arm  196 , a reverse hard stop  198 , a forward hard stop  200 , a forward hard stop lock  202 , an interlock  204 , a deck lift hand lever  206 , a height of cut selector  208 , and a height of cut indicator  209 . In the illustrated embodiment, at least some of the controls are located or locatable forward of the reference plane  126 ,  128  (i.e., a plane perpendicular to  FIG. 7  and including the axis of rotation  126 ), but in an alternative preferred embodiment, at least the reverse hard stop  198 , the right control arm  194 , the left control arm  196 , and the forward hard stop  200  are all moved rearward of the reference plane  126 ,  128 . 
         [0042]      FIG. 8  illustrates the mower drive assembly  116 , which includes an engine deck  210 , a fuel source  212 , an engine  214 , a right integrated transaxle  216 , a left integrated transaxle  218 , and a drive transmission assembly  220 . The engine deck  210  is above the operator platform  130  when the operator platform  130  is in the operating position. The engine  214 , acting through the drive transmission assembly  220 , drives a pump in each of the right and left integrated transaxles  216 ,  218 . The engine  214  also drives operation of the cutting deck transmission assembly  120  to cause cutting blades in the cutting deck assembly  118  to rotate and cut grass or other vegetation. 
         [0043]    The right and left control arms  194 ,  196  are interconnect to the right and left integrated transaxles  216 ,  218  to control the speed and direction of rotation of the respective right and left rear drive wheels  106 ,  108 . The right and left control arms  194 ,  196  have a neutral position in which they do not cause any rotation of the right and left rear drive wheels  106 ,  108 . When the right and left control arms  194 ,  196  are pushed forward from the neutral position by the operator, the respective right and left rear drive wheels  106 ,  108  rotate in a forward direction at a speed proportional to the degree of forward movement of the control arms  194 ,  196 . When the right and left control arms  194 ,  196  are pulled rearward from the neutral position by the operator, the respective right and left rear drive wheels  106 ,  108  rotate in a reverse direction (opposite the forward direction) at a speed proportional to the degree of rearward movement of the control arms  194 ,  196 . When one of the control arms is pushed forward and the other is pulled rearward, one of the drive wheels rotates in the forward direction and the other rotates in the reverse direction, giving rise to rotation of the lawn mower  100  about the ZT axis  128 . 
         [0044]    The stop plate  168  of the operator platform assembly  112  moves or passes between the right and left integrated transaxles  216 ,  218  as the foot platform is pivoted between the operating position ( FIG. 5 ) and the stored position ( FIG. 6 ). 
         [0045]    Referring now to  FIG. 7 , the reverse hard stop  198  provides a fixed frame of reference for the operator when manipulating the control levers  194 ,  196 . The operator&#39;s hands and thumbs may rest on the reverse hard stop  198  while the operator&#39;s fingers pull one or both of the control arms  194 ,  196  rearward (i.e., in the reverse direction). Squeezing the control arms  194 ,  196  against the reverse hard stop  198  results in maximum reverse speed for the lawn mower  100 . The operator&#39;s hands are less prone to bouncing or moving unintentionally due to the terrain when the operator&#39;s hands and fingers rest on the reverse hard stop  198 . 
         [0046]    The forward hard stop  200  is adjustable and locked in place by the forward hard stop lock  202 . The forward hard stop  200  may be pivoted forward or rearward into a desired position by disengaging or unlocking the forward hard stop lock  202 , pivoting the forward hard stop  200  to a desired position, and engaging or locking the forward hard stop lock  202 . Once the forward hard stop  200  is set, a desired maximum forward speed has been established for the lawn mower  100 . By squeezing the control arms  194 ,  196  against the forward hard stop  200 , the operator achieves the desired maximum forward speed. When locked in place, the forward hard stop  200  is fixed with respect to the control tower  114  to provide a stable and fixed resting place for the operator&#39;s hands. The operator&#39;s hands and fingers rest on the forward hard stop  200 , while the operator&#39;s thumbs manipulate the control arms  194 ,  196  in the forward direction. The forward hard stop  200  provides a frame of reference for the relative speed being requested of each drive wheel  106 ,  108 . The operator&#39;s hands are less prone to bouncing or moving unintentionally due to the terrain when the operator&#39;s hands and fingers rest on the forward hard stop  200 . 
         [0047]    Referring again to  FIG. 8 , in the illustrated embodiment, the fuel source  212  is a gas tank that contains gasoline for use by the engine  214 . The gas tank can include a primary tank and a back-up tank. The fuel source  212  is mounted to the engine deck  210 . In the illustrated embodiment, the engine  214  is supported by the engine deck  210  and includes a power take off (“PTO”) shaft  238  extending vertically down through the engine deck  210 . The engine  214  also includes a PTO bearing that supports the PTO shaft  238  for rotation about a vertical axis of rotation. Although the illustrated embodiment includes an internal combustion engine  214  and a gasoline tank  212  as the prime mover and fuel source, respectively, other embodiments may include alternative prime movers and suitable fuel sources for such alternative prime movers. Examples of alternative prime movers and fuel sources include a hybrid engine and a source of natural gas or gasoline, an electric motor and batteries, and a fuel cell and hydrogen tank. 
         [0048]      FIGS. 9-11  illustrate the mower drive assembly  116  and drive transmission assembly  220  in more detail. The PTO bearing noted above is visible in  FIG. 9 , and identified with reference number  240 . The PTO bearing  240  supports the PTO shaft  238  for rotation about a vertical PTO axis  242 . The right and left integrated transaxles  216 ,  218  are identical units in the illustrated embodiment. One example of a commercially available and suitable integrated transaxle is manufactured by Hydro-Gear of Sullivan, Ill. 
         [0049]    As schematically illustrated in  FIG. 10 , the integrated transaxles  216 ,  218  include a housing  244  which contains a hydraulic pump  246 , a hydraulic motor  248 , and a dedicated hydraulic loop  250  that includes a reservoir  252 . The hydraulic pump  246  includes an input shaft  254  and the hydraulic motor  248  includes an output shaft  256 . The hydraulic pump  246  also includes a swash plate  258  that can be manipulated to cause hydraulic fluid to flow in forward and reverse directions through the motor  248 . 
         [0050]    In the illustrated embodiment, the right and left integrated transaxles  216 ,  218  are self-contained and do not commingle hydraulic fluid or share a reservoir. The right integrated transaxle  216  includes a right hydraulic system using a right hydraulic fluid, and the left integrated transaxle  218  includes a left hydraulic system using a left hydraulic fluid. The right and left hydraulic fluids are separate and unmixed with each other. This is advantageous over known systems that share hydraulic fluid or components, because the integrated transaxles  216 ,  218  can be separately serviced or replaced and foreign objects or debris in the hydraulic fluid of one of the transaxles will not be shared with the other transaxle. In some embodiments, the integrated transaxles  216 ,  218  can be placed in hydraulic fluid communication to share hydraulic fluid, and in other embodiments, the integrated transaxles  216 ,  218  can share a common reservoir  252 . 
         [0051]    In view of the foregoing, the term “integrated transaxle” may be used to describe a pump, a motor, and a hydraulic system contained within a single housing having a pump input shaft and a motor output shaft extending through the housing such that the integrated transaxle is a modular, self-contained, independent unit. A hydraulic drive system can be constructed by connecting a prime mover capable of delivering an input torque to the pump input shaft of the integrated transaxle and connecting an object to be rotated to the motor output shaft of the integrated transaxle. No additional plumbing, hydraulic components, or other components are required to construct the hydraulic drive system. 
         [0052]    In operation, a linkage connects the right and left control arms  194 ,  196  to the swash plate  258  of the associated integrated transaxle  216 ,  218 . Movement of the control arms  194 ,  196  manipulates the swash plates  258 . The swash plates  258  can be set to a neutral setting (corresponding to the control arm  194 ,  196  being in the neutral position) in which there is substantially no hydraulic fluid flow despite the input shaft  254  rotating. The swash plates  258  can be tilted in forward and reverse directions (corresponding to the control arm  194 ,  196  being moved from neutral in the forward and reverse direction, respectively) in an infinitely adjustable manner to dictate the volumetric flow rate of hydraulic fluid in the selected direction. The motor output shafts  256  rotate in a forward or reverse direction, depending on the direction of flow of the hydraulic fluid from the associated pump  246 . The speed of rotation of the motor output shafts  256  is dictated by the volumetric flow rate of the hydraulic fluid. The output shafts  256  are connected to the associated drive wheels  106 ,  108  to cause rotation of the drive wheels in a forward or reverse direction at a desired speed. 
         [0053]    As illustrated in  FIG. 11 , the drive transmission assembly  220  is mounted directly under the engine deck  210  and includes a drive sheave  262 , a right transaxle sheave  264 , a left transaxle sheave  266 , an idler  268 , a drive tension assembly  270 , and a drive belt  272 . The drive sheave  262  is mounted to the PTO shaft  238  of the engine  214  for rotation with the PTO shaft  238  under the engine deck  210 . The right and left transaxle sheaves  264  and  266  are mounted to the respective right and left transaxle input shafts  254  for rotation with those shafts. The stationary idler  268  is supported for rotation on a shaft that is mounted to the bottom surface of the engine deck  210 . 
         [0054]    The drive tension assembly  270  includes a tension arm  274 , a tensioner  276 , and a spring  278 . The tension arm  274  includes first and second opposite ends. The tension arm  274  is mounted to the engine deck  210  at a pivot point  279  between the first and second opposite ends of the tension arm  274 . One end of the spring  278  is connected to the first end of the tension arm  274 , and the opposite end of the spring  278  is interconnected to the engine deck  210 . The spring  278  is a linear-acting spring, and consequently applies a linear biasing force on the tension arm  274  which biases the tension arm  274  to pivot about the pivot point  279  in a counter-clockwise direction when viewed from below as illustrated by  FIG. 11 . In this regard, the spring  278  can be said to apply a torque biasing force on the tension arm  274  about the pivot point  279 . The tensioner  276  is mounted to the second end of the tension arm  274  and is free to rotate with respect to the tension arm  274 . 
         [0055]    The drive belt  272  interconnects the drive sheave  262 , right transaxle sheave  264 , left transaxle sheave  266 , idler  268 , and tensioner  276 . The drive belt  272  transmits torque from the PTO shaft  238  and drive sheave  262  to the right and left transaxle input shafts  254  to drive operation of the pumps  246  in the transaxles  216  and  218 . The idler  268  and the tensioner  276  ensure that the drive belt  272  contacts each of the sheaves  262 ,  264 , and  266  along an appropriate wrap angle a and that the drive belt  272  is sufficiently tight against the sheaves  262 ,  264 , and  266  to reduce or eliminate slipping of the drive belt  272  with respect to the sheaves  262 ,  264 , and  266 . 
         [0056]    The wrap angle α of the drive belt on the sheaves  262 ,  264 , and  266  is at least 90°. The ratio between the diameter of the drive sheave  262  to the diameter of the right transaxle sheave  264  is preferably 1:1 or close to 1:1. The ratio between the diameter of the drive sheave  262  to the diameter of the left transaxle  266  sheave is preferably 1:1 or close to 1:1. The drive sheave  262 , the right transaxle sheave  264 , the left transaxle sheave  264 , the idler  268 , and the tensioner  276  fit within a rectangular footprint that is less than 4.5 drive sheave diameters by 3.25 drive sheave diameters. The operator platform  130  is at least partially behind the right transaxle  216  and the left transaxle  218 . 
         [0057]    The entire drive transmission assembly  220  is directly under the engine deck  210 . The entire drive transmission assembly  220  is below a horizontal plane that is below the PTO bearing  240 . Examples of such horizontal planes are the planes defined by the top and bottom surfaces of the engine deck  210 . The sheaves  262 ,  264 , and  266 , idler  268 , and tensioner  276  are substantially vertically aligned (i.e., at the same height) so the drive belt  272  is substantially horizontal and is not angled to any significant degree up or down between any of the sheaves  262 ,  264 , and  266 , idler  268 , and tensioner  276 . The input shafts  254  of the right and left transaxles  216  and  218  are vertical and define axes of rotation that are parallel to the PTO axis  242  of the PTO shaft  238 , as are all of the axes of rotation and pivot axes of the sheaves  262 ,  264 , and  266 , idler  268 , tensioner  276 , tension arm  274 , and spring  278 . The output shafts  256  of the right and left transaxles  216  and  218  are horizontal and therefore define axes of rotation that are perpendicular to the PTO axis  242  and the axes of rotation and pivot axes of the other elements of the drive transmission assembly  220 . 
         [0058]    In some embodiments, the prime mover may include a horizontal PTO shaft. In such a configuration, the standing lawn mower may include a gear box taking as an input torque from the horizontal PTO shaft and delivering as an output a vertical rotating shaft that would engage the drive transmission assembly  220  as noted above. 
         [0059]    In operation, the engine  214  drives rotation of the PTO shaft  238  about the PTO axis  242 . The drive sheave  262  is fixed for rotation with the PTO shaft  238 . Rotation of the drive sheave  262  causes linear movement of the drive belt  272 , which causes the right and left transaxle sheaves  266  and  268  to rotate. Tension is maintained in the drive belt  272  with the drive tension assembly  270  and proper wrap angles a are maintained by the positioning of the tensioner  276  and idler  268 . Rotation of the right and left transaxle sheaves  266  and  268  causes rotation of the input shafts  254  of the right and left transaxles  216  and  218 . This drives operation of the hydraulic pump  246  in each of the transaxles  216  and  218 . As the swash plate  258  in the right and left transaxles  216 ,  218  are manipulated (by manipulation of the right and left control arms  194 ,  196 ), hydraulic fluid flows through the motors  248  in the right and left transaxles  218  to drive rotation of the output shaft  256  in a desired direction and at a desired speed, which results in rotation of the right and left drive wheels  106 ,  108  in the desired direction and at the desired speed. 
         [0060]    The right and left drive wheels  106 ,  108  rotate about the horizontal axis  126 , which is collinear with the axes of rotation of the transaxle output shafts  256 . In the event the right and left drive wheels  106 ,  108  are driven in opposite directions of rotation at the same speeds, the lawn mower  100  will rotate about the ZT axis  128 . 
         [0061]    The cutting deck assembly  118  is supported by the frame  110  for movement between a cutting position in which the cutting deck assembly  118  is lowered with respect to the frame  110  and a travel position in which the cutting deck assembly is raised with respect to the frame  110 . The cutting deck assembly  118  includes a cutting deck and at least one cutting blade mounted under the cutting deck and rotating under the influence of the engine  214  to cut vegetation when the cutting deck assembly  118  is in the cutting position. 
         [0062]    The cutting deck lift assembly  122  includes actuators for raising and lowering the cutting deck assembly  118 , and the height-of-cut assembly  124  includes an adjustable mechanism for holding the deck assembly  118  at a desired height during cutting. 
         [0063]    Various features of the invention are set forth in the following claims.