Abstract:
A drive system for a grounds care device using two identical final drives in combination with two identical power units to provide directional drive to the wheels. 
     The final drives and power units are assembled to each other differently for use on each side to provide the required relative reverse rotation of each drive wheel while maintaining the same direction of control movement for forward (or reverse) movement of each drive wheel (in regards to machine movement). 
     Additionally, the drive belt for the cutting unit is routed between the power units (rather than under or over) to allow a lower center of gravity for increased stability.

Description:
This application is a Division of Ser. No. 08/679,195, filed Jul. 12, 1996, now U.S. Pat. No. 5,894,907. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a drive system for wheeled vehicles more particularly, in the preferred embodiment, a commercial ride-on mid-mount deck lawnmower. 
     BACKGROUND OF THE INVENTION 
     Modern ground care equipment, whether they be walk behind or riding, typically have some sort of drive system extending from a source of power like a motor to the drivewheels—typically two in number on opposite lateral sides of a frame. The drive systems are functional in that they do transmit the power to the wheels, thus relieving the operator of the significant chore of physically manipulating the device around the lawn or grounds. The types of transmissions which accomplish this are normally single piece units having a single input drive shaft and a specially designed transmission casing interconnected to both axles—thus to provide the entire drive system in a single package. Other devices, typically in the more expensive commercial units, will have separate drive systems for each side of the device with these special drive systems specifically designed for the certain application. This typically necessitates having a systems specially designed for the right side of the device being distinct from that specially designed for the left side of the device. Alternately, some sort of complex direction or reversing mechanism has to be incorporated into either or both units or to the drive system which interconnects them both commonly to the engine. These special designs are expensive to design, manufacture, and repair. One reason for this is the effective dual inventory and/or high number of complex parts utilized in such systems. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to reduce the cost of a drive system for grounds care equipment. 
     It is another object of the present invention to simplify the construction of drive systems. 
     It is yet another object of the present invention to reduce the physical size of drive systems. 
     It is still another object of the present invention to reduce the complexity of drive systems. 
     It is a further object of the present invention to lower the cost to build and to repair drive systems. 
    
    
     Other objects and a more complete understanding of the invention may be had by referring to the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The structure, operation, and advantages of the presently disclosed preferred embodiment of the invention will become apparent upon consideration of the following description taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a drawing of the main power train for a riding mower incorporating the invention of the application; 
     FIG. 2 is a partially disassembled perspective view of the drive system of FIG. 1; 
     FIG. 3 is a partial cross-sectional view of the left side of the asymmetrical drive system of FIG. 1; 
     FIG. 4 is an end view of the final drive of the main drive system of the device of FIG. 1; and, 
     FIG. 5 is a cross-sectional view of the final drive of FIG. 4 taken substantially along lines  5 — 5  therein. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The transmission of this invention is designed for use with a grounds care device having a frame for controlled travel over a lawn or other grounds. This device may be a riding mower, a walk behind mower, a tractor, a utility vehicle or other device utilized in grounds care. As the particular nature of the device is unnecessary for appreciation of the applicant&#39;s invention, these devices are found in representational form in FIG.  1 . This includes in representation form a frame  4 , an engine  5 , wheels  6 , a driven tool  7  (twin bladed mower with clutch shown), and controls  8  (speed/direction, brake, engine speed and mower shown). The front wheels of the grounds care device are pivotly mounted to the frame  4  so as to allow the device to spin about its rear axles—a zero turn mower. 
     Asymmetrical drive system  10  of this invention includes a final ratio  15  (planetary reduction drive shown), a power unit  50  (a hydrostatic transmission from Agrifab shown), a mounting bracket and skid  70 , and a hydraulic tank  102  as shown in FIG.  2 . 
     The final ratio  15  as shown combines the purposes of providing a speed reduction function in addition to mounting the wheel and power unit onto the frame. 
     The preferred final ratio  15  is mounted in mirror image form as a pair of otherwise identical drives. The invention of the present application includes a way for compensating for the otherwise differing direction rotation of the wheels should this type of drive be connected to a motor rotating in a single direction. The planetary reduction drive  15  itself includes an outer case or housing  16 , a planetary reduction gear system  20 , and an output shaft  40  (FIG.  3 ). 
     The outer case  16  serves to mount the various other elements of the planetary reduction drive  15  together in relation to each other. In the preferred embodiment disclosed, the outer case in addition serves to rotatively mount the wheels  6  to the frame rails  4 , provides a brake, and assists in mounting the later described power unit to the frame. The outer case in addition serves to contain the lubricant for the reduction drive. 
     The planetary reduction system  20  reduces the speed of the later described power unit to that which is more suitable for driving a device across the grounds. The planetary reduction gear system itself includes a spur gear input shaft  21 , an internal gear  22 , a sun gear  24 , a multiplicity of planetary spur gears  25 , and an output carriage assembly  30 . 
     The spur gear input shaft  21  takes the rotary power of the later described power unit and mechanically interconnects it to gear teeth  112  on the inside of the internal gear  22 . In the preferred embodiment disclosed, this provides a substantially 3.643 to 1 speed reduction. 
     The internal gear  22  itself drives a sun gear  24  rotatively mounted to the output shaft  40  by needle bearings  28 . The output carriage assembly  30  is axially aligned with the center of the output shaft  40  surrounding same. A series of four further planetary spur gears  25  are located between the sun gear  24  and a further internal gear  23  fixed to the outer case  16  by pins  26  so as to rotate the output carriage assembly  30  through pins  27 . This interconnects the planetary gear reduction system  20  to the wheels for drivingly interengaging same through an additional 3.3 to 1 reduction ratio. Total reduction is 12.021 to 1 reduction ratio. 
     The output shaft  40  itself is mounted to the outer case  16  of the reduction system by an inner ball bearing  41  and an outer ball bearing  42 . An oil seal  43  immediately adjacent to the outer ball bearing ensures that the lubricant inside the planetary gear reduction system  20  does not escape to the atmosphere. Due to the inclusion of angular loads, the outer ball bearing  42  is preferably larger than the inner ball bearing  41 . 
     The wheel mounting disk  45  with integral lugs  46  on the outside of the planetary gear reduction system allows such system to be selectively interconnected to a wheel. Due to the fact that the planetary reduction drive  15  is itself fixedly interconnected to the frame of the grounds care device (by a bolt to the later described frame interconnect arm and mounting bracket) the bearings  42  and  41  in addition physically support the grounds care device on the wheels—this in addition to the wheel drive previously explained. 
     A brake shaft  32  shown in FIGS. 3-5 enforces brake shoes  33  against the outside diameter of the internal gear  22  (through a cam  31 ) so as to provide for the selective braking of the wheel. 
     A power unit  50  is interconnected to the final ratio in order to provide the rotative power therefor. 
     In the particular preferred embodiment disclosed, this power unit  50  is a BDR drive hydrostatic power unit made by Agrifab and marketed under Model #BDR-301. This hydrostatic power unit  51  has a case  52 . This case  52  serves to contain the movable parts of the hydraulic unit as well as serving to mount the hydrostatic unit onto the outer case  16  of the planetary reduction system  20  (by flange  53 ). The hydrostatic power unit  51  in addition includes a pump input shaft  56 , a motor output shaft  57 , and a direction and speed control  58 . The direction and speed control  58  is accomplished for each power unit  50  using a later to be described control lever also referenced as  58 . 
     The pump input shaft  56  is used to interconnect the hydrostatic unit to a motor. Due to the invention of the particular application, this is easily accomplished by a single drive belt  60  with a single spring loaded idler  65  (see FIG.  1 ). This pump input shaft  56  is typically rotated in a single direction. In the preferred embodiment disclosed, the pump of the hydrostatic unit has an output of 10 ccs per revolution. 
     The motor output shaft  57  provides the output power for the hydrostatic unit  51  (FIG.  3 ). In the preferred embodiment disclosed, this is accomplished by mounting the spur gear input shaft  21  of the planetary reduction system directly on the motor shaft. A boss with an O-ring  54  closely surrounding the motor shaft  57  seals the outer case  16  at this location in order to allow for the hydrostatic unit to be mounted on the planetary gear reduction system in a detachable manner without leaks. 
     Because the motor connected to the output shaft  57  has a capacity of some 21 ccs per revolution output of the output shaft, this hydrostatic unit in addition provides a substantially 2.1 to 1 reduction in speed input to output, thus further serving to increase the torque available for the final ratio  15 . 
     The speed and direction of the motor output shaft  57  of the hydrostatic power unit is under control of a direction and speed control  58 . At the substantially neutral position shown in FIGS.  2 — 3 , the motor output shaft  57  is quiescent. If the speed and direction control  58  is moved angularly clockwise, the output shaft  57  will rotate in one direction, with RPMs increasing upon increasing angular deflection from the neutral position shown. Movement of the direction speed control  58  counterclockwise will cause the motor output shaft to rotate in the other direction, again with RPMs increasing upon increased angular movement of the control  58 . Thus the rotation of the wheel mounting disk  45  is directly under the control of this hydrostatic direction and speed control  58 . 
     A dump valve  59  is preferably located on the hydrostatic transmission so as to allow the wheels to free-wheel. This would allow movement of the grounds care device without operating the engine and/or damaging the components thereof. 
     The particular power unit  50  and final ratios  15  as shown in FIGS. 1 and 2 are asymmetric. This presents both complications and advantages. A tremendous advantage of this asymmetric orientation is that by reorienting the components in respect to each other, power units can be provided for both lateral sides of the grounds care device utilizing the same identical physical components. This substantially halves the inventory requirements for a manufacturer and/or repair dealer while also at the same time paradoxically simplifying the control systems for the device. An example of how this occurs is shown in FIGS. 1 and 2. As shown, by rotating the final drive  15  substantially 180° about a line perpendicular to the output shaft  40 , a substantially mirror image of the final drive  15  is present between the opposite lateral sides of the grounds care device. At the same time this is occurring, the power unit  50 , disconnected from the final drive  15 , is rotated substantially 180° around the pump shaft  56  before being bolted onto the second asymmetric final drive. (note in FIG. 1 that a power unit bulge  63   a  of one power unit  15  points in a rearward direction  127  while a power unit bulge  63   b  of the other power unit  15  points in a forward direction  125 ). In other words, when assembled the final ratios  15  each have wheel connection ends  118   a ,  118   b  facing the respective wheels  6   a ,  6   b  and top sides  120   a ,  120   b  facing in an upward direction  121  and a downward direction  123  respectively, as shown in FIGS. 1-2. The power units  50  when assembled each have ratio connection ends  122   a ,  122   b  facing the respective final ratios  15  and the input shafts  56  each have first ends  124   a ,  124   b  that both face in the upward direction  121  as also shown in FIGS. 1-2. This power unit orientation causes the motors on opposite sides of the device to rotate in opposite directions (the motor on one side rotating clockwise for forward movement of the wheels while the other motor rotates counterclockwise for the same forward movement). 
     With this orientation the reversing of the direction of the power units  50  cancel each other out. By this it is meant that upon movement of the control lever  58  forward on either side of the device that particular wheel drive will power the unit in the same direction. Thus, one power unit  50  receives a clockwise rotation of its control lever  58  and is positioned toward wheel  6   a  thereby causing the wheel  6   a  to rotate to move the device in the forward direction  125  while the other power unit  50  receives a counter clockwise rotation of its control lever  58  and is positioned toward wheel  6   b  thereby causing the wheel  6   b  to rotate to also move the device in the forward Direction  125 . Further, this is accomplished merely by making one of the control rods (control rod  114  being longer as shown) which interconnects the direction and speed control lever  58  to the associated controls approximately 3″ longer at this particular location (control rod  114  being longer as shown)—substantially all other parts of any dual controls can be identical between the two sides. Further, the belt  60  interconnecting the respective power unit  50  to the motor can be short and simple (as shown in FIG. 1) with no concern over the need to compensate for the asymmetric units. 
     A mounting bracket  70  interconnects the power units and final ratio units together so as to (in combination with the later described frame interconnect arm) solidly interconnect the asymmetrical drive system to the grounds care device (FIG.  2 ). 
     The final ratios  15  are bolted separately to the frame interconnect arms  71  by bolts  72  so as to solidly interconnect such final ratio drives to such frame interconnect arms. The final ratios  15  are also separately bolted to the lateral ends of the mounting bracket  70 , by bolts through bolt holes  74  shown in the preferred embodiment. This embodiment is preferred because, due to the displacement of at least one of the holes above the line interconnecting the other two, a strong substantially “L” shaped surface is formed for physically interconnecting the final ratio drives to their mounting bracket. 
     The power units  50 , being fixedly interconnected to the final ratio drive  15 , are reasonably supported thereby. However, to add additional strength, a pump support bracket  75  is bolted to the inner ends of the power units as well as to the central portion of the mounting bracket  70  (at the plane  76 ). This further integrates the power units  50  onto the mounting bracket as well as strengthening the final ratio  15  connection thereto. 
     Note that due to the reversal of mounting of the power units  50  between the lateral sides of the device, the pump support brackets  75  extend at an angle in respect to the mounting bracket  70 . This creates a more solid support surface for the power units  50  at this particular location as well as strengthening the overall rigidity of the mounting bracket. This latter is important because the mounting bracket, one of the lowest elements in the drive system  10 , also serves as a skid-bottoming against the ground in order to protect the drive components from any physical damage. 
     A hydraulic tank weldment  100  completes the construction of the drive system (for clarity shown in represental form in FIG.  2 ). While the specific purpose of this weldment is to localize the hydraulic tank and associated hydraulic components in respect to the power units, it also serves as a physical frame member for the device and more particularly in respect to the operator&#39;s seat and the body of the device in the preferred embodiment. 
     The particular preferred tank weldment  100  disclosed includes two lateral brackets  101 , a hydraulic tank  102 , control mounting flanges  103 , and seat flanges  104 . 
     The two brackets  101  are designed to solidly interconnect the tank weldment  100  to the body of the device. To accomplish this in the preferred embodiment, the two brackets are substantially “C” shaped with downwardly extending flanges  105  for solidly bolting the brackets to the siderails of the frame. To help visualize the “C” shapes, one bracket is referenced  101   a  having two downwardly extending flanges  105   a  and the other bracket is referenced  101   b  having two downwardly extending flanges  105   b.    
     The tank  102  contains the main hydraulic fluid reservoir for the drive system  10 . A single tank  102  is used for both power units  50  in the preferred embodiment. The tank itself is welded to the underside of two straps extending longitudinally between the two brackets  101  to fixedly interconnect the tank  102  thereto. 
     The control mounting flanges  103  provide for a efficient method of mounting engines and machine controls to the frame of the grounds care device. As the particular preferred drive system is used in a ride-on zero turn lawnmower having slightly rounded sides and hinged rear body, the control mounting flanges  103  allow these controls to remain intact on the frame while the hinged rear body is raised. 
     The seat flanges  104  extend upwardly off of the brackets  101  for providing a convenient location for the operator seat. 
     Although the invention has been described in its preferred embodiment with a certain degree of particularity, it is to be understood that numerous changes can be made without deviating from the invention as hereinafter claimed. For example, although the power units disclosed are hydrostatic power units, mechanical units could be substituted without departing with the invention or without multiple speeds. Further differing final drive units could be utilized such as spur gear units, with or without multi-speed ranges. The shift on the fly drive system of U.S. Pat. No. 5,408,896 Power Transmission Drive System, with a multi-speed final ratio would be particularly suitable.