Abstract:
A splitter gearbox for a four wheel drive, hydrostatically driven tractor integrates both the input drive train and the output drive train into a single gearbox. The splitter gearbox is mounted to the rear axle housing to allow the sharing of a common oil sump. The front and rear axles of the tractor are driven from a single hydrostatic motor associated with a gear drive system that provides a shaft extending forwardly and rearwardly out of the splitter gearbox to drive, respectively, the front and rear axles of the tractor. An auxiliary pump drive is mounted to the side of the splitter gearbox and driven from an idler gear appropriately positioned within the splitter gearbox.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims domestic priority on U.S. Provisional Patent Application Ser. No. 60/097,463, filed on Aug. 21, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to four wheel drive articulated tractors and, more particularly, to improvements to the drive system for hydrostatically driven tractors. 
     It is desirable to integrate all the drives for the input driven components of an articulated four wheel drive tractor into a single gearbox affixed to the rear axle housing of the tractor. Such a mechanism would place the hydrostatic pump for powering the traction drive of the tractor, the hydraulic pump for the tractor hydraulic system, the drive for the power-takeoff (PTO) system, and any auxiliary hydraulic pumps to be driven off the same gearbox device with the output driver components, including the hydrostatic motor, speed reduction gears and output drive shafts. 
     Lubrication of a gear set is a consideration is the design of a gearbox device for transferring rotational power through gear sets arranged and configured to provide the proper rotational speed to a component driven from the engine of the tractor. Commonizing lubrication sumps can minimize the number of lubrication systems that need to be provided as well as provide more effective lubrication of the gear sets and the cooling of the lubrication fluid. 
     Conventional tractor drive mechanisms include a mechanical transmission to provide different output speeds for a given engine input speed. Even hydraulically driven tractors have utilized a three speed mechanical transmission between the engine and the hydrostatic pump to provide desired different input speeds to the operation of the hydrostatic pump for powering the movement of the tractor. It would be desirable to replace the three speed mechanical transmission on hydrostatically driven tractors to minimize cost and to enhance operation of the tractor. 
     The gearbox would preferably be configured to mount the auxiliary pump drive mechanism in an optional manner so that the auxiliary pump could be added to the gearbox, if desired, and be driven therefrom. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to integrate the drive mechanisms for a hydrostatically driven, four wheel drive tractor in which all the drives are driven from a single splitter gearbox. 
     It is a feature of this invention that the splitter gearbox is affixed to the rear axle housing of the tractor. 
     It is an advantage of this invention that the mounting of the splitter gearbox to the rear axle housing allows the splitter gearbox and the rear axle housing to share a common oil sump. 
     It is another advantage of this invention that the mounting of the splitter gearbox to the rear axle housing reduces complexity. 
     It is another object of this invention to drive the front and rear axles of a four wheel drive tractor from a variable displacement hydrostatic motor. 
     It is another feature of this invention that a hydraulically driven tractor need not have a conventional transmission in order to obtain customary speed ranges desired for a tractor. 
     It is still another feature of this invention that the variable displacement hydrostatic motor can be provided with a selected number of pre-set swash plate positions to effectively replace a conventional transmission gearbox. 
     It is another advantage of this invention that the fixed positions of the variable displacement hydrostatic motor, coupled with a variable speed hydraulic pump, can be controlled electronically to provide a smooth power-shifting operation. 
     It is still another advantage of this invention that the tractor does not require stopping to shift gears in order to change the range of operation of the tractor. 
     It is another feature of this invention that the splitter gearbox incorporates a gear drive system in association with the hydrostatic motor to provide a shaft extending forwardly and rearwardly out of the splitter gearbox to drive, respectively, the front and rear axles of the tractor. 
     It is still another advantage of this invention that the front and rear axles of the four wheel drive tractor are driven from a single hydrostatic motor. 
     It is still another object of this invention that the input drive train and the output drive train arc incorporated into a single splitter gearbox. 
     It is yet another object of this invention to provide an auxiliary pump drive for a four wheel drive tractor. 
     It is still another feature of this invention that the auxiliary pump drive can be mounted as an option to the side of the splitter gearbox. 
     It is yet another advantage of this invention that the auxiliary pump can be driven from an idler gear appropriately positioned within the splitter gearbox. 
     It is a further object of this invention to provide a splitter gearbox for a four wheel drive, hydrostatically driven tractor which is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use. 
     It is still a further object of this invention to provide an auxiliary drive mechanism that can be mounted on a splitter gearbox for a four wheel drive, hydrostatically driven tractor, which is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use. 
     These and other objects, features, and advantages are accomplished according to the instant invention by providing a splitter gearbox for a four wheel drive, hydrostatically driven tractor in which the input drive train and the output drive train are integrated into a single gearbox. The drive mechanism eliminates the need for a separate mechanical gearbox by establishing pre-set fixed displacement settings that are electronically controlled along with the variable displacement of the hydrostatic motor and hydrostatic pump, to provide a smooth power shift through all ranges without requiring the tractor to stop. The drive mechanism is configured so that essentially all components are individually controlled so that the entire power generated by the tractor engine can be diverted to any one of the traction drive, the PTO mechanism, the auxiliary hydraulic drive or, to a somewhat lesser extent, the tractor hydraulic system. The splitter gearbox is mounted to the rear axle housing to allow the sharing of a common oil sump. The input gear set and the output gear set are also within the same common lubrication sump within the splitter gearbox. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages of this invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a side elevational view of a four wheel drive, articulated tractor incorporating the principles of the instant invention, portions of the tractor being broken away for purposes of clarity; 
     FIG. 2 is a schematic side elevational view of the drive mechanism having a splitter gearbox and associated drives incorporating the principles of the instant invention; 
     FIG. 3 is a top plan view of the splitter gearbox and rear axle housing corresponding to lines  3 — 3  of FIG. 2; 
     FIG. 4 is a front elevational view of the splitter gearbox and associated drives corresponding to lines  4 — 4 FIG. 3; 
     FIG. 5 is a rear elevational view of the splitter gearbox corresponding to lines  5 — 5  of FIG. 3; 
     FIG. 6 is a cross-sectional view through the splitter gearbox taken along lines  6 — 6  of FIG. 3; 
     FIG. 7 is a cross-sectional view of the splitter gearbox taken along lines  7 — 7  of FIG. 6 to depict the gear drive system for driving the front and rear axles from a single hydrostatic motor shown in phantom; 
     FIG. 8 is a cross-sectional view of the splitter gearbox similar to that of FIG. 6 to depict the addition of an optional auxiliary pump mechanism; and 
     FIG. 9 is a top plan view of the splitter gearbox and rear axle housing similar to that of FIG. 3 but with an optional auxiliary hydraulic pump mounted to the splitter gearbox. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, a four wheel drive, articulated tractor incorporating the principles of the instant invention can best be seen. The articulated tractor  10  includes a forward engine end  11  supported above the ground G by a front axle assembly  12  and carrying an engine  13 . The rearward cab end  16  of the tractor  10  is supported above the ground by a rear axle assembly  17  and has an operator&#39;s station  18  mounted thereon. Each of the front and rear axle assemblies  12 ,  17  is provided with a pair of opposing wheels  19  for mobile movement of the tractor  10  over the surface of the ground G. The front and rear ends  11 ,  16  of the tractor  10  arc connected by an articulation joint  15 , the manipulation of which effects steering of the tractor  10  in a known manner. 
     As best seen in FIGS. 1-7, the tractor  10  is provided with a drive system  20  that is operatively connected to the engine  13  to provide operative power for the front and rear axle assemblies  12 ,  17 . The drive system  20  includes a splitter gearbox  30  mounted on the front of the rear axle assembly  17  in a manner to share the oil sump therewith for lubrication purposes. The drive system  20  also includes the input drive components, including a hydrostatic pump  22  for powering the traction drive of the tractor  10 , a hydraulic pump  24  for pressuring the hydraulic system of the tractor  10 , and a power takeoff (PTO) mechanism  29 ; and the output drive components, including a variable displacement hydrostatic motor  25  to provide operative power to both the front and rear axle assemblies  12 ,  17  through front and rear output drive shafts  26 ,  27 . 
     The splitter gearbox  30  receives rotational power from the engine  13  via a power input shaft  31  interconnecting the engine  13  and the splitter gearbox  30  to rotate the input gear  32 . As best seen in FIGS. 4-6, the input gear  32  is drivingly engaged with a first idler drive gear  33 , the size of the respective gears  32 ,  33  being selected to provide the appropriately desired gear reduction. The first idler drive gear  33  is drivingly engaged with a pump drive gear  34  having both the hydrostatic pump  22  and the hydraulic pump  24  coaxially mounted therewith, the hydrostatic pump  22  being mounted on the front of the splitter gearbox  30  and the hydraulic pump  24  being mounted on the rear of the splitter gearbox  30 . The idler drive gear  33  is also drivingly engaged with the PTO drive gear  39  for powering the PTO mechanism  29  as a direct drive input from the engine  13 . 
     As best seen in FIGS. 3-7, the hydrostatic pump  22  is operable to circulate hydraulic fluid under pressure to a variable displacement hydraulic motor  25  mounted on the front of the splitter gearbox  30  below the hydrostatic pump  22  to drive rotation of the hydraulic motor  25 . The drive pinion  35  of the hydrostatic motor  25  is drivingly engaged with a second idler gear  36 , which is also appropriately sized to provide the desired gear reduction. The second idler gear  36  is drivingly engaged with a traction driven gear  37  having a single shaft  38  extending therethrough to project both forwardly and rearwardly from the splitter gearbox  30  and form the front and rear output drive shafts  26 ,  27 . Control of the hydrostatic pump is effected through a conventional mechanical linkage. 
     The hydrostatic motor  25  is preferably set-up with three pre-set, fixed swash plate angles to provide three positive displacements for the motor  25  to proximate a conventional operation of the tractor  10 . By utilizing the variable displacement of the hydrostatic motor  25  and/or a variable speed hydrostatic pump  22 , the infinite speed adjustment for the tractor  10  can still be attained on-the-go. Using an electronic control system to control the operation of the motor  25 , such as by modulating the displacement of the motor  25 , and to control the operation of the pump  22 , a very smoothly operating power-shift tractor  10  will result without requiring the operator to stop the tractor to change gears in a mechanical transmission, as is conventional. The fixed, pre-set displacements for the hydrostatic motor  25  provide maximum torque and minimum speed at a first position, a mid-range of both torque and speed at a second position, and a minimum torque with maximum speed for roading operations at a third position. 
     As best seen in FIGS. 1 and 2, the front axle assembly  12  is drivingly connected to the front output drive shaft  26  by a front drive shaft assembly  26   a . The rear axle assembly  17  is drivingly connected to the rear output drive shaft  27  by a rear drive shaft assembly  27   a  passing internally through the housing  28  of the rear axle assembly  17 . Likewise, the PTO mechanism  29  is drivingly connected to the PTO drive gear  39  and passes through the housing  28  of the rear axle assembly  17  and projects rearwardly therefrom for remote connection to an apparatus (not shown) for delivering rotational power thereto. 
     Accordingly, the top portion of the splitter gearbox  30  receives rotational power directly from the engine  13  and drives the input drive train components, including the hydrostatic pump  22 , the hydraulic pump  24  and the PTO mechanism  29 . The lower portion of the splitter gearbox  30  receives operative power from the hydrostatic motor  25  operatively driven from the hydrostatic pump  22  and delivers the rotational power through the output shafts  26 ,  27  to drive the front and rear axle assemblies  12 ,  17  from a single hydrostatic motor  25  off of a single gear drive set  35 - 37 . 
     Referring now to FIGS. 8 and 9, the configuration of the splitter gearbox  30  to receive an optional, auxiliary hydraulic assembly  40 , which includes an auxiliary pump  41 , having a drive pinion  42 , and a rotatably mounted third idler gear  43  drivingly engaged with the drive pinion  42 . The third idler gear  43  projects outwardly from the housing  44  of the auxiliary hydraulic assembly  40  such that the mounting of the housing  44  to the side of the splitter gearbox  30 , as described in greater detail below, will cause the third idler gear  43  to become drivingly engaged with the input gear  32  and, thereby, drive the operation of the auxiliary pump  41 , which can then supplement to operation of the primary hydraulic pump  24 . 
     The process for installing the auxiliary hydraulic assembly  40  is best seen in FIG.  8 . First the removable side cover  45  of the splitter gearbox  30  is detached from the splitter gearbox  30 . The auxiliary hydraulic assembly  40  is then positioned such that the third idler gear  43  extends into the opening in the side of the splitter gearbox  30  formed with the removal of the side cover  45  and becomes engaged with the input gear  32  to receive rotational power directly from the engine  13 , as is the primary hydraulic pump  24 . The housing  44  is then bolted into place on the side of the splitter gearbox and sealed thereto as a replacement for the side cover  45 . 
     The splitter gearbox configuration described above provides a number of different operational configurations for the operator of this hydrstatically driven tractor  10 . By disengaging all other output components, the operator can choose to direct the entire power of the engine  13  to the hydrostatic motor  25  to provide for maximum speed and/or pulling torque of the tractor  10  through one of the pre-set fixed positions of the motor  25 . Alternatively, the operator could disengage the hydrostatic motor  25  by placing its swash plate in a neutral position and run the entire power of the engine  13  through the PTO shaft  29 , while the tractor  10  remains stationary. Another alternative for the operator, would be to disengage both the hydrostatic motor  25  and the PTO mechanism  29 , and run the entire power of the engine  13  through the auxiliary hydraulic system  40 . Yet another alternative for the operator would be to disengage all of the hydrostatic motor  25 , the PTO mechanism  29 , and the auxiliary hydraulic system  40  (if the tractor  10  is so equipped), and divert as much of the power from the engine as possible through the tractor hydraulic system through the hydraulic pump  24 ; however, since both the hydrostatic pump  22  and the hydraulic pump  24  are run from the same gear  34 , less than full engine power can be run through the tractor hydraulics. One skilled in the art will readily recognize that a combination of the above systems will typically be operated, and the operator will have appropriate choices to make for application of the power from the engine  13 . 
     It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention. Accordingly, the following claims are intended to protect the invention broadly as well as in the specific form shown.