Abstract:
A vent tube for a splitter gearbox mounted on the rear axle assembly of a four-wheel drive tractor. The vent tube extends into the rear axle assembly, while in fluid flow communication with the lubricating oil in the splitter gearbox, and either breaks a vacuum at a balance hole or permits oil transfer from the splitter gearbox, depending upon which direction the output gears are being driven. The output gears turn at high rpm and cause churning of the oil. The vent tube assembly relieves this condition and thereby significantly reduces parasitic power losses.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to splitter gearboxes used in four-wheel drive agricultural tractors, and more particularly to a vent tube to improve the performance, reliability and durability of such gearboxes. 
     An integrated splitter gearbox for four-wheel drive tractors is shown and claimed in U.S. Pat. No. 6,230,830 which is incorporated herein fully by reference. Therein is discussed the desirability of integrating 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. The instant invention is an improvement to a splitter gearbox as generally disclosed in the &#39;830 patent. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to provide a vent tube that significantly reduces parasitic losses due to the churning of oil by the output gears of a splitter gearbox. 
     Another object of the present invention is to provide a novel means for reducing parasitic losses in a splitter gearbox. 
     It is another object of the instant invention to provide a splitter gearbox with improved operational characteristics and specifications. 
     Yet another object of the present invention is to provide a vent tube and a non-spring operated poppet check valve assembly that reduces the parasitic losses in a splitter gearbox. 
     It is yet another object of this invention to provide an improved 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 a still further object of the instant invention to provide a vent tube for a splitter gearbox mounted on the rear axle assembly of a four-wheel drive tractor. The vent tube extends into the rear axle assembly, while in fluid flow communication with the lubricating oil in the splitter gearbox, and either breaks a vacuum at a balance hole or permits oil transfer from the splitter gearbox, depending upon which direction the output gears are being driven. The output gears turn at high rpm and cause churning of the oil. The vent tube assembly relieves this condition and thereby significantly reduces parasitic power losses. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The advantages of this invention will be 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  of FIG. 3; 
     FIG. 5 is a side elevational view of the splitter gearbox, showing clearly the vent tube assembly, corresponding to lines  5 — 5  of FIG.  3 ; 
    
    
     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 axles assemblies  12  and  17  is provided with a pair of opposing wheels  19  for mobile movement of the tractor  10  over the surface of the ground G. An articulation joint  15 , the manipulation of which effects steering of the tractor  10  in a known manner, connects the front and rear ends  11  and  16  of the tractor  10 . 
     As best seen in FIGS. 1-5, 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 real axle assemblies  12  and  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  and  17  through front and rear output drive shafts  26  and  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 and 5, the input gear  32  is drivingly engaged with a first idler drive gear  33 , the size of the respective gears  32  and  33  being selected to provide the appropriately desire gear reduction. The first idler drive gear  33  is drivingly engaged with a pump drive gear  34  having both the hydrostatic pump  22  and 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 FIG. 3, 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 from the front and rear output drive shafts  26  and  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  and  27  to drive the front and rear axle assemblies  12  and  17  from a single hydrostatic motor  25  off of a single gear drive set  35 - 37 . 
     Referring to FIG. 5, the interface between the rear axle housing  28  and the splitter gearbox  30  can be seen to include a faceplate  50  that, except as described and discussed further below, closes the entire opening  51  between the two. Shafts  29  and  38  extend through faceplate  50  and rotate relative thereto as required in the operation of tractor  10 . A balance hole  54  extends through faceplate  50  at the lower portion thereof to help balance the lubricating oil levels in the splitter gearbox  30  and axle housing  28 . 
     Vent tube assembly  58  can best be seen in FIG. 5 as comprising an elongate tube  59  with a flange  61  sealingly affixed to faceplate  50  by bolts  62  over balance hole  54 . At the rearward end of the tube  59  is a one-way valve  64  that permits flow only in the direction away from gearbox  30 , i.e., in the direction of arrow F. Valve  64  may take any of many forms, but it has been found that a nylon poppet check valve, with no spring, works quite well. 
     Vent tube assembly  58  includes leg-like extension  66  that extends away from tube  59  and upwardly to a point above the normal oil level of rear axle housing  28 , shown as L in FIG.  5 . Tubes  59  and  66  are hollow to allow fluid flow therethrough, and the end of tube  59  having flange  61  is aligned with balance hole  54  through faceplate  50 . Shafts  29  and  38  are space away from vent tube assembly  58  as can be seen in FIG.  4 . 
     As a matter of clarification, it should be understood that the output gears  36  and  37  rotate at generally high speeds during vehicle transport/roading, in the range of 5,000 rpm. When these gears are rotated in one direction, as they would be when tractor  10  is moving rearward (i.e., to the right in FIGS.  1  and  2 ), they create a suction, drawing oil into the splitter gearbox from the rear axle that is the hydraulic sump of the vehicle. Too much oil in the splitter gearbox creates churning and constant power losses (parasitic losses). When gears  36  and  37  rotate in the opposite direction, i.e., the tractor is moving forward (i.e., to the left in FIGS.  1  and  2 ), they create a pumping action and oil is pumped out of the splitter gearbox. Thus, parasitic losses, similar to those described above, are created. 
     Balance hole  54  is present between the splitter gearbox  30  and the rear axle housing  28  to allow oil to drain from gearbox  30 , which is pressure lubed, to the rear axle housing  28 . Hole  54  is located at a level where the output gears  36  and  37  mesh. When the tractor  10  is driven forward, the output gears rotate in such a manner as to pump oil from the gearbox  30  into the rear axle through the balance hole. As oil is drawn into the gearbox  30 , the level increases, covering the gears and creating high parasitic losses due to churning. The vent tube assembly is mounted such that one end of tube  59  covers the balance hole  54 , one end connects to a check valve  64  at the same level as the balance hole, with the free flow direction from the gearbox to the rear axle housing  28 , and leg  66  extends above the oil level L of the rear axle. 
     When the tractor is driven in reverse, the vent tube assembly breaks the vacuum at the balance hole created by the output gears of the splitter gearbox, thereby not allowing oil to be drawn into the splitter gearbox and keeping the parasitic churning losses low. When the tractor is driven in this direction up an incline, the check valve  64  closes off due to the oil level rising in the splitter gearbox  30 /rear axle housing  28  junction and the vent tube then breaks the vacuum created by the output gears of the splitter gearbox as above. 
     When the tractor is driven forward, the check valve allows the oil that is being pumped by the splitter gearbox output gears through the balance hole  54 , to be drained into the rear axle, keeping the parasitic churning losses low. An additional balance hole may be added as needed to help with the balancing issue. 
     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 inventions. Accordingly, the following claims are intended to protect the invention broadly as well as in the specific form shown.