Abstract:
A transmission ( 12 ) for a vehicle ( 10 ) includes a gear arrangement having a gear shaft ( 44 ) and a gear ( 48,66 ) mounted to the gear shaft ( 44 ). The gear ( 48,66 ) is axially movable and rotationally fixed relative to the gear shaft ( 44 ). A housing ( 28 ) includes an access opening ( 56 ) and an access cover ( 54 ) over the access opening ( 56 ). The access cover ( 54 ) rotatably carries one end of the gear shaft ( 44 ). The access opening ( 56 ) is sized and shaped to allow the gear ( 48,66 ) to be moved through and out of the housing ( 28 ).

Description:
FIELD OF THE INVENTION 
     The present invention relates to work machines, and, more particularly, to transmissions used in such work machines. 
     BACKGROUND OF THE INVENTION 
     A work machine such as an agricultural tractor may be driven with motive force taking several different forms, such as a rear wheel drive, four wheel drive (4WD), mechanical front wheel drive (MFWD), track-type drive, etc. In the case of an MFWD equipped tractor, the front wheel drive typically is not full time, and an electronic switch in the operator&#39;s station is used to switch between rear wheel drive and MFWD mode. 
     An MFWD tractor may include an internal combustion (IC) engine which provides input power to a transmission, which in turn is coupled with and drives the rear axles through a rear end differential. The transmission may also include an output shaft, typically facing in the forward direction, which connects via a drive shaft or the like with the MFWD at the front end of the tractor. 
     An operator may order a new MFWD equipped tractor with a selected tire combination between the front and rear tires, or may desire to change to a different tire combination for some reason. Depending on the selected tire combination, the transmission may need to have a different gear ratio for the output shaft to the MFWD. Conventional transmissions with an output shaft for an MFWD typically do no allow the gear ratio to be easily changed, either during initial assembly or in a retrofit situation. It is thus necessary to use a different transmission with a different gear ratio, or disassemble the transmission and replace the gear set coupled with the MFWD output shaft. Either solution is not optimal for efficiency and cost. 
     What is needed in the art is a tractor with a transmission which may be modified to provide a different gear ratio to the MFWD output shaft, without having to completely disassemble or replace the transmission. 
     SUMMARY OF THE INVENTION 
     The invention in one form is directed to a transmission for a vehicle, including a gear arrangement having a gear shaft and a gear mounted to the gear shaft. The gear is axially movable and rotationally fixed relative to the gear shaft. A housing includes an access opening and an access cover over the access opening. The access cover rotatably carries one end of the gear shaft. The access opening is sized and shaped to allow the gear to be moved through and out of the housing. 
     The invention in another form is directed to a transmission kit for a vehicle, including a power output having an output shaft and an output gear carried by the output shaft. An idler arrangement has an idler shaft and a plurality of drive gears. Each drive gear is selectively mountable to the idler shaft so as to be axially movable and rotationally fixed relative to the idler shaft. Each drive gear has a different number of teeth relative to another drive gear, and each drive gear is configured for driving the output gear. A housing includes an access opening and an access cover over the opening. The access cover rotatably carries one end of the idler shaft, and the access opening is sized and shaped to allow the drive gear to be moved through and out of the housing. 
     The invention in yet another form is directed to a work machine, including an engine and a transmission coupled with the engine. The transmission includes a power input with an input shaft and an input gear carried by the input shaft, and a power output with an output shaft and an output gear carried by the output shaft. An idler arrangement mechanically interconnects the input gear and the output gear. The idler arrangement includes an idler shaft and a drive gear. The drive gear is mounted to the idler shaft so as to be axially movable and rotationally fixed relative to the idler shaft. A housing includes an access opening and an access cover over the opening. The access cover rotatably carries one end of the idler shaft, and the access opening is sized and shaped to allow the drive gear to be moved through and out of the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of a transmission of the present invention used in an agricultural tractor; 
         FIG. 2  is side, sectional view through the transmission shown in  FIG. 1 , taken along line  2 - 2 ; 
         FIG. 3  is an enlarged view of detail A shown in  FIG. 2 ; and 
         FIG. 4  is an exploded perspective view of the idler arrangement shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to  FIGS. 1 and 2 , there is shown a portion of a work machine  10  in the form of an agricultural tractor, particularly the rear end drive train of the tractor. Although shown as an agricultural tractor, it is possible that work machine  10  could be in the form of a different type of work machine, such as a construction tractor or forestry machine. 
     Tractor  10  includes a transmission  12  which is coupled with a rear end differential  14 , which in turn drives a pair of rear axels  16 . Each rear axel  16  includes an outboard hub  18  to which a respective rear drive wheel (not shown) s mounted. 
     Transmission  12  includes a driven shaft  20  which is mechanically coupled with and receives rotational input power from IC engine  22 , shown schematically in  FIG. 1 . Driven shaft  20  transfers rotational power via appropriate gearing to differential drive shaft  24 , which in turn extends from the rear of and provides rotational input power to differential rear end gear set  26  (see  FIG. 2 ). 
     Driven shaft  20  extends through and is rotatably carried by housing  28 , which likewise houses and rotatably carries a number of other components. Also positioned within and carried by housing  28  is an idler arrangement  30  which mechanically interconnects between a power input  32  and a power output  34 . Referring to  FIGS. 2 and 3 , power input  32  includes an input shaft  36  and an input gear  38  carried by input shaft  36 . In the embodiment shown, input shaft  36  is in fact the differential drive shaft  24 , but could be a different rotatable drive shaft providing input power to idler arrangement  30 . Input shaft  36  receives input power from driven shaft  20  coupled with IC engine  22 . 
     The terms power input  32  and power output  34  are used relative to idler arrangement  30 . That is, power input  32  provides input power to idler arrangement  30 , and power output  34  receives and provides power output from idler arrangement  30 . 
     Power output  34  similarly includes an output shaft  40  and an output gear  42  carried by output shaft  40 . In the embodiment shown, output shaft  40  extends through housing  28  and provides rotational output power to the MFWD at the front axle of tractor  10 . Output gear  42  is clutched to output shaft  40  so that output gear  42  positively rotates with output shaft  40  when the MFWD is engaged by actuation of a switch (not shown) in the operator&#39;s station. 
     Idler arrangement  30  ( FIGS. 3 and 4 ) includes an idler shaft  44 , driven gear  46  and drive gear  48 . Driven gear  46  is rigidly fixed to idler shaft  44  and rotates therewith during operation. Drive gear  48  has an inside diameter which is splined to the outside diameter of idler shaft  44  when in an installed position. Drive gear  48  abuts against a shoulder  50  on idler shaft  44  for retention in one axial direction, and is retained by a snap ring  52  in the other axial direction (with a thrust washer  53  between snap ring  52  and drive gear  48 ). 
     An access cover  54  forms part of housing  28 , and fits within an access opening  56  formed in housing  28 . Access cover  54  carries a pair of annular seals  58  which seal with the inside diameter of access opening  56 . Access cover  54  is fastened to housing  28  using three bolts  60 , or other suitable fastening technique. 
     Access cover  54  also defines a bearing support which supports a bearing  62 , which in turn has an inner race which rotatably carries an outboard end of idler shaft  44 . The outboard end of idler shaft  44  has a chamfer  64  which provides easier piloting of idler shaft  44  into the inner race of bearing  62 . 
     Under certain conditions of operation of tractor  10 , such as a particular tire combination, etc., it may be desirable and/or necessary to change the input/output (I/O) ratio of idler arrangement  30 , thereby changing the rotational drive speed of output shaft  40  to the MFWD. In the embodiment shown, t is possible to select between a plurality of drive gears on idler arrangement  30 , including drive gear  48  and an additional drive gear  66  ( FIG. 3 ). Each of drive gears  48  and  66  have a same inside diameter and same spline configuration allowing coupling with the exterior splines on idler shaft  44 . Drive gears  48  and  66  differ from each other in that they have a different number of teeth and a slightly different overall outside diameter. In the embodiment shown, drive gear  48  has thirty teeth and drive gear  66  has thirty-one teeth, with an overall outside diameter change of less than one millimeter. 
     To exchange drive gear  66  for drive gear  48 , or vice versa, fasteners  60  are removed from access cover  54 , and access cover  54  is slid in an axial direction out of access opening  56 . Bearing  62  is pressed within access cover  54  and is removed with access cover  54  from idler shaft  44 . Snap ring  52  and thrust washer  53  are then removed from idler shaft  44  and withdrawn through access opening  56 . Drive gear  48  is slid in an axial direction so that the interior splines disengage from the exterior splines on idler shaft  44 . The overall outside diameter of drive gear  48  is slightly less than the inside diameter of access opening  56  so that drive gear  48  may be withdrawn through access opening  56 . Drive gear  66  is then moved through access opening  56  and slid in an axial direction onto idler shaft  44  until seated against shoulder  50 . Snap ring  52  and thrust washer  53  are re-installed on idler shaft  44 , and access cover  54  is installed into access opening  56  and bolted to housing  28 . During the insertion of access cover  54  into access opening  56 , chamfer  64  self-centers idler shaft  44  within the inner race of bearing  62 . 
     Using the present invention as described above, the I/O ratio of idler arrangement  30  to output shaft  40  may be changed. With conventional transmissions, it would be necessary to remove transmission  12  from rear end differential  14  and use a different transmission or disassemble/reassemble the various components and gears from the back side of transmission  12  to change the I/O ratio of output shaft  40 . With the present invention, the I/O ratio may be quickly and easily changed without having to disassemble transmission  12  from rear end differential  14 , or disassemble other components within transmission  12 . The present invention therefore provides a fast and easy way to change the I/O ratio of output shaft  40  to the MFWD on the front axel. 
     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.