Abstract:
A compact creeper gear arrangement ( 70 ) for a multiple speed transmission ( 12 ) in which the creeper gear input ( 78 ) and output shafts ( 88 ) are laterally spaced from and parallel to the major shafts within the transmission. The creeper gear arrangement ( 70 ) utilizes an input gear ( 74 ) integral with one of the speed range gears ( 72 ) and selectively coupled to a shaft ( 24 ) that provides an input to a mechanical front wheel drive assembly ( 41 ). The creeper gear arrangement ( 70 ) is a dual speed selectively engageable transmission where much of the mechanism is located within otherwise unused space within the transmission.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to work machines and more particularly to transmissions used in such work machines. 
       BACKGROUND OF THE INVENTION 
       [0002]    A work machine such as an agricultural tractor may be driven with motive force taking several forms such as a rear wheel drive, four wheel drive (4WD), mechanical front wheel drive (MFWD), endless track drive and others. In the case of an MFWD equipped tractor, the front wheel drive is typically not full time and an electronic switch in the operator station is used to switch between rear wheel drive and MFWD mode. 
         [0003]    A work machine incorporating such a transmission is powered by a prime mover, usually consisting of a compression ignition or diesel engine. Such engine operates over a range of engine rpm&#39;s but has certain operating conditions in which the torque output and fuel efficiency are at a high level. The purpose of the transmission in such a work machine is to match ground speed to the optimal engine operating conditions so as to provide fuel efficient and effective operation. 
         [0004]    Such work machines have a condition where the vehicle is required to move forward along the ground at a velocity substantially lower than the normal operational velocity of the vehicle. To accomplish this purpose, creeper gear arrangements may be provided in transmissions for work vehicles. These creeper gear arrangements may be a single speed or multiple speed arrangement. In prior art transmissions the creeper gear has been incorporated before or after the speed ratio gears or may function as a separate range. Typically, these designs add between approximately 50 millimeters and 75 millimeters of overall length to the transmission. With such a significant increase in length, the vehicle envelope is affected in a way that works against a compact work vehicle arrangement. 
         [0005]    What is needed therefore in the art is a compact creeper gear arrangement for a transmission in a work vehicle. 
       SUMMARY OF THE INVENTION 
       [0006]    In one form, the invention includes a creeper gear arrangement for a vehicle transmission having a driven range gear and a main output drive shaft co-axial with the range gear, the range gear being selectively coupled and decoupled to the main output drive shaft. The creeper gear arrangement includes a creeper input gear affixed to and co-axial with the range gear and a creeper driven gear meshing with the creeper input gear and affixed to a creeper gear input shaft parallel to and spaced from the main output drive shaft. A pair of intermeshing gears is respectively affixed to the main output drive shaft and a secondary output shaft co-axial with the creeper gear input shaft. A device selectively interconnects the creeper gear input shaft with the secondary output shaft when the range gear is decoupled with the main output drive shaft. 
         [0007]    In another form, the invention is a vehicle transmission including: a main input drive shaft; a main output drive shaft; a range gear positioned over and co-axial with the main output drive shaft, the range gear being driven from the main input drive shaft and selectively coupled and decoupled to the main output drive shaft. A creeper input gear is affixed to and co-axial with the range gear. A creeper driven gear meshes with the creeper input gear and is affixed to a creeper gear input shaft parallel to and spaced from said main output drive shaft. A pair of intermeshing gears is respectively affixed to the main output drive shaft and a secondary output shaft co-axial with the creeper gear input shaft. A device selectively interconnects the idler shaft with the secondary output shaft when the range gear is decoupled with the main output drive shaft. 
         [0008]    In yet another form, the invention is a work machine having an engine, a mechanical front wheel drive, and a vehicle transmission including a main input drive shaft, a main output drive shaft and a range gear positioned over and co-axial with the main output drive shaft, the range gear being driven from the main input drive shaft and selectively coupled and decoupled to the main output drive shaft. A creeper input gear is affixed to and co-axial with the range gear. A creeper driven gear meshes with the creeper input gear and is affixed to a creeper gear input shaft parallel to and spaced from the main output drive shaft. The creeper driven gear is affixed to and co-axial with the creeper gear input shaft. A pair of intermeshing gears are respectively affixed to the main output drive shaft and a secondary output shaft co-axial with the idler shaft A device selectively interconnects the creeper gear input shaft with the secondary output shaft when the range gear is decoupled with the main output drive shaft. The secondary output shaft provides a drive input to the mechanical front wheel drive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  shows a perspective view of a work machine and transmission incorporating a creeper gear according to the present invention. 
           [0010]      FIG. 2  is a side, sectional view through the transmission shown in  FIG. 1 , taken along line  2 - 2 ; 
           [0011]      FIG. 3  is an enlarged view of detail A shown in  FIG. 2 ; 
           [0012]      FIG. 4  is an enlarged detailed view of a portion of  FIG. 1  taken on lines  4 - 4  of  FIG. 1 ; and 
           [0013]      FIG. 5  is a perspective view of a bearing assembly used in the arrangements shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    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. 
         [0015]    Tractor  10  includes a transmission  12  which is coupled with a rear end differential  14 , which in turn drives a pair of rear axles  16 . Each rear axle  16  includes an outboard hub  18  to which a respective rear drive wheel (not shown) is mounted. 
         [0016]    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 rear end differential gear set  26  (see  FIG. 2 ). 
         [0017]    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 . 
         [0018]    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 . 
         [0019]    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  (see  FIG. 3 .) 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 ). 
         [0020]    An access cover  54  forms part of housing  28 , and fits within an access opening  56  formed in housing  28 . 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 . Access cover  54  is fastened to housing  28  using three bolts  60 , or other suitable fastening technique. 
         [0021]    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, shown schematically in  FIG. 1  by reference character  41  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. 
         [0022]    More particularly, a clutch arrangement  62  generally includes output gear  42 , shift collar  64 , annular piston  66  and spring  68  ( FIG. 3 ). Output gear  42  is selectively coupled to output shaft by the clutch arrangement  62  to provide a power output to the MFWD. 
         [0023]    As stated above, the transmission  12  for the work machine  10  has normal speed range gears, a portion of which are shown on input shaft  24  in  FIGS. 2 and 3 . The gears are placed on shaft  24  and intermesh with gears on the input shaft  22  in such a fashion that multiple speed ranges from the work machine  10  may be achieved while maintaining, the engine  22  at an optimum duty cycle condition. For such a transmission it may also have a creeper gear arrangement, illustrated by reference character  70  in  FIGS. 2 ,  3  and  4 . Creeper gear arrangement  70  has, an input from a speed range gear  72  telescoped over shaft  24 . Speed range gear  72  may be one of the speed range gears but, as herein shown, is the A range gear which is rotating whenever the transmission is engaged. Gear  72  is coupled or decoupled to shaft  24  by a clutch arrangement  73  shown in  FIGS. 2 and 3 . 
         [0024]    As shown particularly in  FIG. 4 , speed range gear  72  has integral therewith a creeper input gear  74  coaxial with and affixed to speed range gear  72 . Creeper input gear  74  meshes with a corresponding gear  76  affixed to gear  76  is affixed to and rotates with a tubular creeper gear input shaft  78  parallel to and spaced from the axis of shaft  24 . As shown herein, creeper gear input shaft  78  is journaled on one end by a bearing assembly  80  mounted in housing  28  and at the other end by a bearing assembly  82 , also mounted in housing  28 . Creeper gear input shaft  78  extends to an end  84  having an outwardly splined section  86 . A creeper gear output shaft  88  is coaxial with and telescoped into tubular idler shaft creeper gear input shaft  78  and is supported at the left end as shown in  FIG. 4  by shaft  44  which is journaled in housing  28  by means of a bearing assembly  90 . The left end of creeper gear output shaft  88  is suitably splined to shaft  44  at  92  so that the shafts are coaxial with, and rotate together. 
         [0025]    The right end of shaft  88  has an outwardly facing splined section  94  terminating in a shoulder  96  for a bearing assembly  98  that is mounted in frame  100  suitably affixed to housing  28 . An axially displaceable sleeve  102  is received over the splines  94  and has inwardly directed splines  104  so that sleeve  102  rotates with shaft  88  but is axially displaceable along shaft  88 . Sleeve  102  has a groove  106  receiving a fork  108  for an appropriate mechanism to move sleeve  102  between a plurality of positions. In the position illustrated in  FIG. 4 , the sleeve  102  is in a neutral position where the outwardly facing spline  86  of creeper gear&#39;input shaft  78  does not engage the inwardly facing splines  104  of sleeve  102  and, as such, the creeper gear is not operable. If fork  108  is manipulated to move sleeve  102  to the left as shown in  FIG. 4 , splines  86  inter-engage with splines  104  to provide a direct connection between creeper gear input shaft  78  and creeper gear output shaft  88 . 
         [0026]    The creeper gear arrangement  70  may be a single speed in which sleeve  102  engages or disengages the connection between creeper gear input shaft  78  and output shaft  88 . However, as illustrated herein, creeper gear arrangement  70  has a second speed in which a different speed ratio is utilized. For this purpose, a gear  110  is telescoped over and journaled with respect to creeper gear input shaft  78 . Gear  110  has an annular extension  112  terminating in inwardly facing splines  114  sized to inter-engage with outwardly facing splines  108  on sleeve  102 . Gear  110  meshes with a gear set  116  journaled by means of bearing assemblies  118  and  120 . Gear set  116  has a first gear  122  meshing with gear  110  and a second gear  124  meshing with a gear  126  integral with creeper gear input shaft  78 . 
         [0027]    Accordingly, movement of the sleeve  102  to the right from the position shown in  FIG. 4  engages splines  108  and  114  to provide a connection between gear  110  and output shaft  88  to provide a low speed creeper gear. Gear  110  meshes with the gear set  116  having gear  124  meshing with gear  126  on the creeper gear input shaft  78 . In this position, the power flow is from the creeper gear input shaft  78  through gear  126  meshing with gear  124 . Gear  122  meshes with gear  110  which connects to creeper gear output shaft  88  through splines  108  and  114 . This provides a second speed for the creeper gear output. 
         [0028]    The creeper gear output shaft is connected to shaft  44  which in turn is connected to shaft  24  through the gear set  38  and  46 . As indicated previously, the output of shaft  24  is to the differential arrangement for transmission  12  but, in addition, is an input to the gear set providing power to the MFWD assembly  41 . 
         [0029]    For the neutral position illustrated in  FIG. 4 , rotation of the A range gear  72  and integral creeper input gear  74  cause the creeper gear input shaft  78  to rotate. However, because the sleeve  102  is neither engaged directly with between creeper input shaft  78  and creeper gear output shaft  88  and does not engage the splines  108  and  114  to the gear  110 , no movement is translated to the creeper gear output shaft  88 . The connection between shaft  44  and the MFWD is controlled in the normal fashion to either engage or disengage the MFWD drive at the front of the vehicle. 
         [0030]    Activation of the creeper gear arrangement  70  is first initiated by moving the clutch assembly  73  so that gear  72  is de-coupled from shaft  24 . The sleeve  102  is then moved axially to the left from the position shown in  FIG. 4  to a high speed creeper gear ratio so that sleeve  102  directly couples the creeper gear input shaft  78  and the creeper gear output shaft  88 . This rotation is transferred to the differential drive shaft  24  through the gear set  38  and  46  to provide a creeper gear arrangement. It should be noted that in this position the A range gear  72 , and thus the creeper input gear  74 , are turning relative to differential drive shaft  24 . In order to more appropriately accommodate the radial loads on these gears, a sleeve bearing  128  is telescoped over differential input shaft  24  as shown in  FIG. 5 . Thus, the power flow is from a gear engaging A range gear  72  through the creeper input gear  76 , creeper gear input shaft  78  and directly to the creeper gear output shaft  88  to the shaft  44 , which, in turn, drives the differential input shaft  24  through the intermeshing of gears  46  and  38 . The clutch mechanism  62  is selectively used to engage or disengage the MFWD  41 , either when the transmission  12  is in the creeper mode or not. 
         [0031]    If the second speed for the creeper gear arrangement  70  is desired to be utilized, the sleeve  102  is displaced to the right from the position shown in  FIG. 4  so that the splines  108  and  114  are engaged. In this position, the power flow is from the A range gear  72  through the creeper input gear  74  through gear  76  to creeper gear input shaft  78 . From there it is transferred through meshing gears  126  and  124  and through gear  122  to gear  110  which is then coupled to the creeper gear output shaft  88 . Thus it is seen that a second creeper gear input speed is available. 
         [0032]    The benefits of such an arrangement are that the creeper gear input and output shafts are spaced from but parallel to the main power shafts in the transmission. This enables any additional space to be lateral rather than axial to provide an extremely compact transmission. Since the transmission incorporates an MFWD, the input shafts for such a drive are utilized to accommodate the input and output creeper gear shafts. In addition, the sleeve  102  and associated interconnections are placed in the otherwise empty space in the transmission  12  underneath the differential assembly  26 . This is shown particularly in  FIG. 2 . This arrangement enables a highly compact transmission with minimum axial length but with the full features shown in substantially larger transmissions. 
         [0033]    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.