Abstract:
A track suspension is disclosed including a track, a drive wheel engaged with the track, a wheel support, a drive wheel shaft rotationally engaged with the wheel and a drive wheel shaft support. The wheel support is adjustably securable to the drive wheel shaft support in a plurality of laterally disposed positions and the wheel is slidingly positionable with respect to the length of the drive wheel shaft in correspondence with the adjusted position of the wheel support. Also disclosed is a tracked vehicle including a frame, at least one track suspension including a track, a drive wheel engaged with the track, a wheel support, a drive wheel shaft and a drive wheel shaft support. The wheel support is adjustably securable to the drive wheel shaft support in a plurality of laterally disposed positions and the wheel is slidingly positionable with respect to the length of the drive wheel shaft in correspondence with the adjusted position of the wheel support. Also disclosed is a method of adjusting the track width of a tracked vehicle, including the steps of (a) unfixing a wheel support of a track suspension from a drive wheel shaft support, (b) adjusting the lateral location of the track suspension with respect to the drive wheel shaft support, and (c) affixing the wheel support to the drive wheel shaft support.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a tracked vehicle. It relates particularly to a tracked work vehicle having a plurality of endless track drives, at least a portion of them both driveable and steerable. 
     BACKGROUND OF THE INVENTION 
     It has long been known to provide work vehicles with endless track assemblies, or tracks (sometimes referred to as “crawler treads”), for ground support in order to provide increased traction and support, or flotation, upon moist or loosely packed soils. Due in part to their larger footprints which compact agricultural field soils less than do the tires of wheels of typical agricultural tractors, tracked vehicles have in recent years become increasingly popular in crop farming as well, particularly in connection with larger, heavier and more powerful tractors. Track assemblies, including undercarriage such as idler and bogie wheels, pivot brackets and other supporting structure may be referred to as track suspensions. 
     Maneuverability of a tractor with a connected implement is of importance, especially at the headlands of a field (i.e., at the ends of crop rows) where a tractor with implement must be turned 180 degrees. Larger wheeled tractors, which are provided with rigid frames having larger turning radii if provided with conventional front wheel steering systems, can require excessive maneuvering and/or width of headland. Their frames are therefore often hinged, or articulated, and they are steered by changing the angle of a front frame with respect to a rear frame, typically by use of a hydraulic cylinder bracketing a pivot joining the front and rear frames. This is an expensive configuration of construction, however, and is generally used only on very large tractors. 
     Larger tracked tractors utilizing articulated frames are produced in the QUADTRAC™ series of models by Case Corporation, assignee of the present invention. These utilize four endless track assemblies, one each generally located near the front and rear ends of the right and left sides of the tractor. Other tracked tractors generally utilize rigid frames with one endless track on the left side and another on the right side, and are steered by changing speed of either endless track with respect to the other. Such tractors can turn in extremely tight circles, but, in the hands of an inexperienced or inattentive operator, can easily and quickly be inadvertently jackknifed with an implement and damage the implement. Moreover, they provide a harsh ride and generally lack the directional stability desired for ease in making or following long, straight and parallel crop rows. 
     Because various types of crops often require differing row spacings for efficient utilization of a field, tractors are preferably provided with adjustable track width; i.e., the widths in front and rear elevation views between centerlines of tires or endless track assemblies. While this is relatively easily accomplished with wheeled tractors, it is generally a time-consuming and costly operation with a tracked tractor, requiring significant undercarriage disassembly. 
     It would be advantageous to provide for a work vehicle, such as an agricultural tractor, to offer the better ride and directional stability of a wheeled tractor while also offering the better traction and lesser soil compaction of a tracked tractor, without incurring the expense of an articulated configuration. 
     It would also be advantageous to provide for such a work vehicle to include endless track drives which are compact and which are relatively easily repositioned to change vehicle track width. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention relates to a track suspension for a tracked vehicle, the vehicle having a longitudinal axis, the suspension including a track, a rotatable drive wheel engaged with the endless track and configured for driving the endless track, a nonrotatable wheel support configured for supporting the drive wheel in rotation; a rotatable drive wheel shaft having a length, rotationally engaged with the drive wheel, and configured for driving the drive wheel in rotation; and a nonrotatable drive wheel shaft support configured for supporting the drive wheel shaft in rotation and configured to be steerable with respect to the vehicle, wherein the wheel support is adjustably securable to the drive wheel shaft support in a plurality of laterally disposed positions and the drive wheel is slidingly positionable with respect to the length of the drive wheel shaft in correspondence with the adjusted position of the wheel support, the laterally disposed position of the endless track suspension thereby being adjustable with respect to the longitudinal axis. 
     In accordance with another embodiment, the present invention relates to a dual endless track suspension for a tracked vehicle having a left side and a right side, the suspension including a first endless track suspension extending from the left side, and a second endless track suspension, positioned in spaced-apart and opposing relationship to the first endless track suspension, and extending from the right side, the first and second endless track suspensions each including a track, a rotatable drive wheel engaged with the endless track and configured for driving the endless track assembly, a nonrotatable wheel support configured for supporting the drive wheel in rotation; a rotatable drive wheel shaft having a length, rotationally engaged with the drive wheel, and configured for driving the drive wheel in rotation; a nonrotatable drive wheel shaft support configured for supporting the drive wheel shaft in rotation; at least one endless track support undercarriage coupled to the wheel support; a final drive including a planetary gear set having a sun gear slidingly positionable with respect to the length of the drive wheel shaft while remaining rotationally engaged with the drive wheel shaft, an internal ring gear secured to the drive wheel and positioned coaxial and coplanar with the sun gear, and at least one planet gear positioned intermediate the sun gear and the ring gear, the planet gear rotatably supported by the wheel support; and a flexible coupling for flexibly coupling the drive wheel shaft to a power source, the major axis of the drive wheel shaft and the drive wheel shaft support being adjustably pivotable about a substantially vertical axis for steering the vehicle. 
     In accordance with another embodiment, the present invention relates to a tracked vehicle including a frame having a longitudinal axis, at least one endless track suspension, the endless track suspension including a track, a rotatable drive wheel engaged with the endless track and configured for driving the endless track assembly, a nonrotatable wheel support configured for supporting the drive wheel; a rotatable drive wheel shaft having a length, rotationally engaged with the drive wheel, and configured for driving the drive wheel in rotation; and a nonrotatable drive wheel shaft support configured for supporting the drive wheel shaft in rotation and steerably coupled to the frame, wherein the wheel support is adjustably securable to the drive wheel shaft support in a plurality of laterally disposed positions and the drive wheel is slidingly positionable with respect to the length of the drive wheel shaft in correspondence with the adjusted position of the wheel support, the laterally disposed position of the endless track suspension with respect to the longitudinal axis being thereby adjustable. 
     In accordance with another embodiment, the present invention relates to a method of adjusting the track width of a tracked vehicle, the method including the steps of (a) unfixing a wheel support of a track suspension from a drive wheel shaft support of the vehicle, (b) adjusting the lateral location of the endless track suspension from a first position to a second position with respect to the drive wheel shaft support, and (c) affixing the wheel support of the endless track suspension to the drive wheel shaft support. 
    
    
     Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an agricultural tractor having an adjustable track width, steerable, front endless track drive; 
     FIG. 2 is a schematic plan view of the tractor, showing track drives in various track width and steering positions; 
     FIG. 3 is an exploded fragmentary view of the adjustable track width, steerable track drive; 
     FIG. 4 is a fragmentary front elevation of the track drive taken at line  4 — 4  of FIG. 1; 
     FIG. 5 is a fragmentary sectional elevation showing a planetary gear set of the track drive, taken at line  5 — 5  of FIG. 4; 
     FIG. 6 is a fragmentary, sectional plan view of the track drive in a first position of track width adjustment, taken at line  6 — 6  of FIG. 4; 
     FIG. 7 is a fragmentary, sectional elevation of the track drive in the first position of track width adjustment, taken at line  7 — 7  of FIG. 6; 
     FIG. 8 is a fragmentary plan view of the track drive in a second position of track width adjustment; 
     FIG. 9 is a fragmentary front sectional elevation of the track drive in the second position of track width adjustment, taken at line  9 — 9  of FIG. 8; and 
     FIG. 10 is a fragmentary plan view of the track drive steered in a first position in solid lines and in a second position in phantom lines. 
     Before explaining at least one embodiment of the invention in detail it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 which shows an agricultural tractor  102  provided with track suspensions; i.e., endless track assemblies including tracks  126 , wheels (shown as idler wheels  128  and bogie wheels  130 ), and a pivot frame  132 . Tractor  102  includes a front  104  and a rear  106 , a left side  110  and a right side  108  and a longitudinal axis  103 . Tractor  102  further includes two (one is shown, at rear  106 ) rigid (i.e., nonsteerable) endless track drives or rigid track drives  124 ; and two (shown at front  104 ) steerable, adjustable-track width (indicated by dimension “W”) endless track drives or steerable track drives  122 . In an alternative embodiment (not shown), a tractor includes steerable, adjustable-track width track drives at both front  104  and rear  106 . 
     It is to be understood that, in the phrase “adjustable track width,” the phrase “track width” refers to a width, transverse with respect to axis  103 , between centerlines of ground support devices (e.g., wheels, endless track assemblies) in a front or rear elevation view of a vehicle, as indicated by dimension “W” in FIG.  1 . In the phrases “track assembly” or “track drive,” however, the word “track” refers to an endless track comprising plates, bushings and pins and utilized as a ground support device. The word “endless” refers to the fact that the track, when in use, forms an endless loop and does not mean that loop cannot be disassembled to form one or more individual sections or strips of track. The word “steering” refers to operator-controlled changing of disposition in azimuth of one or more steerable track drives  122  with respect to frame  112  while tractor  102  is under way and for the purpose of guiding tractor  102  in a course or direction of movement selected by the operator. 
     A typical drive train  134  is also shown, and includes a power source (shown as an engine  114 ), a transfer unit  116  coupled to engine  114 , a front differential unit (shown as a vehicular differential gear unit  118  coupled to transfer unit  116  and to at least one steerable track drive  122 , and a rear differential unit  120  coupled to transfer unit  116  and to at least one rigid track drive  124 . In alternative embodiments (not shown), other types of drive train (e.g., hydrostatic, electromotive) are provided in place of that shown. 
     Steerable track drive  122  includes an endless track  126 , a drive wheel  136  coupled to endless track  126 , idler wheels  128 , and one or more bogie wheels  130 . Bogie wheels  130  are supported by, and ride upon, a portion of endless track  126  which is contact with a surface upon which tractor  102  is placed. Drive wheel  136  is supported by a wheel support  200  (shown in FIGS.  3  and  4 ), which is itself supported by a track support undercarriage (shown as a bogie wheel pivot frame  132  in FIGS. 4,  7  and  9 ) including a pivot  210  having a pivot pin  212 . Bogie wheel pivot frame  132  also supports bogie wheels  130  and idler wheels  128 . Steerable track drive  122  is movably coupled to frame  112  by a steering actuator  138 . 
     FIG. 2 is a fragmentary, schematic plan view of tractor  102  showing frame  112 , transfer unit  116 , front differential unit  118 , rear differential unit  120 , rigid track drives  124  and steerable track drives  122 . Rigid track drives  124  are shown in retracted positions  142   a  with respect to axis  103 , and steerable track drives  122  are shown in retracted positions  140 a (both denoted by indicia “R” and solid lines) for a lesser track width “W.” Rigid track drives  124  are also shown in extended positions  142   b  with respect to axis  103 , and steerable track drives  122  are also shown in extended positions  140   b  (both denoted by indicia “E” and double-dashed phantom lines) for a greater track width “W.” Steerable track drives  122  are additionally shown in steered, retracted positions  140 c (denoted by indicia “R” and single-dash phantom lines) and in steered, extended positions  140   d  (denoted by indicia “E” and triple-dash phantom lines), wherein they are pivoted with respect to axis  103  about steering axes  144 . 
     FIG. 3 is an exploded, fragmentary, perspective view of tractor  102  showing members of frame  112  and of steerable track drive  122  primarily related to power transmission, steering and track width “W” adjustment of steerable track drive  122 . Frame  112  includes a shaft support, shown as a hollow axle shaft housing  162 , which houses and supports an axle shaft  160  (shown in FIG. 7) for coupling steerable track drive  122  to front differential unit  118 . An axle shaft  160  extends through axle shaft housing  162  from a first end (not shown) at front differential unit  118  to a second end  161  (shown in FIG. 7) in the region of steering axis  144  (described below). 
     Axle shaft housing  162  has an outer end  163  adjacent steerable track drive  122 . A first steering knuckle  164  is affixed to outer end  163 . A second steering knuckle  166  is pivotally affixed to first steering knuckle  164  by kingpins  168  engaging apertures  165  in first steering knuckle  164  and apertures  172  in second steering knuckle  166 , thereby providing a steering pivot joint and defining steering axis  144 . Second steering knuckle  166  is thus pivotally free to be steered with respect to first steering knuckle  164  of frame  112 . The angle of steering is controlled by hydraulic power steering actuator  138  having a cylinder portion  139 , a rod  184 , a first end (not shown) affixed to a stationary member (e.g., axle shaft housing  162  of frame  112 ) and a second end  180  including a fitting, shown as a tie rod end  182 , for pivotal connection to a cylindrical or spherical member shown as a pin  188 . Pin  188  is affixed to a bellcrank  186 , which is rigidly coupled to second steering knuckle  166 . The components of the steering joint are preferably disposed and dimensioned to provide a steering angle about steering axis  144  of at least plus and minus 15 degrees, preferably plus and minus 55 degrees. 
     Steerable track drive  122  includes a drive wheel support  200  (shown also in FIGS.  4  and  6 - 10 ), a drive wheel  136 , a drive wheel shaft  190  and a final drive  146 . Wheel support  200  is adjustably secured to second steering knuckle  166 , and is configured to be slidably movable with respect to second steering knuckle  166  for adjustment of lateral position of steerable track drive  122  with respect to frame  112 , and thereby of tractor  102  track width “W.” Position of wheel support  200  with respect to second steering knuckle  166  is maintained and secured after adjustment by removably affixing wheel support  200  to second steering knuckle  166 ; e.g., by threaded fasteners  174  projecting through selected clearance holes, or cylindrical apertures,  176  in wheel support  200  and engaging threaded apertures  178  in second steering knuckle  166 . This provides discrete increments of track width “W” adjustment, each increment being equal to a pitch  177  between adjacent apertures  176  in wheel support  200 . In an alternative embodiment (not shown), infinitesimal adjustments of track width “W” are provided; for example, by replacing the pitched cylindrical apertures  176  in wheel support  200  by slotted apertures whose slot lengths encompass the range of pitched cylindrical apertures  176  and by using thickened, hardened or otherwise stiffened flat washers under the heads of threaded fasteners  174 . 
     Drive wheel  136  is configured and disposed coaxial with wheel support  200 , and is rotatably secured to wheel support  200  by bearings  230  and  198 , which are protected by seals  232  and  202  respectively. Drive wheel shaft  190  extends from a first end  189 , which is coupled to the second end of axle shaft  160  (e.g., by a flexible coupling, shown as half a constant velocity joint  194 ) to a second end  191  which is housed within an extension  204  of wheel support  200 . In doing so, drive wheel shaft  190  projects through an opening  203  within second steering knuckle  166  and an opening  205  within wheel support  200  to engage a bore  228  of a gear  220 , described below. Drive wheel shaft  190  is supported within wheel support  200  by bearing  196 . Constant velocity joint  194  is pivotally flexible but laterally stiff; i.e., is provided only an angular degree of freedom. 
     Final drive  146  is provided to reduce rotational speed of axle shaft  160  and to correspondingly increase torque delivered by axle shaft  160 . Final drive  146  is shown as a planetary gearset disposed within drive wheel  136 , and within and about extension  204  portion of wheel support  200 . Final drive  146  includes a drive or pinion gear, shown as a sun gear  220 , three planet gears  224  and an internal ring gear  226 . In a preferred embodiment, sun gear  220 , planet gears  224  and internal ring gear  226  are coplanar, and include teeth  222  having a conventional spur or helical tooth form. In an alternative embodiment for especially high torque loads, particularly when employing reduction ratios higher than, typically, approximately 10:1, a special tooth form may be necessary to maintain sufficient tooth contact and engagement. 
     Ring gear  226  is affixed to an interior peripheral surface  135  of drive wheel  136  (e.g., by interference fit, discontinuities such as keys and keyways, threaded fasteners, weld or braze, adhesives, etc.). In an alternative embodiment (not shown), a ring gear may be fabricated integral with drive wheel  136 . Planet gears  224  are rotatably secured to wheel support  200  at side openings  206  within extension  204  of wheel support  200 , and rotate upon bearings  236  and planet shafts  234  (shown in FIGS. 7 and 9) affixed thereto. Sun gear  220  is slidingly movable along drive wheel shaft  190  but is rotationally engaged with drive wheel shaft  190  (e.g., by a spline  192  shown, keying, polygonal cross section, etc.). Since drive wheel  136  is secured to wheel support  200  and since wheel support  200  is laterally adjustable in position with respect to second steering knuckle  166 , and since ring gear  226  is secured to drive wheel  136  and planet gears  224  are secured to wheel support  200 , it is necessary for sun gear  220  to be movable upon the length of drive wheel shaft  190  to accommodate a lateral adjustment in position of wheel support  200 . 
     In an alternative embodiment (not shown), sun gear  220  is replaced by gear teeth formed directly on the surface of drive wheel shaft  190  in place of spline  192  shown. 
     FIGS. 4 and 5 show more clearly the relationships between sun gear  220 , planet gears  224  and ring gear  226 . Planet gears  224  are seen to be coplanar with ring gear  226  in FIG. 4, and FIG. 5 shows the meshing relationship of the above gears. While FIGS. 3 and 5 show a quantity of three planet gears  224 , more or fewer may be provided depending upon tooth loading and other conventional design parameters well known to those of skill in the art. 
     FIG. 4 also shows the use of an adapter  208  in adapting and engaging drive wheel  136  to endless track  126 , as well as support structure for endless track  126  and including bogie wheel pivot frame  132 , pivots  210  and pivot pins  212 . 
     FIG. 6 shows an engagement of axle shaft  160  (better seen in FIG. 7) with drive wheel shaft  190  at a flexible coupling  194 , located generally within second steering knuckle  166  (better seen in FIGS. 3,  4 ,  7  and  9 ) and wheel support  200  in the region of steering axis  144  (shown in FIGS.  2  and  3 ). 
     FIG. 7 shows steerable, adjustable-track width track drive  122  in extended position  140 ( b ) (shown in solid lines) and in contracted position  140 ( a ) (shown in phantom lines) with respect to frame  112  (shown in FIGS. 1 and 2) and to axle shaft  160 , axle shaft housing  162 , first steering knuckle  164  and second steering knuckle  166 . Track width “W” of tractor  102  is maximized, as threaded fasteners  174  are disposed within the innermost apertures  176  of wheel support  200  with respect to second steering knuckle  166 . Sun gear  220 , engaged with planet gears  224  supported within wheel support  200  by planet shafts  234  and bearings  236 , has slid along drive wheel shaft  190  to accommodate the extended position of the rest of steerable track drive  122 . Bearings, shown as bushings  170 , facilitate pivotal movement of kingpins  168  coupled between first steering knuckle  164  and second steering knuckle  166 . 
     FIG. 8 shows steerable, adjustable-track width track drive  122  in retracted position  140   a  (shown in solid lines) and extended position  140   b  (shown in phantom lines). Second end  180  of power steering actuator  138  and tie rod end  182  are seen to have been repositioned in cooperation with the repositioning of steerable track drive  122 . In the preferred embodiment, this is accomplished by use of a power steering actuator bracket mounting hole pattern (not shown) which includes a quantity and pitch of mounting holes corresponding to those of apertures  176  in wheel support  200  (shown in FIGS.  3  and  7 ). Cylinder portion  139  of actuator  138  is thereby repositioned in correspondence with steerable track drive  122 . In an alternative embodiment, a rod  184  of actuator  138  is adjusted in length; e.g., by use of adapters and adjustable connections. In another alternative embodiment, the position of second end  180  is changed in cooperation with steerable track drive  122  by changing the volume of hydraulic fluid within cylinder  139 . 
     FIG. 9 shows steerable, adjustable-track width track drive  122  in a contracted position  140   a  (shown in solid lines) with respect to frame  112  (shown in FIGS. 1 and 2) and to axle shaft  160 , axle shaft housing  162 , first steering knuckle  164  and second steering knuckle  166  and fragmentarily in extended position  140   b  (in phantom lines). Track width “W” of tractor  102  is minimized, as threaded fasteners  174  are disposed within the outermost apertures  176  of wheel support  200  with respect to second steering knuckle  166 . Sun gear  220 , engaged with planet gears  224  supported within wheel support  200  by planet shafts  234  and bearings  236 , has slid along drive wheel shaft  190  to accommodate the contracted position of the rest of steerable track drive  122 . Compare FIG. 9 with FIG.  7 . 
     FIG. 10 shows steerable, adjustable-track width track drive  122  steered by actuator  138  in position  140   c  (shown in solid lines) corresponding to a turn of tractor  102  toward left side  110 , and in position  140   e  (shown in phantom lines) corresponding to a turn of tractor  102  toward right side  108 . Steerable track drive  122  is depicted in an extended position  140   b  of track width “W” adjustment (shown in FIGS.  2  and  8 ); comparison with FIG. 8 reveals that a depiction in contracted position  140   a  (shown in FIGS. 2 and 8) would be similar in appearance. 
     Thus, it should be apparent that there has been provided in accordance with the present invention an adjustable track suspension that fully satisfies the objectives and advantages set forth above. Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.