Abstract:
An endless track assembly that mounts to a wheeled vehicle. The assembly provides 1) a track suspension having fixed or adjustable, independently biased sets of idler wheels to vary the track contour without affecting track tension, 2) an eccentric bearing housing at a drive sprocket controls track tension, 3) a contoured peripheral edge at the drive sprocket prevents ice and mud buildup, 4) rubber-coated, plastic idler wheels facilitate track movement, 5) a multi-vehicle compatible adapter mounting plate accommodates a variety of vehicles, 6) a rotation limited torsion coupler and/or rotation limiting coupler arms prevent track contact with the vehicle, 7) a locking steering arm coupler prevents loss of steering control, and 8) shaped track lugs and channels clear and direct debris away from the track suspension and drive assembly. The improved suspension particularly supports sets of idler wheels in pivotal relation to the track support frame and resiliently biases a pre-tensioned rocker arm that links adjacent suspension arms mounted to the adjoining idler wheels. Suspension arm movement induces expansion and contraction of tension springs coupled to the rocker arms to augments shape changes at the track contact surface to optimize traction and steering control.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a continuation of Ser. No. 10/348,156, filed on Jan. 21, 2003, now U.S. Pat. No. 6,904,986. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to all terrain vehicles (ATV) and, in particular, to an improved endless track assembly that can be substituted for the drive wheels of wheeled ATV&#39;s or any two, four or other multi-wheel drive vehicle. 
   A variety of all terrain vehicles have been developed for recreational, commercial, farm and military use. Such vehicles can include wheels and/or endless track assemblies to achieve traction over off-road surfaces with relatively low surface pressure at the contact surfaces of the drive train. 
   Snowmobiles represent an example of a track-based recreational vehicle that is used on snow and ice. The tracks, however, are not readily susceptible to operation over other types of terrain (e.g. abrasive, non-frozen) and use of the vehicle is limited to certain climates and seasons of the year. 
   A variety of other personal ATV&#39;s that support tracks, floatation tires and/or combinations of tires and tracks are also available for year round use over woodland, wet and swampy or desert terrain. The drive trains of the track-based ATV vehicles, like snowmobiles, are typically designed for dedicated use and cannot be readily adapted to alternative uses. Wheel-based ATV vehicles supported on floatation tires work well in woodland conditions, but have difficulty traversing snow, swamp and desert terrain. 
   An economical conversion assembly is therefore desired to expand the operational use of wheel-based ATV&#39;s and pickup trucks. Examples of some track assemblies that can be used to convert 4-wheel drive vehicles to track vehicles are shown at U.S. Pat. Nos. 3,689,123; 4,448,273; and 5,607,210. 
   The present improved track assembly was developed to accommodate the foregoing need and provides a number of improved features that accommodate a wide range of vehicles offered by a number of automotive and ATV manufacturers. Collectively, the improvements permit the conversion of the ATV&#39;s over to track operation in a matter of minutes. 
   The improved track assembly provides 1) a resiliently biased idler wheel suspension that conforms the shape of the track contact surface to terrain changes, 2) rubber coated, plastic idler wheels, 3) a drive wheel with a radiused peripheral edge to prevent ice and mud buildup, 4) an eccentric track tensioner housing that rotates the track drive wheel to control track tension, 5) a multi-vehicle adapter mounting plate, 6) stop limit flanges at a torsion mounting coupler, 7) a set screw restrained coupler arm, and 8) track lugs shaped to direct debris away from the track suspension and drive assembly. 
   SUMMARY OF THE INVENTION 
   It is a primary object of the invention to provide an endless track assembly that can be substituted for a wheel of a wheeled vehicle. 
   It is further object of the invention to provide an improved endless track assembly having an idler wheel suspension that conforms the track contact surface to contour changes in the terrain. 
   It is a further object of the invention to provide a resiliently biased idler wheel suspension that accommodates changing terrain contours without changing the track tension and maintains a relatively small area of ground contact to facilitate steering. 
   It is a further object of the invention to independently and resiliently bias multiple groupings of idler wheels to vary the track contour to maintain track contact with elevated obstructions and depressions and wherein each grouping is independently biased relative to the other groupings. 
   It is a further object of the invention to provide a track suspension with a pair of idler wheels having an adjustable, complementary resilient bias (e.g. compression or extension) such that a constant relative bias can be set and maintained between the idler wheels as the wheels rise and/or fall and correspondingly the track profile changes with contour changes. 
   It is a further object of the invention to provide a track suspension having fore and aft idler wheel sets and wherein the idler wheels are independently biased under compression or extension relative to each other. 
   It is a further object of the invention to provide a track support frame with a replaceable drive wheel having teeth protruding to the lateral sides to accommodate tracks having different pitches between the drive lugs. 
   It is a further object of the invention to provide a drive sprocket having a contoured peripheral edge shaped to direct ice, mud and other debris away from the edge. 
   It is a further object of the invention to provide an eccentric coupling between the frame and track to adjust track tension. 
   It is a further object of the invention to provide an eccentric housing at the drive sprocket that rotates within a mating aperture at the support frame to adjust track tension. 
   It is a further object of the invention to provide molded plastic idler wheels coated at a circumferential surface with a material adhesively complementary to the drive track material (e.g. rubber) to enhance gripping between the idler wheels and drive track and with exposed plastic sidewalls that contact and slip within track channels or grooves to minimize track wear. 
   It is a further object of the invention to provide a drive track wherein the belting and cords at the peripheral edges of the track are constructed to cup inward adjacent the sides of the drive sprocket and idler wheels to prevent detachment of the track from the support frame. 
   It is a further object of the invention to provide a multi-vehicle adapter plate that mounts to the drive sprocket and has shaped surfaces (e.g. contours, holes, slots, recesses, dimples etc.) that mate with different mounting configurations at a number of vehicles. 
   It is a further object of the invention to provide an anti-torque coupler between the track assembly and vehicle having first and second linkage pieces mounted to pivot relative to one another and wherein flanged surfaces at the linkage pieces limit rotation of the track assembly relative to the vehicle. 
   It is a further object of the invention to provide a coupler housing that mounts to a vehicle steering linkage (e.g. tie rod end or ball joint) and contains a setscrew that cooperates with a contoured surface of a mating linkage piece to draw the linkage piece into abutment with the housing and lock the connections to prevent vibration and loosening. 
   The foregoing objects, advantages and distinctions of the invention are obtained in the presently preferred track assembly of the invention. The assembly provides a cast metal support frame having right and left vertical risers and upper and lower cross beams. An aperture at the upper cross beam supports an eccentric housing mounted to a replaceable drive sprocket. The eccentric housing extends through a drive frame aperture and upon rotation induces the drive sprocket to establish the track tension. Flange arms of the frame at the aperture compressively capture the housing and alignment of the drive sprocket to the support frame to maintain an established track tension. 
   Lateral arms project from the drive sprocket and engage drive lugs at the interior of the track. The peripheral edge of the drive sprocket is contoured to prevent the build-up of ice, mud and debris at the drive sprocket and track grooves. Drive sprockets with different tooth spacings can be attached to the frame. 
   A multi-vehicle adapter plate couples the drive sprocket to a vehicle&#39;s lug bolts. Associated suspension linkages couple the track assembly to the chassis and/or steering surfaces of a variety of different vehicles. 
   Sets of independently biased, molded plastic, rubber coated idler wheels cooperate with the drive sprocket to support a lugged drive track. Two sets of differing sized idler wheels bias the forward and trailing ends of the drive track to induce changes in the track contact surface that mimic contour changes in the terrain. 
   Pivot pins secured to the lower cross beam support a pair of suspension or swing arms that support the axles of each set of idler wheel axles. Other pivot pins secure one end of a linkage or rocker arm that extends through a channel or bore in the lower crossbeam between the swing arms. A spring, mounted under compression with a threaded adjuster fitted to the frame, biases the opposite end of the rocker arm. Rotation of either swing arm induced by movement of the idler wheels over an elevated obstruction or into a depression is transferred via the rocker arm to the other idler wheel and is opposed or assisted as determined by a pre-set, adjustable bias at the spring. 
   A torsion control coupler is secured to one of the vertical risers and a pair of linkage pieces extend from a core piece. Flanges at the linkage pieces project to interact as stops to limit the maximum rotation of the track assembly. A steering piece mounts between one of the linkage pieces and a coupler housing that captures the steering linkage of the vehicle, for example a tie rod end. A contoured surface of the steering piece cooperates with a setscrew at the coupler housing to capture and lock the tie rod end against vibration. 
   Shaped lugs project from the track interior to define channels for the plastic idler wheels. Lateral uncoated sides of the idler wheels contact the channel walls and a rubber tread band contacts the track. The lugs scrape debris from the idler wheels and provide surfaces shaped to direct the debris away from the track interior 
   Still other objects, advantages, distinctions and constructions of the invention will become more apparent from the following description with respect to the appended drawings. Similar components and assemblies are referred to in the various drawings with similar alphanumeric reference characters. The description should not be literally construed in limitation of the invention. Rather, the invention should be interpreted within the broad scope of the further appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an assembled front perspective drawing of the track assembly. 
       FIG. 2  is an assembled rear perspective drawing of the track assembly. 
       FIG. 3  is a perspective drawing of the track assembly shown in exploded assembly. 
       FIG. 4  is a perspective drawing of a row of drive lugs at the interior surface of the track. 
       FIG. 5  is a diagrammatic representation showing alternative idler wheel positions and related contour changes at the drive track to accommodate elevated obstructions. 
       FIG. 6  is a diagrammatic representation showing alternative idler wheel positions and related contour changes at the drive track to accommodate depressions in the terrain. 
       FIG. 7  is a diagrammatic representation of a compressively biased idler wheel suspension. 
       FIG. 8  is a diagrammatic representation of an idler wheel suspension biased with springs mounted in extension. 
       FIG. 9  is a plan view showing the peripheral edge shape of the drive wheel relative to a drive channel at the track interior. 
       FIG. 10  is a cross section view showing the peripheral edge shape of an idler wheel relative to a drive channel at the track interior. 
       FIG. 11  is a diagrammatic representation showing alternative track tensions at the drive track at different rotations of the eccentric drive track tensioner. 
       FIG. 12  is a plan view showing the mounting plate adapter. 
       FIG. 13  is a perspective drawing showing a two-section coupler to the torsion control housing. 
       FIG. 14  is a perspective drawing showing a steering arm coupler housing and control arm. 
   

   Similar structure throughout the drawings is referred to with the same alphanumeric reference numerals and/or characters. 
   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1–3 , front, rear and exploded assembly views are shown to the improved track assembly  2  of the invention. Individual track assemblies  2  are typically mounted to the drive and non-drive wheels of an ATV, truck or other vehicle to convert the vehicle over to off road travel over snow, sand and other terrain that requires a relatively low contact surface pressure. The assemblies  2  when adapted to a typical personal ATV provide a contact surface pressure of less than one-pound per square inch. Larger track assemblies  2  can be adapted to automotive vehicles, such as ½ to 1 ton pickup trucks or even larger vehicles. 
   Each track assembly  2  generally provides a reinforced, endless track  6 . The track  6  is typically constructed of rubber with suitable belting and reinforcing fibers to withstand typically encountered terrain, including rocks, logs, mud, sand etc. Exposed lateral, longitudinal, peripheral edges  4  and  5  of the track  6  are constructed to cup slightly inward, upon setting a preferred tension. The cupping of the track edges  4  and  5  in the space adjacent exposed sides of adjoining idler wheels facilitates retention of the track  6  to the suspension. 
   The outer ground contact surface  8  is provided with an array of lugs  10  of desired shapes and sizes that are typically arranged in displaced rows or other desired arrangements. The lugs  10  are generally shaped and located to enhance traction and travel over an anticipated terrain. The inner surface  9  of the track  6  includes a series of rows  12  of laterally displaced inner lugs  14  and outer lugs  16 , reference  FIG. 4 . The lateral separations between the lugs  14  and  16  define a pair of longitudinal idler wheel channels  18  that are displaced from a center longitudinal drive wheel channel  20 . 
   The track  6  is suspended around two forward and two aft idler wheels  22  and  23  and four inner idler wheels  24 . The idler wheels  22 – 24  (eight idler wheels total) are mounted to the lateral sides of a track frame  26  and rotate in the channels  18 . The fore and aft idler wheels  22  and  23  exhibit a larger diameter (e.g. 8 to 12-inches) than the inner idler wheels  24  (e.g. 3 to 6-inches). 
   A rubber tread band or annulus  27  is fitted to the circumferential support surface of each of the idler wheels  22 – 24  to cushion and provide traction with the inner track surface  9 , reference  FIG. 10 . The band  27  can be constructed from a variety of materials and/or may have a contact surface with the tread surface  9  that is, for example, shaped with grooves or projections to facilitate contact, traction and rotation relative to the track  6 . The band  27  can be insert molded with the wheels  22 – 24  or be separately mounted and/or bonded or coated to the wheels  22 – 24 . 
   The idler wheels  22 – 24  are constructed from compression-molded plastic, although can be constructed of other materials and/or can be constructed with other fabrication processes. The idler wheels  22 – 24  run in the channels  18  and the relatively slippery plastic sides of the wheels  22 – 24  lie adjacent the vertical sidewalls of the longitudinal grooves  18 . The plastic slips upon contact with the lugs  10 . The wheels  22 – 24  are relatively intolerant to the adhesion of debris, which is readily discharged from the wheels  22 – 24  and track interior as discussed below. 
   A cast aluminum drive wheel or sprocket  28  rides in the channel  20 . Lateral flange arms  30  project from the sidewalls of a multi-spoked hub  31  and engage the leading surfaces  34  of the lugs  14  and  16  and the drive track  6 . The circumferential edge  29  of the drive wheel  28  is shaped to prevent the buildup of ice and/or debris at the drive wheel  28 , reference  FIG. 9 . The edge  29  is particularly contoured to exhibit a compound-arcuate profile configured from several back-to-back quarter-round surfaces. Several relieves or recesses are formed which cooperate with the channel  20  to dislodge and eject debris. 
   With attention to  FIGS. 4 ,  9  and  10 , the collection of debris is further reduced via a cooperative wiping action that occurs as the flange arms  30  contact each row  12  of lugs  14  and  16 . The leading surface of the adjoining lugs  14  is generally flat and projects orthogonal to the inner track surface  9  to promote contact with the flange arms  30 . The sidewalls of lugs  14  and  16  at the outer and inner channels  18  and  20 , in turn, exhibit tapered surfaces  33  and  35  that flare inward as they rise from the surface  9 . The tapered surfaces  33  of the channel  20  scrape and relieve debris that is released from the peripheral edge  29  of the drive wheel  28 . Recesses  32  at the trailing surfaces of the lugs  14  further relieve debris from the drive wheel  28  and/or interior of the track  6 . 
   The tapered surfaces  33  and  35  at the channels  18 , otherwise, conform to complementary tapered plastic sidewalls at the idler wheels  22 – 24 . Any debris at the idler wheels  22 – 24  is scraped from the sides of the wheels  22 – 24  as the wheels  22 – 24  rotate along the channels  18 . The plastic to rubber contact also provides for less abrasion than experienced with conventional tracks. The leading and lagging vertical walls  34  and  36  of the lugs  16  each exhibit compound tapers that project to a flat apex. The walls  34  and  36  also taper as they extend laterally toward the lateral edge of the track  6  such that debris scraped from the idler wheels  22 – 24  is directed away from the interior of the track  6 . The idler wheels  22 – 24  are thus able to run smooth without collecting debris and possibly dislodging the track  6  from the frame  26 . 
   Returning attention to  FIG. 3  and although only two of the eight idler wheels  22 – 24  are shown, each track assembly  4  is constructed to resiliently bias the idler wheels  22 – 24  to follow and conform the track  6  to contour changes in the terrain. In a resting condition (shown in dashed line), the track frame suspension supports the track  6  to the frame  26  to exhibit a generally isosceles triangular-shaped longitudinal profile or contour, reference  FIGS. 5 and 6 . During motion, the idler wheels  22 – 24  independently and resiliently allow the forward, middle and aft end portions of the track&#39;s ground contact surface  8  to flex and undulate. 
   The longitudinal profile or contour of the track  6  is directed by the idler wheels to maintain steering control and optimal contact with the terrain such as shown in solid line at  FIGS. 5 and 6 . This is achieved by independently biasing the forward and aft sets of the idler wheels  22 , 24  and  23 , 24  relative to each other. The preset bias of each set of idler wheels  22 , 24  and  23 , 24  is separately adjusted to allow the user to tailor the ride of each track assembly  4 . 
   Movement of the contact surface  8  over an elevated obstruction or into a depression induces the forward idler wheels  22  and the adjacent idler wheels  24  to rotate and change the track contour. For example and with attention to  FIG. 5 , if the forward idler wheels  22  rise and rotate clockwise relative to the frame  26 , the adjacent idler wheels  24  are directed to follow clockwise by a rocker arm linkage  78 . A resilient biasing member  86  expands and biases the rocker arm  78  to assist the rotation and maintain track contact with the ground. 
   Alternatively and with attention to  FIG. 6 , if the forward idler wheels  22  follow a depression and rotate counterclockwise relative to the frame  26 , the following idler wheels  24  are directed to follow by the rocker arm  78 . The biasing member  86  is simultaneously compressed to resist the rotation. In either instance, the area of the contact surface  8  with the terrain is resiliently optimized, which promotes traction and steering control. The adjacent aft set of idler wheels  23  and  24  are similarly biased to ensure track contact. 
   The forward set of two idler wheels  22  and two adjacent inner idler wheels  24  are mounted to pivot about the frame  26  and are resiliently biased with an adjustable, resilience preset by a spring member  86  on the rocker arm  78 . The two aft idler wheels  23  and two adjacent inner idler wheels  24  are mounted to independently pivot about the frame  26  and are biased with a separately adjusted, bias member  86  abutting the rocker arm  78 . As the contact surface  8  negotiates the terrain, the leading and lagging sets of idler wheels  22 ,  24  and  23 , 24  cooperate to induce the track  6  to conform to the terrain. 
   The manner of mounting the idler wheels  22 – 24  and drive wheel  28  to the drive frame  26  is apparent from  FIG. 3 . The frame  26  provides forward and aft vertical riser members  42  and  44 . Upper and lower cross members  46  and  48  connect the riser members  42  and  44 . The idler wheels  22 – 24  are secured to the lower cross member  48  and the drive wheel  28  is secured to the upper cross member  46 . The mechanical construction and suspension of each of the forward and aft sets of idler wheels  22 ,  24  and  24 ,  23  is identical and is described below for only one side of the forward set of wheels  22 ,  24 , but should be understood to be the same for the aft set. 
   The forward idler wheels  22  are secured to the bottom of the riser member  42  with an outer suspension arm  50  and a pivot pin  52 . Zerk fittings  51  are mounted to the pin  52  to facilitate lubrication of the pivot. The pivot pin  52  extends through apertures  54  in a pair of outer swing arms  56  that extend from a bushing piece  58  and a bore  60  at the riser member  42 . The swing arms  56  mount to the lateral sides of the riser member  42 . An axle  62  extends through a bore  64  of the bushing piece  58 , seals  57  and bearings  59  and supports the forward idler wheels  22 . 
   The inner idler wheels  24  are secured to the bottom of the riser member  42  with a suspension arm  66  and another pivot pin  52  outfitted with a zerk fitting. The pivot pin  52  extends through apertures  70  in a pair of swing arms  72  that extend from a bushing piece  74  of the suspension arm  66  and align with a bore  76  at the riser member  42 . The swing arms  72  mount to the lateral sides of the riser member  42 . An axle  62  extends through a bore  77  of the bushing piece  74 , seals  57  and bearings  59  and supports the inner idler wheels  24 . 
   A link arm or rocker arm  78  mounts through a vertical aperture  47  in the cross member  48  and is secured between and to the swing arms  56  and  70  with pivot pins  52  that don&#39;t contain zerk fittings. The pivot pins  52  particularly mount between apertures  82  and  84  at the swing arms  56  and  72  and bores  79  and  81  at the rocker arm  78 . Forces exerted on either of the pairs of idler wheels  22  or  24  relative to the frame  26  is transferred by the rocker arm  78  to the adjoining set of idler wheels. 
   A spring  86  is mounted in a bore  88  of the riser member  42  and is contained between an end cap  92  that is secured to the bore  88  and a seat  90  at the link arm  78 . A pre-loaded condition of either tension or compression of the spring  86  is established with a bolt  93  that extends through the riser  42  and contacts the cap piece  92 . Any movement of the idler wheels  22 ,  23  or  24  is thus opposed or assisted in relation to the compression or expansion of the spring  86  in relation to the pre-loaded condition. As the longitudinal profile or contour of the track  6  changes to conform to the terrain, the track tension however does not change with movement of the idler wheel suspension. 
     FIGS. 7 and 8  separately depict in diagrammatic form two generalized alternative ways to bias the grouped sets of idler wheels  22 , 24  and  23 , 24 .  FIG. 7  demonstrates the compressive mounting of the spring  86  shown and used in the preferred embodiment of the assembly  2  and discussed with respect to  FIGS. 3 ,  5  and  6 .  FIG. 8  demonstrates a mounting of the spring  86  in extension relative to an intermediate turnbuckle or anchor piece  87 . Opposite hooked ends of the turnbuckle  87  are independently adjusted to vary the static extension and resilient bias on the springs  86  and the forward and aft sets of idler wheels  22 , 24  and  23 , 24 . 
   With continuing attention to  FIG. 3  and additional attention to the diagrammatic  FIG. 11 , the tension of the track  6  relative to the idler wheels  22 – 23  and drive wheel  28  is separately established with an eccentric mounting of the drive wheel  28  to a bore  94  at the upper cross member  46 . The track tension is particularly established with an eccentric assembly  100  that rotates within the bore  94 . 
   The assembly  100  includes a hub  101  that mounts through a seal  103  and bolts to the drive sprocket  28  with fasteners  119 . An eccentric shaped bearing housing  104  having a bore  117 , that is drilled off-center to provide an eccentric surface, extends from the hub  101  and rests in the bore  94 . A separate, cylindrical spindle bearing  106  is secured in the bore  117  of the housing  104  with a snap ring  105 . The housing  104  and spindle bearing  106  are retained to the hub  101  with a washer  107  and nut  109 . A cover or lock cap  99  and seal  97  are secured to the end of the housing  104  with a number of fasteners  15 . 
   Upon loosening carriage fasteners  15  at flanges  91  that depend from the frame  26  at the bore  94  and beneath the cap  99  and rotating the cap  99  with a wrench  95 , the housing  104  rotates around the spindle bearing  106  within the bore  94  and the drive sprocket  28  is moved. Depending upon the relative rotation of the eccentric housing  104 , which rotates in eccentric relation to the spindle bearing  106 , the drive sprocket  28  stretches or relaxes the tension of the track  6 . Once a preferred track tension is established, the fasteners  15  are tightened to draw the frame  26  at the bore  94  into compression with the bearing housing  104  to fix the tension on the track  6 . It is to be appreciated a variety of other fastening arrangements may be used to secure the established position of the bearing housing  104 . 
   The track assembly  2  is typically secured to the vehicle at available lug bolts that extend from the vehicle wheel and mount to holes  108  at the hub  101 . Due to the wide range of vehicles with which the assembly  2  is compatible, a special adapter plate  110  is provided to facilitate mounting the track assembly  2  to each of the vehicles. A presently preferred plate  110  is shown at  FIG. 12  and mounts between the hub  101  and the vehicle drive train, typically the driven or un-driven hubs of a converted vehicle. The adapter plate  110  is held to the hub  101  with a number of fasteners  113 . Any number of apertures  112 , slots  116  and/or raised surfaces  118  or depressions  120  can be provided at the adapter plate  110  to align with a particular mounting geometry of a vehicle. The adapter plate  110  has particularly been designed to mount to several different lug bolt arrangements of identified ATV&#39;s and allow clearance over protruding brake inspection covers and other adjoining vehicle parts. 
   Returning attention to  FIG. 3  and with additional attention to  FIG. 13 , the track assembly  2  is separately secured to the vehicle with a torsion control assembly  122  to limit the relative rotation of the track assembly  2  to the vehicle. A pair of coupler arms  121  and  123  or improved coupler arms  124  and  126  are secured to the assembly  122 . The arms  123  and  124  are secured to a pair of brackets  138  with fasteners  125 . The coupler brackets  138  contain resilient or elastomer shims  140 . The arms  121  and  126  are separately secured to a cooperating steering or stationary surface at the vehicle. 
   A torque tube  142  extends from an appropriate one of two apertures  144  in the risers  42  and  44  and is secured to the drive frame  26  with bolt and nut fasteners  141  and  143 . The torque tube  142  might also be secured to the risers  42  and  44  with a variety of alternative fasteners. For example, the tube  142  might include spring pins or other projections that snap into mating apertures or recesses provided at the apertures  44 . 
   An outer section of the torque tube  142  nests in the shims  140 . A flared outer end of the torque tube  142  retains the torque tube  142  at an equilibrium condition in the brackets  138 . Clockwise and counterclockwise Rotation of the torque tube  142  is resisted by the shims  140  and thereby prevents contact between the track assembly  2  and the vehicle. 
   Where the coupler arms  124  and  126  of  FIG. 13  are used to couple the track assembly  2  to a vehicle, stop flanges  128  and  130  are provided to limit the maximum rotation of the track assembly  2 . That is, the stop flanges  128  and  130  limit rotation of the arm  126  relative to the surfaces  132  and  134  at the arm  124 . As the arms  124  and  126  normally rotate, the flanges  128  and  130  contact the surfaces  132  and  134  to prevent over-rotation of the assembly  2  relative to the assembly  122  and contact with the vehicle. 
   Where the arm  126  couples to a steering surface of the vehicle, such as a tie rod end, an improved locking coupler  150  shown at  FIG. 14  is mounted to the arm  126 . The coupler  150  prevents possible loosening of the critical steering connection. The coupler  150  provides a housing  152  having a locking bar  154  that is welded to the housing  152 . The housing  152  captures the vehicle&#39;s tie rod end to the end of a steering arm  155  that separately connects to a vehicle steering surface. The configuration of the housing  152  and arm  154  can be varied to accommodate different types of tie rods. 
   The housing  152  is typically secured to the vehicle with a fastener between an aperture  156  at the locking arm  154  and the aperture  146  of the coupler arm  126 . A vehicle tie rod end (not shown) mounts through an aperture  158  in the housing  152 , which can be hexagonal shaped and/or include flat surfaces that align with flat surfaces at the tie rod end, and an aperture  160  in the vehicle steering arm  155 . 
   The connection is locked or prevented from loosening upon separately securing a setscrew  162  at the locking bar  154  to contact a surface  164  of the arm  155  and draw the arm  154  and the tie rod end to the housing  152 . A nut (not shown) separately secures the tie rod to the housing  152 . An additional brace (not shown) may also be fitted between the housing  152  and adjoining suspension components of the vehicle to help support the steering arm  155 . 
   While the invention has been described with respect to a number of preferred constructions and considered improvements or alternatives thereto, still other constructions may be suggested to those skilled in the art. It is also to be appreciated that selected ones of the foregoing features, for example, the independently biased idler wheel suspension, contoured drive sprocket, eccentric tensioner, rotation limited torsion coupler and/or steering coupler arms, can be used singularly or can be arranged in different combinations to provide a variety of improved track assemblies. The foregoing description should therefore be construed to include all those embodiments within the spirit and scope of the following claims.