Abstract:
A tensioning device is provided for maintaining the tension on a continuous flexible track of a track apparatus. The track apparatus includes an idler wheel which engages the flexible track and which is movable between a first non-deflected position and a second deflected position. A dampening mechanism extends between an idler axle which supports the idler wheel and the frame of the track apparatus in order to exert a force on the idler axle to urge the idler wheel towards the non-deflected position. The dampening mechanism progressively increases the force on the idler axle as the idler wheel moves towards the deflected position.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to track apparatus for vehicles. In particular, this invention relates to track apparatus of the type for use in place of a vehivle wheel and, more particularly, to apparatus for maintaining proper tension on flexible tracks during operation. 
     BACKGROUND OF THE INVENTION 
     Agricultural vehicles such as tractors, combines and the like are commonly used in agricultural fields for a variety of jobs, and construction vehicles and other large work vehicles are used for many different jobs on a variety of ground surfaces. Typically, these vehicles have tires on which the vehicles are supported on the ground. These kinds of large vehicles are quit heavy, and their weight is distributed to a relatively small area by the vehicle tires. As a result, the tires of such vehicles tend to compact the soil in the fields or other ground surfaces. Compacted soil discourages growth of crops planted in the fields with need loose soil to flourish, and ground surface compaction is often undesirable for other reasons as well. 
     In addition, since fields and other work sites are often wet due to rain or watering, vehicles which enter the fields become bogged down in the mud due to the fact that there is such a small area in contact with the ground. Therefore, it is highly desirable to develop a track apparatus for vehicles which spreads vehicle weight over a larger area so as to reduce the degree of ground compaction. Providing a larger ground-surface engagement area also serves to prevent vehicles from becoming bogged down in mud or other soft ground surfaces. 
     Prior track systems for vehicles is disclosed in U.S. Pat. Nos. Re36,284 (Kelderman) and 5,829,848 (kelderman), assigned to the assignee of the present invention and incorporated herein by reference. The Kelderman ′284 reissue and ′848 patents disclose track suspension systems for vehicles having a frame and a continuous rubber track. The drive wheel is attached to the frame for engaging and driving the continuous flexible track. 
     In order to insure proper operation of such track apparatus, the tension on the flexible track must be maintained within a predetermined range. Both a lack of sufficient tension and excessive tension are problematic. 
     By way of example, a minimum tension must be maintained on the flexible track to prevent slippage thereof during operation of the track apparatus -- i.e., inconsistent engagement of the track with leading and trailing idler wheels. Improper track tension is problematic in operation and leads to misalignment and premature wear of the flexible track may result in a loss of horsepower and premature wear of the track. 
     Furthermore, the flexible track of such track apparatus encounters obstacles (e.g. rocks) and other ground-surface irregularities during operation. It is important that the track accomodate irregularities and sudden shocks in order to maintain acceptable operational tension: (1) the matter of maintaining proper tension under normal operation conditions and (2) the ability to accommodate obstacles and the like. 
     While proper track apparatus have tensioning devices, such tensioning devices have problems and shortcomings in their ability to maintain proper tension in a wide variety of surface conditions. There is a need for improved tensioning apparatus to maintain proper track tension and better accommodate obstacles and a variety of surface irregularities during operation. 
     OBJECTS OF THE INVENTION 
     It is an object of this invention to provide an improved track apparatus, of the type for use in place of a vehicle wheel, which overcomes some of the problems and shortcomings of the prior art, including those referred to above. 
     More particularly, it is an ovject of this invention to provide an improved track tensioning apparatus which overcomes the problems and shortcomings of the prior art referred to abovr. 
     Another object of the invention is to provide a track apparatus which maintains a predetermined tension on the track in a variety of use conditions. 
     Another object of this invention is to provide a track tensioning apparatus which avoids or minimizes track “slippage” and misalignment during use. 
     Another object of the invention is to provide an improved track tensioning apparatus which better accommodates a wide range of track deflection of the track, caused by a variety of obstacles. 
     A still further object of the invention is to provide a track apparatus with a tensioning device which is simple, inexpensive to manufacture and maintain, and independent of the vehicle. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, a tensioning device is provided for maintaining proper tension on a continuous flexible track utilized on a track apparatus of the type mountable on the rotatable axle of a vehicle. 
     The track apparatus includes: a frame; a drive wheel structure rotatably mounted with respect to the frame, the drive wheel having an upper circumferential portion engaging the inner surface of a flexible track along the upper length thereof and a lower circumferential portion spaced above the lower length of the track; and leading and trailing idler assemblies having idler wheels engaging the track. The tensioning device includes a dampening mechanism which extends betwee an idler assembly and the frame for exerting a force on the idler axle so as to urge the idler wheel towards the non-deflected position. The dampening mechanism provides force on the idler axle as the idler wheel moves towards the deflected position. The idler assembly includes an idler axle support pivotably mounted to the frame. The idler axle extends through the idler axle support. 
     The tensioning device of this invention includes a main-cylinder housing interconnected to the frame. The main-cylinder housing extends along an axis and defines a main cylinder chamber therein. A main position has a first end pivotably connected to the leading idler wheel assembly and a second end slidably received within the main-cylinder chamber. The main piston is movable between a first extended position in response to the idler wheel being in a non-deflected position and a second retracted position in response to the idler wheel being in the deflected position. A primary dampening structure discourages movement of the main piston toward the retracted position for a first predetermined axial length. A secondary dampening structure discourages movement of the main piston toward the retracted position for a second predetermined axial length. 
     The primary dampening structure includes a primary-dampening cylinder which extends along an axis and defines a primary chamber therein. A primary-dampening piston is slidably received within the primary-dampening cylinder and is movable axially between a first position and a second position. The primary-dampening piston divides the primary-dampening chamber into a first portion for receiving a pressurized gas and a second portion. A fluid conduit interconnects the second portion of the primary-dampening chamber and the main-cylinder chamber. A fluid is disposed within the second portion of the primary-dampening chamber; the main-cylinder chamber, and the fluid conduit therebetween. 
     Similarly, the secondary dampening structure includes a secondary-dampening cylinder extending along an axis and defining a secondary-dampening chamber therein. A secondary-dampening piston is slidably received in the secondary-dampening cylinder and is movable axially between a first position and a second position. The secondary-dampening piston divides the secondary-dampening chamber into a first portion for receiving a pressurized gas and a second portion. The fluid conduit also interconnects the second portion of the secondary-dampening chamber and the main-cylinder chamber. In addition, the fluid is also disposed in the second portion of the secondary-dampening chamber. 
     It is contemplated that the pressure of the pressurized gas in the first portion of the secondary-dampening chamber is greater than the pressure of the pressurized gas in the first portion of the primary-dampening chamber. A limiter may be provided within the primary-dampening cylinder for limiting movement of the primary-dampening piston. 
     The tensioning device may include a manifold having an input, a first output connected to the input of the secondary-dampening cylinder, and a second input connected to the input of the secondary-dampening cylinder. The fluid conduit interconnects the input of the manifold and the main-cylinder chamber. The fluid is disposed within the fluid conduit for travel between the second portion of the primary-dampening chamber, the second portion of the secondary-dampening chamber, and the main-cylinder chamber. 
     In accordance with a still further aspect of the present invention, the tensioning device a main cylinder housing interconnected to the frame of the track apparatus, such main-cylinder housing extends along an axis and defining a main-cylinder chamber therein. A main piston has a first end pivotably connected to the idler wheel and a second end slidably received within the main-cylinder chamber, and is movable between a first retracted position and a second extended position. A dampening mechanism which is mounted at a position remote from the main piston is operatively connected to the second end of the main piston and provides a force for discouraging movement of the main piston toward the retracted position. Such remote dampening mechanism progressively increases the force on a second end of the main piston as the main piston moves toward the retracted position. The remote dampening mechanism may include primary and secondary dampening as described above. 
     In accordance with a still further aspect of the present invention, a track apparatus is provided having the improved tensioning apparatus as described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings furnished herewith illustrate a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the following description of the illustrated embodiment. 
     FIG. 1 is a rear isometric view of a track apparatus for a vehicle incorporating a drive wheel in accordance with the present invention. 
     FIG. 2 is a front isometric view of the track apparatus. 
     FIG. 3 is a front isometric view of the track apparatus with the flexible track removed. 
     FIG. 4 is a front elevation of the track apparatus. 
     FIG. 5 is a fragmentary front elevational, partially in section, of the track apparatus. 
     FIG. 6 is a schematic view of the belt tensioning device of the track apparatus, such device being shown in a first extended position. 
     FIG. 7 is a schematic view of the belt tensioning device in a second intermediate position. 
     FIG. 8 is a schematic view of the belt tensioning device in a third retracted position. 
     FIG. 9 is a graphical representation of the displacement of the belt tensioning device in response to the force thereon. 
     FIG. 10 a  is a cross-sectional view taken along line  12   a - 12   a  of FIG.  4 . 
     FIG. 10 b  is a vross-sectional view taken along line  12   b - 12   b  of FIG.  4 . 
     FIG. 11 is a rear isometric view of the frame of the track apparatus of FIG.  1 . 
     FIG. 12 is a front isometric of the frame. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-2, a track system is generally designated by the reference numeral  10 . In a preferred embodiment, the track apparatus  10  is mounted on an axle (not shown) of an agricultural vehicle such as a tractor or combine. However, it is contemplated as being within the scope of the present invention for track apparatus  10  to be mounted on other types of vehicles such as trucks, automobiles, and the like. 
     Track apparatus  10  includes a drive wheel  12  which mountable to the axle of a vehicle for rotational movement therewith in order to drive a flexible track  15 . As best seen in FIG. 1, in the preferred embodiment, it is intended to mount track apparatus  10  to a vehicle having a planetary axle. However, it is contemplated to mount track system  10  to a bar axle or other type of axle without deviating from the scope of the present invention. 
     Referring to FIG. 2, drive wheel  12  includes a first set of circumferentially spaced attachment openings  18  therein which are aligned with corresponding openings formed in an attachment flange extending radially from the axle of the vehicle, as is conventional. Bolts extend through attachment openings  18  in drive wheel  12  and through corresponding openings in the attachment flange of the axle and are secured by corresponding nuts threaded on the ends thereof in order to interconnect the axle of the vehicle to drive wheel  12  so as to allow drive wheel  12  to rotate in unison with the axle of the vehicle. 
     As best seen in FIGS. 1-3, drive wheel  12  includes an inner wall or side-surface  20  and an outer wall or side-surface  22  interconnected by a radially outer rim  24 . Outer rim  24  includes a plurality of circumferentially spaced openings  26  therein for allowing debris which may accumulate on the inner surface  28  of flexible track  15  to pass therethrough. As shown in FIG. 10, outer rim  24  further includes an outer surface  29  having a plurality of circumferentially spaced drive members  30  projecting radially therefrom. As hereinafter described, drive members  30  are intended to engage corresponding track lugs  32  projecting inwardly from the inner surface  28  of flexible track  15  in order to drive flexible track  15 . 
     As best seen in FIGS. 11-12, track apparatus  10  further includes frame  34  of a uni-body construction. Frame  34  includes first and second side portions  36  and  38 , respectively, which define a drive wheel receipt well  40  therebetween for receiving drive wheel  12 . Side portions  36  and  38  of frame  34  are interconnected by front and rear end panels  42  and  44 , respectively. 
     Side portion  36  includes first and second upper panels  46  and  48 , respectively, which extend laterally from outer surface  50  of generally tubular spindle hub  52  and a lower panel  53 . Side panel  56  interconnects first sides  46   a  and  48   a  of upper panels  46  and  48 , respectively, and first side  53   a  of lower panel  53 . Side panel  54  projects from second sides  46   b  and  48   b  of upper panels  46  and  48 , respectively, and is joined to second side  53   b  of lower panel  53 . A support member  60  extends between outer surface  54   b  of side panel  54  and lower surface  62  of lower panel  53  to add strength and stability to side panel  54  during operation of track system  10 . In the preferred embodiment, support member  60  takes the form of a gusset, but other configurations are possible without deviating from the scope of the present invention. Side panel  54  includes leading and trailing apertures  64  and  66 , respectively, therethrough for receiving corresponding leading and trailing bogie axles, respectively, as hereinafter described. Reinforcement elements  64   a  and  66   a  may be mounted on outer surface  54   b  of side panel  54  about corresponding apertures  64  and  66 , respectively, to reinforce apertures  64  and  66  and prevent deformation of the same by the bogie axles received therein. 
     Side portion  38  of frame  34  includes generally tubular, forward and rearward arms  70  and  72 , respectively. Forward arm  70  includes a first end  74  which is joined to front end panel  42 . Similarly, rearward arm  72  includes a first end  76  joined to rear end panel  44 . Second ends  78  and  80  of forward and rearward arms  70  and  72 , respectively, are interconnected to the upper surface  82  of a generally horizontal base plate  84 . Base plate  84  includes an inner edge  86  directed towards drive wheel receipt well  40  and an outer edge  88 . Side panel  90  depends from inner edge  86  of base plate  84  and includes leading and trailing apertures  92  and  94 , respectively, therethrough for receiving corresponding leading and trailing bogie axles, as hereinafter described. Leading aperture  92  in side panel  90  of side portion  38  is axially aligned with leading aperture  64  in side panel  54  of side portion  36 . Likewise, trailing aperture  94  in side panel  90  of side portion  38  is axially aligned with trailing aperture  66  in side panel  54  of side portion  36 . Reinforcement elements  92   a  and  94   a  may be mounted on outer surface  90   b  of side panel  90  about corresponding apertures  92  and  94 , respectively, to reinforce apertures  92  and  94  and prevent deformation of the same by the bogie axles received therein. Outer surface  90   b  of side panel  90  of side portion  38  is innerconnected to the lower surface  98  of base plate  84  by a support structure  100  to add strength and stability to side panel  90 . In the preferred embodiment, support member  100  takes the form of a gusset, but other configurations are possible without deviating from the scope of the present invention. 
     A leading bogie axle  99  extends through leading aperture  64  in side panel  54  and through leading aperture  92  in side panel  90 . Leading bogie wheels  101  are mounted on rims  103 , FIGS. 1-2, in a conventional manner which, in turn, are mounted on corresponding ends of leading bogie axle  99  in a conventional manner for rotational movement therewith. The outer surfaces  101   a  of leading bogie wheels  101  engage the inner surface  28  of flexible track  15 . Similarly, a trailing bogie axle  105  extends through trailing aperture  66  in side panel  54  and through trailing aperture  94  in side panel  90 . Trailing bogie wheels  107  are mounted on rims  109  (see FIGS. 1-2) in a conventional manner which, in turn, are mounted on opposite ends of trailing bogie axle  105  in conventional manner for rotational movement therewith. The outer surfaces  107   a  of trailing bogie wheels  107  engage the inner surface  28  of flexible track  15 . 
     Inner surface  54   a  of side panel  54  of side portion  36  is interconnected to inner surface  90   a  by leading and trailing bogie axle shrouds  102  and  104 , respectively. Leading bogie axle shroud  102  is generally arcuate in shape and has a first end positioned adjacent leading aperture  64  in side panel  54  of side portion  36  and a second opposite end  102   b  adjacent leading aperture  92  in side panel  90  of side portion  38  so as to partially surround leading bogie axle  99 . First and second spaced mounting flanges  95  and  97  project from leading bogie axle shroud  102 . Mounting flanges  95  and  97  include corresponding openings  95   a  and  97   a , respectively, therein for reasons hereinafter described. Trailing bogie axle shroud  104  is arcuate in shape and includes a first end positioned adjacent to trailing aperture  66  in side panel  54  of side portion  36  and a second end  104   b  positioned adjacent trailing aperture  94  in side panel  90  of side portion  38  so as to partially surround trailing bogie axle  105 . 
     Frame  34  further includes a trailing idler axle support arm  110  which extends between trailing bogie axle shroud  104  and rear end panel  44 . Trailing idler axle support arm  110  includes a generally tubular trailing idler axle support  112  having an inner surface  114  for rotatably supporting trailing idler axle  116 . Trailing idler wheels  117  are mounted on rims  118  (see FIGS. 1-2) in a conventional manner which, in turn, are mounted on corresponding ends of trailing idler axle  116  in a conventional manner for rotational movement therewith. Trailing idler wheels  117  include radially outer surfaces  117   a  for engaging the inner surface  28  of flexible track  15 . 
     Frame  34  further includes a leading idler axle support arm  120  depending from front end panel  42 . Referring to FIGS. 5 and 10 a - 10   b , leading idler axle support arm  120  has a generally tubular terminal end  122  having an inner surface  124  defining a passageway  126  therethrough. Leading idler axle support  130  is pivotally mounted to leading idler support arm  120  by mounting pin  132  extending through passageway  126  in terminal end  122 . Leading idler axle support  130  includes a leading idler axle passageway  134  for allowing leading idler axle  136  to pass therethrough. Leading idler axle  136  includes a notch  136   a  formed therein for allowing piston shaft  139  of cylinder  142  to extend therepast. 
     As is conventional, leading idler axle  136  supports leading idler wheels  137  on opposite ends thereof. Leading idler wheels  137  are mounted on rims  138  which, in turn, are mounted on corresponding ends of leading idler axle  136  in a conventional manner for rotational movement therewith. It is contemplated to provide bearings  141  between rims  138  and corresponding ends of leading idler axle  136  to facilitate rotation of leading idler wheels  137  thereabout. Leading idler wheels  137  include a radially outer surface  137   a  for engaging the inner surface  28  of flexible track  15 . 
     Leading idler axle support  130  further includes a first and second piston mounting ears  140   a  and  140   b  depending therefrom. Each mounting ear  140   a  and  140   b  includes a corresponding aperture  142   a  and  142   b , respectively, therethrough to accommodate piston shaft mounting pin  144 . Apertures  142   a  and  142   b  in piston shaft mounting ears  140   a  and  140   b , respectively, are axially aligned. Piston shaft mounting ears  140   a  and  140   b  define a piston receipt cavity  146  therebetween for receiving terminal end  148  of piston shaft  139 . As best seen in FIGS. 6-8, terminal end  148  of piston shaft  139  includes an opening  150  for receiving mounting pin  144  such that piston shaft  139  of cylinder  142  may pivot on mounting pin  144 . 
     Referring to FIGS. 6-9, main piston shaft  139  includes a second opposite end  154  received within chamber  156  within cylinder housing  158  of cylinder  142 . Cylinder housing  158  includes a first open end  159  for allowing piston shaft  139  to be inserted within main-cylinder chamber  156  and an opposite closed end  160 . Inner surface  162  of cylinder housing  158  forms a slidable interface with the outer surface  164  of piston shaft  139 . Closed end  160  of cylinder housing  158  includes a dog ear having an opening  166  passing therethrough. Closed end  160  of cylinder housing  158  is positioned between mounting flanges  95  and  97  (see FIG. 11, as well as FIGS. 4 and 5) such that opening  166  in closed end  160  is aligned with openings  95   a  and  97   a  in mounting flanges  95  and  97 , respectively. Pin  168  (see FIG. 5) extends through openings  95   a  and  97   a  in mounting flanges  97  and  99 , respectively, and through opening  166  in closed end  160  of cylinder housing  158  so as to pivotally connect cylinder  142  to frame  34 . 
     Referring once again to FIGS. 6-8, chamber  156  within cylindrical housing  158  communicates with input  169  of manifold  170  through conduit  172 . As best seen in FIGS. 4,  11  and  12 , conduit  172  extends through opening  174  in lower panel  53  of side portion  36  of frame  34  and through opening  176  in upper panel  48  of side portion  36  of frame  34 . In a preferred embodiment, manifold  170  is mounted to upper surface  178  of upper panel  48 . Manifold  170  includes a first output  180  operatively connected to the input  182  of low pressure cylinder  184  and a second output  186  operatively connected to the input  188  of high pressure cylinder  190 . Seals  192  are provided between the outputs  180  and  186  of manifold  170  and the inputs  182  and  188  of cylinders  184  and  190 , respectively, to maintain the integrity of the connections therebetween. 
     Primary-dampening cylinder  184  includes an inner surface  194  defining a primary-dampening chamber  196  therein. A primary-dampening piston  198  is slidably received within chamber  196  so as to divide chamber  196  into a first portion  196   a  for receiving low pressure nitrogen gas therein and a second portion  196   b  which communicates with chamber  156  within cylinder housing  158  through manifold  170  and conduit  172 . A generally tubular limiter member  200  is positioned within chamber  196 . Limiter member  200  includes an outer surface  202  which engages the inner surface  194  of cylinder  184 . Limiter member  200  limits movement of piston  198  such that piston  198  is slidable between a first position (see FIG. 6) and a second position (see FIGS.  7  and  8 ). 
     Secondary-dampening cylinder  190  includes an inner surface  204  defining a secondary-dampening chamber  206  therein. A secondary-dampening piston  208  is slidably received within chamber  206  so as to divide chamber  206  into a first portion  206   a  for receiving a high pressure nitrogen gas therein and a second portion  206   b  which communicates with chamber  156  within cylinder housing  158  through manifold  170  and conduit  172 . It is contemplated to provide a fluid within chamber  156  of cylinder housing  158 , conduit  172 , manifold  170 , and second portions  196   b  and  206   b  of chambers  196  and  206 , respectively, in cylinders  184  and  190 , respectively. 
     As main piston shaft  139  moves into main-cylinder chamber  156  of cylinder housing  158 , from left to right in FIGS. 6-8, fluid is urged from chamber  156  through conduit  172  into manifold  170 . Given that the first portion  196   a  of primary-dampening chamber  196  of cylinder  184  is filled with a low pressure nitrogen gas and that the first portion  206   a  of secondary-dampening chamber  206  of cylinder  190  is filled with a high pressure nitrogen gas, the fluid within manifold  170  will take the path of least resistance and urge piston  198  within chamber  196  from right to left in FIGS. 6-8 against the bias of the low-pressure nitrogen gas in first portion  196   a  of chamber  196  in cylinder  184 . Travel of piston  198  within chamber  196  is terminated when piston  198  engages limiter member  200  (see FIG.  7 ), which corresponds to a predetermined distance X which piston shaft  139  is inserted into chamber  156  of cylinder housing  158  (see FIG.  9 ). Thereafter, as piston shaft  139  is further inserted into chamber  156  of cylinder housing  158 , the fluid within manifold  170  will attempt to urge piston  208  against the force of the high pressure nitrogen gas present in first portion  206   a  of chamber  206  of second cylinder  190  (see FIG.  9 ). 
     Referring to FIG. 9, the amount of force necessary to insert main piston shaft  139  a predetermined distance within chamber  156  of cylinder housing  158  gradually increases from an initial value A to an increased value A′ as the low pressure nitrogen gas is compressed in first portion  196   a  of primary-dampening chamber  196  in cylinder  184  by piston  198  being urged from the first to the second position by the fluid. Thereafter, the amount of force necessary to further insert piston shaft  139  a second predetermined distance Y-X within secondary-dampening chamber  156  of cylinder housing  158  gradually increases from an initial value B to an increased value B′. Since the nitrogen gas within secondary-dampening cylinder  190  is under greater pressure than the nitrogen gas within primary-dampening cylinder  184 , a substantially greater force is required for piston shaft  139  to travel the predetermined distance Y-X than the initial predetermined distance X. 
     In operation, track apparatus  10  is mounted to an axle of a vehicle through drive wheel  12  as heretofore described. The axle of the vehicle is rotated in a conventional manner through the vehicle by its engine and through a transmission which can vary the speeds and allow for forward and reverse rotation. Flexible track  15  of track apparatus  10  is positioned over drive wheel  12  such that lugs  32  projecting from the inner surface  28  of flexible track  15  are received between corresponding pairs of drive members  30  projecting from outer surface  29  of outer rim  24  of drive wheel  12 . As drive wheel  12  rotates, drive members  30  engage corresponding track lugs  32  and drive flexible track  15  about drive wheel  12 . Thereafter, successive drive lugs  30  engage subsequent track lugs  32  extending from the inner surface  28  of flexible track  15  so as to drive flexible track  15  about drive wheel  12 . 
     As flexible track  15  approaches leading idler wheels  137 , track lugs  32  pass therebetween. In addition, the radially outer surfaces  137   a  of leading idler wheels  137  engage the inner surface  28  of flexible track  15  and direct the lower length of flexible track  15  into contact with a supporting surface such as a farmer&#39;s field. As flexible track  15  continues to be driven about drive wheel  12 , lugs  32  pass between the pairs of leading and trailing bogie wheels  101  and  107 , respectively. As previously described, the radially outer surfaces  101   a  and  107   a  of bogie wheels  101  and  107 , respectively, engage the inner surface  28  of flexible track  15  along its lower length and insure contact of flexible track  15  with the supporting surface along the lower length of flexible track  15 . Similarly, as flexible track  15  approaches trailing idler wheels  117 , track lugs  32  on the inner surface  28  of flexible track  15  pass therebetween. The radially outer surfaces  117   a  of idler wheels  117  engage the inner surface  28  of flexible track  15  and guide flexible track  15  onto drive wheel  12  to form a continuous loop. 
     In the event that flexible track  15  engages an pbstruction on the supporting surface during operation of track apparatus  10 , such obstruction may cause flexible track  15  to deflect thereby causing leading idler axle support  130  to pivot on mounting pin  132  and to urge main piston shaft  139  into main-cylinder chamber  156  of cylinder housing  158  through leading idler wheels  137  and leading idler axle  136 . The amount of force necessary to insert the piston shaft  139  into chamber  156  of cylinder housing  158  (in other words, the amount of force necessary to allow flexible track  15  to deflect) gradually increases as piston shaft  139  is further inserted into chamber  156 , as heretofore described. Once track system  10  clears the obstruction, the piston shaft  139  is urged back into its original position by the nitrogen gas in first portions  196   a  and  206   a  of chambers  196  and  206 , respectively, in corresponding cylinders  184  and  190 , respectively, so as to once again provide the proper tension on flexible track  15 . 
     As described, the structure of track system  10  allows for deflection of the flexible track in response to obstructions or the like while maintaining the proper tension thereon. It can be appreciated that the tension on the flexible track may be adjusted by varying the pressure of the nitrogen gas in first portions  196   a  and  206   a  of chambers  196  and  206 , respectively, in corresponding cylinders  184  and  190 , respectively, and/or by varying the position of limiter member  200 . 
     Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter as regarded as the invention.