Patent Publication Number: US-11661125-B2

Title: Track assembly for traction of an off-road vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/143,784, filed on Sep. 27, 2018; which is a continuation of U.S. patent application Ser. No. 15/348,717, filed Nov. 10, 2016, now U.S. Pat. No. 10,112,663; which is a continuation of U.S. patent application Ser. No. 13/495,823, filed Jun. 13, 2012, now U.S. Pat. No. 9,505,454, which claims priority from U.S. Provisional Patent Application 61/496,114 filed on Jun. 13, 2011, each application is hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to track assemblies for traction of vehicles operable off-road. 
     BACKGROUND 
     Certain off-road vehicles, such as agricultural vehicles (e.g., harvesters, combines, tractors, etc.), construction vehicles (e.g., loaders, bulldozers, excavators, etc.), forestry vehicles (e.g., feller-bunchers, tree chippers, knuckleboom loaders, etc.) and military vehicles (e.g., combat engineering vehicles (CEVs), etc.) to name a few, are used in agricultural fields, construction sites and other areas with a variety of ground surfaces which may be soft, slippery and/or uneven (e.g., soil, mud, sand, ice, snow, etc.) to perform various types of work. 
     Some vehicles ride on tires that propel them on the ground. As they are typically quite heavy and their weight is distributed over a relatively small ground area by their tires, these vehicles apply relatively high pressure on the ground. This high pressure tends to compact the ground on which the vehicles are supported and such ground compaction can be undesirable (e.g., compacted soil can discourage crop growth or otherwise adversely affect the area being compacted). Also, as the tires provide a relatively small contact surface with the ground, traction of these vehicles is often limited, particularly on wet grounds. 
     To address these drawbacks, some vehicles have been provided with track assemblies instead of tire-equipped ground-engaging wheels. These track assemblies typically have elastomeric endless tracks which enhance floatation and traction of the vehicles on the ground. However, existing track assemblies tend to adversely affect other aspects of vehicle performance. For example, existing track assemblies often have no or poor shock or vibration absorption and/or have other characteristics that detrimentally affect ride quality. 
     For these and other reasons, there is a need to improve track systems for traction of off-road vehicles. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the invention, there is provided a track assembly for providing traction to an off-road vehicle. The track assembly has a longitudinal direction, a widthwise direction, and a height direction. The track assembly comprises a frame a plurality of track-contacting wheels, which includes a drive wheel and a plurality of roller wheels. The track assembly also comprises an endless track disposed around the track-contacting wheels. The endless track comprises an inner side facing the track-contacting wheels and a ground-engaging outer side for engaging the ground. The drive wheel engages the endless track to drive the endless track. The roller wheels are disposed to roll on a bottom run of the endless track. The track assembly comprises a bogie carrying at least two of the roller wheels. The track assembly also comprises a resilient device mounted between the frame and the bogie for allowing the bogie to move relative to the frame when the track assembly travels on an uneven ground area. The resilient device comprises a spring. The spring allows movement of the bogie relative to the frame in the height direction of the track assembly and allows movement of the bogie relative to the frame in a direction transversal to the height direction of the track assembly. 
     In accordance with another aspect of the invention, there is provided a track assembly for providing traction to an off-road vehicle. The track assembly comprises a frame a plurality of track-contacting wheels, which includes a drive wheel and a plurality of roller wheels. The track assembly also comprises an endless track disposed around the track-contacting wheels. The endless track comprises an inner side facing the track-contacting wheels and a ground-engaging outer side for engaging the ground. The drive wheel engages the endless track to drive the endless track. The roller wheels are disposed to roll on a bottom run of the endless track. The track assembly comprises a bogie carrying at least two of the roller wheels and pivotable relative to the frame about a pivot axis. The track assembly also comprises a resilient device mounted between the frame and the bogie for allowing the bogie to move relative to the frame when the track assembly travels on an uneven ground area. The resilient device comprises a spring. The spring allows a rotation of the bogie relative to the frame about an axis of rotation transversal to the pivot axis. 
     In accordance with another aspect of the invention, there is provided a track assembly for providing traction to an off-road vehicle. The track assembly comprises a frame a plurality of track-contacting wheels, which includes a drive wheel and a plurality of roller wheels. The track assembly also comprises an endless track disposed around the track-contacting wheels. The endless track comprises an inner side facing the track-contacting wheels and a ground-engaging outer side for engaging the ground. The drive wheel engages the endless track to drive the endless track. The roller wheels are disposed to roll on a bottom run of the endless track. The track assembly comprises a bogie carrying at least two of the roller wheels and pivotable relative to the frame about a pivot axis. The track assembly also comprises a tapered elastomeric spring mounted between the frame and the bogie for allowing the bogie to move relative to the frame when the track assembly travels on an uneven ground area. 
     In accordance with another aspect of the invention, there is provided a track assembly for providing traction to an off-road vehicle. The track assembly comprises a frame a plurality of track-contacting wheels, which includes a drive wheel and a plurality of roller wheels. The track assembly also comprises an endless track disposed around the track-contacting wheels. The endless track comprises an inner side facing the track-contacting wheels and a ground-engaging outer side for engaging the ground. The drive wheel engages the endless track to drive the endless track. The roller wheels are disposed to roll on a bottom run of the endless track. The track assembly comprises a bogie carrying at least two of the roller wheels and pivotable relative to the frame about a pivot axis. The frame enables the roller wheels to be mounted in a plurality of configurations. The plurality of configurations includes a suspension configuration in which the track assembly comprises: a bogie carrying at least two of the roller wheels and pivotable relative to the frame about a pivot axis; and a resilient device mounted between the frame and the bogie for allowing the bogie to move relative to the frame when the track assembly travels on an uneven ground area, the resilient device comprising a spring. The plurality of configurations also includes a suspension-less configuration in which the track assembly: comprises a bogie carrying at least two of the roller wheels and pivotable relative to the frame about a pivot axis; and is free of any spring mounted between the frame and the bogie for allowing the bogie to move relative to the frame when the track assembly travels on an uneven ground area. The plurality of configurations alos includes a bogie-less configuration in which the track assembly is free of any bogie carrying at least two of the roller wheels and pivotable relative to the frame about a pivot axis. 
     In accordance with another aspect of the invention, there is provided a tracked vehicle comprising a plurality of track assemblies. The plurality of track assemblies includes a first track assembly in a front of the tracked vehicle, a second track assembly in the front of the tracked vehicle, a third track assembly in a rear of the tracked vehicle, and a fourth track assembly in the rear of the tracked vehicle. Each track assembly of the plurality of track assemblies comprises: a frame; a plurality of track-contacting wheels which includes a drive wheel and a plurality of roller wheels; and an endless track disposed around the track-contacting wheels, the endless track comprising an inner side facing the track-contacting wheels and a ground-engaging outer side for engaging the ground, the drive wheel engaging the endless track to drive the endless track, the roller wheels being disposed to roll on a bottom run of the endless track. A first one of the track assemblies comprises: a bogie carrying at least two of the roller wheels of the first one of the track assemblies and pivotable relative to the frame of the first one of the track assemblies about a pivot axis; and a resilient device mounted between the frame of the first one of the track assemblies and the bogie of the first one of the track assemblies for allowing the bogie of the first one of the track assemblies to move relative to the frame of the first one of the track assemblies when the first one of the track assemblies travels on an uneven ground area, the resilient device comprising a spring. A second one of the track assemblies is free of any spring mounted between the frame of the second one of the track assemblies and the roller wheels of the second one of the track assemblies. 
     These and other aspects of the invention will now become apparent to those of ordinary skill in the art upon review of the following description of embodiments of the invention in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A detailed description of embodiments of the invention is provided below, by way of example only, with reference to the accompanying drawings, in which: 
         FIG.  1    shows an example of an off-road vehicle comprising track assemblies in accordance with an embodiment of the invention; 
         FIG.  2    shows a track assembly of the vehicle; 
         FIG.  3    shows a frame of the track assembly; 
         FIG.  4    shows a suspension and a bogie of the track assembly; 
         FIGS.  5  and  6    show the frame, the suspension, and the bogie; 
         FIG.  7    shows a variant of the track assembly; 
         FIG.  8    shows a variant of the frame for the track assembly of  FIG.  7   ; 
         FIGS.  9 A and  11    shows a variant of the suspension and the bogie for the track assembly of  FIG.  7   ; 
         FIGS.  9 B to  9 E  illustrates potential movements of the bogie for the track assembly of  FIG.  7     
         FIGS.  10 ,  14  and  15    show the frame, the suspension, and the bogie for the track assembly of  FIG.  7   ; 
         FIGS.  12  and  13    show a resilient device of the suspension of the track assembly of  FIG.  7   ; 
         FIGS.  16  to  19    show another variant of the track assembly in which there is no suspension between the frame and the bogie; 
         FIGS.  20  to  22    show another variant of the track assembly in which there is no bogie pivotable relative to the frame; 
         FIGS.  23  and  24    show a shear spring in a variant of the resilient device of the suspension of the track assembly of  FIG.  7   ; 
         FIGS.  25  to  34    show the frame, the suspension and the bogie of a variant of the track assembly; 
         FIGS.  35  to  38    show a variant of the track assembly of  FIGS.  25  to  34    in which there is no suspension between the frame and the bogie; and 
         FIG.  39    shows the off-road vehicle provided with tire-equipped ground-engaging wheels instead of the track assemblies. 
     
    
    
     It is to be expressly understood that the description and drawings are only for the purpose of illustrating certain embodiments of the invention and are an aid for understanding. They are not intended to be a definition of the limits of the invention. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG.  1    shows an example of an off-road tracked vehicle  10  in accordance with an embodiment of the invention. In this embodiment, the vehicle  10  is a heavy-duty work vehicle for performing agricultural, construction or other industrial work or military work. More particularly, in this embodiment, the vehicle  10  is an agricultural vehicle for performing agricultural work. More specifically, in this example, the agricultural vehicle  10  is a tractor. In other examples, the agricultural vehicle  10  may be a combine harvester, another type of harvester, or any other type of agricultural vehicle. 
     The agricultural vehicle  10  comprises a frame  12  supporting a prime mover  14 , a plurality of track assemblies  16   1 - 16   4  (which can be referred to as “undercarriages”), a working implement  18 , and an operator cabin  20 , which enable an operator to move the agricultural vehicle  10  on the ground to perform agricultural work. 
     The prime mover  14  generates motive power to move the agricultural vehicle  10 . For example, the prime mover  14  may comprise an internal combustion engine and/or one or more other types of motors (e.g., an electric motor) for generating motive power to move the agricultural vehicle  10 . The prime mover  14  is in a driving relationship with each of the track assemblies  16   1 - 16   4 . That is, power derived from the prime mover  14  is transmitted to each of the track assemblies  16   1 - 16   4  via a powertrain of the agricultural vehicle  10  in order to drive the track assemblies  16   1 - 16   4 . 
     The working implement  18  is used to perform agricultural work. For example, in various embodiments, the working implement  18  may include a combine head to cut and/or otherwise process crops, a cutter, a scraper, a tiller or any other type of agricultural working implement. 
     The operator cabin  20  is where the operator sits and controls the agricultural vehicle  10 . More particularly, the operator cabin  20  comprises a set of controls that allow the operator to steer the agricultural vehicle  10  on the ground, operate the working implement  18  and control other aspects of the vehicle  10 . 
     The track assemblies  16   1 - 16   4  engage the ground to propel the agricultural vehicle  10  on the ground. 
     With additional reference to  FIGS.  2  to  6   , in this embodiment, each track assembly  16   i  comprises: a frame  17 ; a plurality of track-contacting wheels, including a driver wheel  24  and a plurality of idler wheels, which includes front (i.e., leading) idler wheels  23   1 ,  23   2 , rear (i.e., trailing) idler wheels  26   1 ,  26   2 , and roller wheels  28   1 - 28   4 ; and an endless track  22  disposed around these wheels. The driver wheel  24  is rotatable by power derived from the prime mover  14  to impart motion to the endless track  22  in order to propel the agricultural vehicle  10  on the ground. The idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   4  do not convert power derived from the prime mover  14  to motive force, but are rather used to do at least one of supporting part of the weight of the agricultural vehicle  10  on the ground via the endless track  22 , guiding the endless track  22  as it is driven by the driver wheel  24 , and tensioning the endless track  22 . As it is driven by the driver wheel  24 , the endless track  22  engages the ground for traction. 
     The track assembly  16   i  has a longitudinal axis  59  (i.e., an axis generally parallel to a longitudinal axis of the agricultural vehicle  10 ) that defines a longitudinal direction of the track assembly  16   i  (i.e., a direction generally parallel to the longitudinal axis  59 ) and transversal directions of the track assembly  16   i  (i.e., directions transverse to the longitudinal axis  59 ), including a widthwise direction of the track assembly  16   i  (i.e., a lateral direction generally perpendicular to the longitudinal axis  59 ). A height direction of the track assembly  16   i  is perpendicular to both the longitudinal direction of the track assembly  16   i  and the widthwise direction of the track assembly  16   i . When the vehicle  10  is on a horizontal ground surface, the height direction of the track assembly  16   i  is thus a vertical direction. The track assembly  16   i  has a length, a width, and a height. 
     The track assembly  16   i  is connected to an axle  32  of the agricultural vehicle  10 . In this case, the axle  32  is a driven axle that is rotated by power derived from the prime mover  14  and delivered via the powertrain of the vehicle  10 . More particularly, in this embodiment, the driver wheel  24  is mounted to the axle  32  of the agricultural vehicle  10 . 
     In some embodiments, the agricultural vehicle  10  may have been designed and manufactured as a tracked vehicle with the track assemblies  16   1 - 16   4  already provided thereon. 
     In other embodiments, as shown in  FIG.  38   , the agricultural vehicle  10  may have been designed and manufactured as a wheeled vehicle propelled on the ground by ground-engaging wheels  15   1 - 15   6  and the track assemblies  16   1 - 16   4  may be used to convert the agricultural vehicle  10  from the wheeled vehicle into a tracked vehicle, thereby enhancing its traction and floatation on the ground. Each ground-engaging wheel  15   1 ,  15   2 ,  15   3 ,  15   4 ,  15   5  or  15   6  is mounted to the axle  32  of the agricultural vehicle  10  and comprises a tire, which may be pneumatic or solid and made of rubber and/or other materials (e.g., agricultural or off-the-road (OTR) tires). In such embodiments, the dimensions of the track assembly  16   i  may allow it to be mounted in place of a ground-engaging wheel  15   1 ,  15   2 ,  15   3 ,  15   4 ,  15   5  or  15   6  by removing the ground-engaging wheel  15   1 ,  15   2 ,  15   3 ,  15   4 ,  15   5  or  15   6  and installing the track assembly  16   i  in its place. 
     The endless track  22  engages the ground to provide traction to the agricultural vehicle  10 . More specifically, the endless track  22  comprises an inner side  25  and a ground-engaging outer side  27 . The inner side  25  faces the wheels  24 ,  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   4  and defines an inner space of the track assembly  16   i  in which these wheels rotate. The ground-engaging outer side  27  engages the ground for traction of the agricultural vehicle  10 . The endless track  22  has a longitudinal axis  45  defining a longitudinal direction of the endless track  22  (i.e., a direction generally parallel to the longitudinal axis  45 ) and transversal directions of the endless track  22  (i.e., directions transverse to the longitudinal axis  45 ), including a widthwise direction of the endless track  22  (i.e., a lateral direction generally perpendicular to the longitudinal axis  45 ). A thickness direction of the endless track  22  is perpendicular to both the longitudinal direction of the track  22  and the widthwise direction of the track  22 . The endless track  22  comprises an upper run  36  which extends from a front longitudinal end  88   1  of the track assembly  16   i  to a rear longitudinal end  88   2  of the track assembly  16   i  and above the drive wheel  24 , and a lower run  19  which extends from the front longitudinal end  88   1  of the track assembly  16   i  to the rear longitudinal end  88   2  of the track assembly  16   i  and under the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   4 . 
     In this embodiment, the endless track  22  is an elastomeric endless track. The track  22  is elastomeric in that it comprises elastomeric material allowing it to elastically change in shape as it is in motion around the wheels  24 ,  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   4 . The elastomeric material of the track  22  can include any polymeric material with suitable elasticity. In this example, the elastomeric material of the track  22  includes rubber. Various rubber compounds may be used and, in some cases, different rubber compounds may be present in different areas of the track  22 . In other examples, the elastomeric material of the track  22  may include another elastomer in addition to or instead of rubber (e.g., polyurethane elastomer). 
     More particularly, in this embodiment, the endless track  22  comprises an elastomeric belt-shaped body  39  underlying its inner side  25  and its ground-engaging outer side  27  and allowing the endless track  22  to elastically change in shape as it is in motion around the wheels  24 ,  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   4 . In view of its underlying nature, the elastomeric belt-shaped body  39  can be referred to as a “carcass”. The carcass  39  comprises elastomeric material. Also, in this embodiment, the carcass  39  comprises one or more reinforcements embedded in its elastomeric material. For example, one such reinforcement may be a layer of reinforcing cables (e.g., cords or wire ropes) that extend generally in the longitudinal direction of the endless track  22  to enhance its strength in tension along its longitudinal direction. Another example of a reinforcement is a layer of reinforcing fabric that comprises pliable material made usually by weaving, felting, or knitting natural or synthetic fibers (e.g., a ply of reinforcing woven fibers). 
     The ground-engaging outer side  27  of the endless track  22  comprises a tread pattern  40  to enhance traction on the ground. The tread pattern  40  comprises a plurality of traction projections  58   1 - 58   T  (sometimes referred to as “traction lugs”, “tread members” or “tread bars”) distributed on the ground-engaging outer side  27 . In this embodiment, each of the traction projections  58   1 - 58   T  has an elongated shape and is angled relative to the longitudinal direction of the endless track  22 . The traction projections  58   1 - 58   T  may have various other shapes in other examples (e.g., curved shapes, shapes with straight parts and curved parts, etc.). In this case, each traction projection  58   i  is an elastomeric traction projection that comprises elastomeric material. 
     The inner side  25  of the endless track  22  comprises a plurality of wheel-contacting projections  34   1 - 34   N  that are positioned to contact at least some of the wheels  24 ,  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   4  to do at least one of driving (i.e., imparting motion to) the track  22  and guiding the track  22 . The wheel-contacting projections  34   1 - 34   N  can be referred to as “wheel-contacting lugs”. Furthermore, since each of them is used to do at least one of driving the track  22  and guiding the track  22 , the wheel-contacting lugs  34   1 - 34   N  can be referred to as “drive/guide projections” or “drive/guide lugs”. 
     In this embodiment, each drive/guide lug  34   i  interacts with the drive wheel  24  to drive the track  22  and interacts with the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   4  to guide the track  22  to maintain proper track alignment and prevent de-tracking. The drive/guide lug  34   i  is thus both a drive lug and a guide lug. In other embodiments, a drive/guide lug  34   i  may interact with the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   4  to guide the track  22  to maintain proper track alignment and prevent de-tracking without being used to drive the track  22 , in which case the drive/guide lug  34   i  is a guide lug. In other embodiments, a drive/guide lug  34   i  may interact with the drive wheel  24  to drive the track  22  without interacting with the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   4 . In this case, each drive/guide lug  34   i  is an elastomeric drive/guide lug that comprises elastomeric material. 
     The drive/guide lugs  34   1 - 34   N  are spaced apart in the longitudinal direction of the endless track  22 . In this case, the drive/guide lugs  34   1 - 34   N  are arranged in a single row. The drive/guide lugs  34   1 - 34   N  may be arranged in other manners in other embodiments (e.g., in a plurality of rows that are spaced apart in the widthwise direction of the track  22 ). 
     The drive wheel  24  is rotatable by power derived from the prime mover  14  to impart motion to the endless track  22 . The drive wheel  24  thus rotates when the axle  32  of the agricultural vehicle  10  rotates. More particularly, in this embodiment, the drive wheel  24  is mounted to the axle  32  of the agricultural vehicle  10 . The drive wheel  24  has an axis of rotation  33  which is defined by the axle  32  of the agricultural vehicle  10 . In this example of implementation, an axis of rotation of the axle  32 , which in this case corresponds to the axis of rotation  33  of the drive wheel  24 , is located between respective axes of rotation  37 ,  35  of the front idler wheels  23   1 ,  23   2  and the rear idler wheels  26   1 ,  26   2  in the longitudinal direction of the track assembly  16   i . The drive wheel  24  contacts the upper run  36  of the endless track  22  and is spaced apart from the lower run  19  of the endless track  22  in the height direction of the track assembly  16   i . 
     More particularly, in this embodiment, the drive wheel  24  is a drive sprocket engaging the drive/guide lugs  34   1 - 34   N  of the endless track  22  in order to drive the track  22 . The drive wheel  24  and the track  22  thus implement a “positive drive” system. The drive wheel  24  comprises a plurality of drive members  78   1 - 78   B  which are circumferentially spaced apart from one another. In this case, the drive members  78   1 - 78   B  extend radially between a hub  79  of the drive wheel  24  and a pair of annular member  80   1 ,  80   2  at a circumference of the drive wheel  24 . The drive wheel  24  and the track  22  have respective dimensions allowing interlocking of the drive members  78   1 - 78   B  of the drive wheel  24  and the drive/guide lugs  34   1 - 34   N  of the track  22 . Adjacent ones of the drive members  78   1 - 78   B  define a space between them to receive one of the drive/guide lugs  34   1 - 34   N . Adjacent ones of the drive/guide lugs  34   1 - 34   N  define a space between them to receive one of the drive members  78   1 - 78   B . 
     The drive wheel  24  may be configured in various other ways in other embodiments. For example, in embodiments where the endless track  22  comprises recesses or holes, the drive wheel  24  may have teeth that enter these recesses or holes in order to drive the track  22 . As another example, in some embodiments, the drive wheel  24  may frictionally engage the inner side  25  of the track  22  in order to frictionally drive the track  22 , i.e., the drive wheel  24  and the track  22  may implement a “friction drive” system. 
     The front idler wheels  23   1 ,  23   2  and the rear idler wheels  26   1 ,  26   2  can support part of the weight of the agricultural vehicle  10  via the endless track  22  and guide the endless track  22  and maintain it under tension as it is driven by the drive wheel  24 . In this embodiment, each of the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2  comprises a wheel body  48  made of rigid material (e.g., steel or other metal) and a peripheral portion  49  made of elastomeric material (e.g., rubber) that enhances its grip on the inner side  25  of the endless track  22 . The front idler wheels  23   1 ,  23   2  are rotatable about an axle and the rear idler wheels  23   1 ,  23   2  are rotatable about an axle. In other embodiments, each of the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2  may be rotatable about a different axle and/or constructed in various other manners and/or using various other materials. 
     The front idler wheels  23   1 ,  23   2  are spaced apart from one another in the widthwise direction of the track assembly  16   i  to define a space therebetween. Similarly, the rear idler wheels  26   1 ,  26   2  are spaced apart from one another in the widthwise direction of the track assembly  16   i  to define a space therebetween. As the endless track  22  is in motion, its drive/guide lugs  34   1 - 34   N  pass in the space between the front idler wheels  23   1 ,  23   2  and in the space between the rear idler wheels  26   1 ,  26   2  and, by being so constrained, help to guide the motion of the endless track  22  to prevent undesired lateral movement or detracking of the track  22 . 
     The roller wheels  28   1 - 28   4  roll on the lower run  19  of the endless track  22  to apply it on the ground for traction and guide the track  22  as it is driven by the drive wheel  24 . Since they are located between the front idler wheels  23   1 ,  23   2  and the rear idler wheels  26   1 ,  26   2  in the longitudinal direction of the track assembly  16   i , the roller wheels  28   1 - 28   4  can be referred to as “mid-rollers”. In this embodiment, each of the mid-rollers  28   1 - 28   4  comprises a wheel body  61  made of rigid material (e.g., steel or other metal) and a peripheral portion  62  made of elastomeric material (e.g., rubber) that enhances its grip on the inner side  25  of the endless track  22 . The mid-rollers  28   1 - 28   4  may be constructed in various other manners and/or using various other materials in other embodiments. 
     In this embodiment, the mid-rollers  28   1 - 28   4  are carried by a bogie  50  of the track assembly  16   i . The bogie  50  is a wheel-carrying assembly that comprises a wheel-carrying structure  63  to which are mounted the mid-rollers  28   1 - 28   4 . The wheel-carrying structure  63  is movable relative to the frame  17 . More particularly, in this embodiment, the wheel-carrying structure  63  is pivotable relative to the frame  17  about a pivot  42  defining a pivot axis  64 . This allows the mid-rollers  28   1 - 28   4  to move up and down as a “tandem” when the wheel-carrying structure  63  pivots about the pivot axis  64  to conform to a ground unevenness, such as a terrain variation (i.e., a terrain elevation or depression such as a hill or bump) and/or an object (e.g., a rock) on the ground. In other words, the pivot axis  64  constitutes a pitch axis for pitching of the bogie  50 . 
     More particularly, in this example of implementation, the wheel-carrying structure  63  comprises an elongated portion  67  extending in the longitudinal direction of the track assembly  16   i  and through which extends the pivot axis  64 . The wheel-carrying structure  63  also comprises wheel mounts  69   1 - 69   4  supporting respective axles of the mid-rollers  28   1 - 28   4 . The wheel-carrying structure  63  may be configured in various other ways in other examples of implementation. 
     In this embodiment, the track assembly  16   i  comprises a tensioning system for maintaining the endless track  22  in tension. In this example, the tensioning system is connected between the frame  17  and the front idler wheels  23   1 ,  23   2  to urge the front idler wheels  23   1 ,  23   2  in a direction to maintain the endless track  22  in tension. More particularly, in this embodiment, the tensioning system is a fluidic tensioning system, i.e., a tensioning system using a fluid such as a hydraulic or pneumatic tensioning system, which comprises a piston-cylinder arrangement connected to a fluid reservoir (e.g., a hydraulic piston-cylinder arrangement connected to a hydraulic accumulator). The piston-cylinder arrangement has a first end portion connected to the frame  17  and a second end portion connected to a link mounted to the axle of the front idler wheels  23   1 ,  23   2 . 
     In addition to its drive wheel  24  being connected to the axle  32  of the agricultural vehicle  10 , in this embodiment, the track assembly  16   i  is connected to a fixed structure of the vehicle  10 . The fixed structure may be the frame  12  of the vehicle  10  or a structure fixed on the frame  12  of the vehicle  10 . More particularly, in this embodiment, the track assembly  16   i  comprises a mounting structure  41  interconnecting the frame  17  of the track assembly  16   i  to a housing of the axle  32  of the vehicle  10  that is fixed to the frame  12  of the vehicle  10 . 
     The track assembly  16   i  comprises a suspension  74  for absorbing shocks, reducing vibrations, and/or improving ride quality. In this embodiment, the suspension  74  comprises a resilient device  75  mounted between the frame  17  and the mid-rollers  28   1 - 28   4 . The resilient device  75  is configured to change from a first configuration to a second configuration in response to a load and recover the first configuration in response to removal of the load to allow movement of the mid-rollers  28   1 - 28   4  relative to the frame  17 . 
     More particularly, in this example of implementation, the resilient device  75  is mounted between the frame  17  and the bogie  50  carrying the mid-rollers  28   1 - 28   4  to allow movement of the bogie  50  relative to the frame  17 . In this example, the resilient device  75  allows movement of the bogie  50  relative to the frame  17  in the height direction of the track assembly  16   i . Thus, when the vehicle  10  is on a horizontal ground surface, the resilient device  75  allows vertical movement of the bogie  50  relative to the frame  17 . 
     The resilient device  75  comprises a spring  80 . The spring  80  is a resilient object that is deformable (i.e., changeable in configuration) such that it changes in configuration under load and recovers its initial configuration when the load is removed. More particularly, in this embodiment, the spring  80  is an elastomeric spring (e.g., a rubber spring). In this example, the elastomeric spring  80  includes an elastomeric body  81  positioned in a housing  82  (e.g., a metallic housing). 
     The elastomeric body  81  includes elastomeric material (e.g., rubber) providing the spring  80  with compliance in the height direction of the track assembly  16   i . A spring rate of the spring  80  is related to the weight of the agricultural vehicle  10  and a load carried by the vehicle  10 . For instance, in some embodiments, the spring  80  may have a spring rate in the height direction of the track assembly  16   i  of at least 4 kN/mm, in some cases at least 6 kN/mm, and in some cases at least 8 kN/mm. The spring rate may have any other suitable value in other embodiments. 
     In this embodiment, the elastomeric body  81  is cylindrical and includes a central opening  70 . The elastomeric body  81  may have various other shapes in other embodiments. 
     The housing  82  houses the elastomeric body  81 . In this embodiment, the housing  82  comprises a top portion  86  and a bottom portion  87  between which the elastomeric body  81  is disposed. In this case, the housing  82  is metallic (e.g., made of steel). In other cases, the housing  82  may be made of other materials. The housing  82  may be configured in various other ways in other embodiments. 
     In some cases, the elastomeric body  81  may rest against the housing  82  without being secured to the housing  82 . In such cases, the bottom portion  87  of the housing  82  keeps the elastomeric body  81  from overextending or falling out when unloaded. In other cases, the elastomeric body  81  may be secured to the housing  82 . For example, in some embodiments, the elastomeric body  81  may be bonded to the housing  82  using a suitable adhesive (e.g., a Chemlok™ rubber-to-metal adhesive in embodiments where the elastomeric body  81  is a rubber body and the housing  82  is metallic). 
     While in this embodiment it is an elastomeric spring, the spring  80  may be any other suitable type of spring in other embodiments. For example, in some embodiments, the spring  80  may be a coil spring (e.g., a metallic or polymeric coil spring), a leaf spring, a fluid spring (i.e., a spring including a liquid or gas contained in a container such as a cylinder or a bellows and variably compressed) such as a gas spring, or any other resilient object that changes in configuration under load and recovers its initial configuration when the load is removed. Thus, deformation (i.e., change in configuration) of the spring  80  may be achieved in various ways in other embodiments. 
     In this embodiment, the suspension  74  comprises a suspension link  85  mounted between the frame  17  and the bogie  50  carrying the mid-rollers  28   1 - 28   4  to control movement of the bogie  50  relative to the frame  17 . More particularly, in this embodiment, the suspension link  85  is secured to the bogie  50  and pivotally connected to the frame  17  about a pivot axis  66  to allow the suspension link  85  to pivot relative to the frame  17  about the pivot axis  66 . In this case, the suspension link  85  is secured to the bogie  50  by fasteners and a pivot pin such that the bogie  50  is pivotable relative to the suspension arm  85  about the pivot axis  64 . The suspension link  85  can help to isolate the spring  80  from all loads except loads in the height direction of the track assembly  16   i  to ensure that the spring  80  deforms in this direction only. 
     The spring  80  rests on top of the suspension link  85 . When the track assembly  16   i  moves on the ground and the mid-rollers  28   1 - 28   4  encounter a bump or other terrain variation, a rock or other object on the ground, or some other ground unevenness, the suspension link  85  can pivot about the pivot axis  66  to allow the bogie  50  to move upwardly against a spring force exerted by the spring  80 , thereby compressing the spring  80 . Upon release of the load to which it is subjected due to the mid-rollers  28   1 - 28   4  having cleared the ground unevenness, the spring  80  can recover its original configuration, biasing the suspension link  85  and the bogie  50  back to their original positions. 
     In this embodiment, the spring  80  is located directly above the bogie  50 . That is, the spring  80  is aligned with the bogie  50  in the longitudinal direction of the track assembly  16   i  (i.e., at least part of the spring  80  overlaps at least part of the bogie  50  in the longitudinal direction of the track assembly  16   i ). More particularly, in this embodiment, the spring  80  is aligned with the pivot axis  64  of the bogie  50  in the longitudinal direction of the track assembly  16   i  (i.e., at least part of the spring  80  overlaps the pivot axis  64  of the bogie  50  in the longitudinal direction of the track assembly  16   i ). 
     The frame  17  is configured to facilitate installation of the suspension  74  in the track assembly  16   i . 
     For example, in this embodiment, the frame  17  comprises a resilient device mounting portion  47  for mounting the resilient device  75 . More particularly, in this example, the resilient device mounting portion  47  includes a cavity  57  for receiving the spring  80 . In some cases, the top portion  86  of the housing  82  of the spring  80  can be secured (e.g., bolted or welded) to an internal surface  55  defining the cavity  57 . In other cases, the top portion  86  of the housing  82  of the spring  80  may be an integral part of the frame  17  (e.g., formed during casting). An opening  56  allows insertion of the spring  80  into the cavity  57  when installing the suspension  74 . In this case, the opening  56  is generally circular. In other cases, the opening  56  may have various other shapes. The resilient device mounting portion  47  may be configured in various other ways in other embodiments. 
     Also, in this embodiment, the frame  17  comprises a suspension link mounting portion  65  for mounting the suspension link  85  to the frame  17  about the pivot axis  66 . More particularly, in this example, the suspension link mounting portion  65  comprises fastening parts  30   1 ,  30   2  to fasten the suspension link  85  to the frame  17  via fasteners (e.g., bolts). In this case, the fastening parts  30   1 ,  30   2  include holes for receiving the fasteners fastening the suspension link  85  to the frame  17 . In addition, in this example, the suspension link mounting portion  65  defines a recess  38  for accommodating a pivotal movement of the suspension link  85  relative to the frame  17  about the pivot axis  66 . The suspension link mounting portion  65  may be configured in various other manners in other embodiments. 
     The suspension  74  may be configured in various other ways and/or using various other materials and/or suspension components in other embodiments. 
     For example, in other embodiments, the suspension  74  may comprise a damper (i.e., a shock absorber), such as a hydraulic or pneumatic damper, a frictional damper (based on dry or fluid friction) or any other type of damper, to dampen shocks experienced by the track assembly  16   i , to a greater extent than the spring  80 . 
     As another example, in other embodiments, the suspension link  85  may be omitted such that the spring  80  is secured directly to the bogie  50 . 
     As another example,  FIGS.  7  to  15    show a variant of the suspension  74  according to another embodiment of the invention. In this embodiment, the suspension  74  comprises a resilient device  175  mounted between the frame  17  and the mid-rollers  28   1 - 28   4 . The resilient device  175  is configured to change from a first configuration to a second configuration in response to a load and recover the first configuration in response to removal of the load to allow movement of the mid-rollers  28   1 - 28   4  relative to the frame  17 . 
     More particularly, in this example of implementation, the resilient device  175  is mounted between the frame  17  and the bogie  50  carrying the mid-rollers  28   1 - 28   4  to allow movement of the bogie  50  relative to the frame  17 . In this example, compliance of the resilient device  175  allows movement of the bogie  50  relative to the frame  17  in the height direction of the track assembly  16   i . An example of such a movement is represented by arrow M h  in  FIG.  9 B , where the arrow M h  represents a velocity vector of a point of the bogie  50  at an instant at which the movement of the bogie  50  relative to the frame  17  begins. Thus, when the vehicle  10  is on a horizontal ground surface, the resilient device  175  allows vertical movement of the bogie  50  relative to the frame  17 . 
     In addition, in this example of implementation, compliance of the resilient device  175  allows the bogie  50  to move relative to the frame  17  transversally to the height direction of the track assembly  16   i , i.e., allows movement of the bogie  50  relative to the frame  17  in a direction transversal to the height direction of the track assembly  16   i . An example of such a movement is represented by arrow M t  in  FIG.  9 C , where the arrow M t  represents a velocity vector of a point of the bogie  50  at an instant at which the movement of the bogie  50  relative to the frame  17  begins. As such, when the vehicle  10  is on a horizontal ground surface, the resilient device  175  allows movement of the track assembly  16   i  in a non-vertical direction (i.e., a direction not purely vertical). 
     A movement of the bogie  50  relative to the frame  17  in a direction transversal to the height direction of the track assembly  16   i  induces a displacement of the bogie  50  relative to the frame  17  that can be viewed as including at least one of: (i) a translation of the bogie  50  relative to the frame  17  in the longitudinal direction of the track assembly  16   i , as represented by arrow T l  in  FIG.  9 C ; (ii) a translation of the bogie  50  relative to the frame  17  in the widthwise direction of the track assembly  16   i , as represented by arrow T w  in  FIG.  9 C ; (iii) a rotation of the bogie  50  relative to the frame  17  about an axis of rotation R l  generally parallel to the longitudinal direction of the track assembly  16   i  (i.e., generally parallel to the longitudinal axis  59  of the track assembly  16   i ); and (iv) a rotation of the bogie  50  relative to the frame  17  about an axis of rotation R w  generally parallel to the widthwise direction of the track assembly  16   i  (i.e., generally perpendicular to the longitudinal axis  59  of the track assembly  16   i ). The displacement of the bogie  50  resulting from the movement of the bogie  50  relative to the frame  17  transversal to the height direction of the track assembly  16   i  may also include at least one of: (i) a translation of the bogie relative to the frame  17  in the height direction of the track assembly  16   i , as represented by arrow T h  in  FIG.  9 C ; and (ii) a rotation of the bogie  50  relative to the frame  17  about an axis of rotation R h  generally parallel to the height direction of the track assembly  16   i . 
     This ability of the bogie  50  to move relative to the frame  17  transversally to the height direction of the track assembly  16   i  thus provides additional degrees of freedom of movement of the bogie  50 . For example, in this embodiment, the ability of the bogie  50  to translate relative to the frame  17  in the widthwise direction of the track assembly  16   i  (arrow T w ) and rotate relative to the frame  17  about the axis of rotation R l  generally parallel to the longitudinal direction of the track assembly  16   i  provides a “roll” capability to the bogie  50 . In that sense, the axis of rotation R l  of the bogie  50  can be viewed as a “roll” axis. Furthermore, the ability of the bogie  50  to translate relative to the frame  17  in the longitudinal direction of the track assembly  16   i  (arrow T l ) and rotate relative to the frame  17  about the axis of rotation R w  generally parallel to the widthwise direction of the track assembly  16   i  provides an additional “pitch” capability to the bogie  50 , which is additional to pitching of the bogie  50  about its pitch axis  64 . In that sense, the axis of rotation R w  of the bogie  50  can be viewed as an additional “pitch” axis. 
     Since in this embodiment the pivot axis  64  of the bogie  50  is transversal (in this case perpendicular) to the longitudinal direction of the track assembly  16   i , the axis of rotation R l  generally parallel to the longitudinal direction of the track assembly  16   i  about which the bogie  50  can rotate due to compliance of the resilient device  175  is also transversal (in this case perpendicular) to the pivot axis  64  of the bogie  50 . 
     The resilient device  175  comprises a spring  180 . The spring  180  is a resilient object that is deformable such that it changes in configuration under load and recovers its initial configuration when the load is removed. More particularly, in this embodiment, the spring  180  is an elastomeric spring (e.g., a rubber spring). In this example, the elastomeric spring  180  includes an elastomeric body  181  positioned in a housing  182  (e.g., a metallic housing). 
     The elastomeric body  181  includes elastomeric material (e.g., rubber) providing the spring  180  with compliance in the height direction of the track assembly  16   i . A spring rate of the spring  180  is related to the weight of the agricultural vehicle  10  and a load carried by the vehicle  10 . For instance, in some embodiments, the spring  180  may have a spring rate in the height direction of the track assembly  16   i  of at least 4 kN/mm, in some cases at least 6 kN/mm, and in some cases at least 8 kN/mm. The spring rate may have any other suitable value in other embodiments. 
     In this embodiment, the spring  180  is tapered such that the elastomeric body  181  is tapered. Specifically, in this case, the spring  180  is conical such that the elastomeric body  181  is conical. The elastomeric body  181  includes a central opening  170 . The elastomeric body  181  may have various other shapes in other embodiments. 
     The tapered (in this case conical) shape of the spring  180  provides the spring  180  with compliance in directions transversal to the height direction of the track assembly  16   i  (i.e., in non-vertical directions when the vehicle  10  is on a horizontal ground surface). For example, in some embodiments, the spring  180  may have a spring rate in a direction transversal to the height direction of the track assembly  16   i  that is no less than (i.e., equal to or greater than) its spring rate in the height direction of the track assembly  16   i . For instance, in this embodiment, the spring  180  may have a spring rate in each of the longitudinal direction of the track assembly  16   i  and the widthwise direction of the track assembly  16   i  that is no less than its spring rate in the height direction of the track assembly  16   i . In this case, the conical configuration of the spring  180  can provide substantially equal stiffness in all directions perpendicular to the height direction of the track assembly  16   i . Thus, when the vehicle  10  is on a horizontal ground surface, the spring  180  may have a spring rate in a non-vertical direction (e.g., a horizontal direction) that is no less than its spring rate in the vertical direction. In this case, the conical configuration of the spring  180  can provide substantially equal stiffness in all horizontal directions. 
     While in this embodiment it is conical, in other embodiments, the spring  180  may be configured differently but still provide compliance in one or more directions transversal to the height direction of the track assembly  16   i . For example, in some embodiments, as shown in  FIGS.  23  and  24   , the spring  180  may comprise a plurality of (in this case two) shear spring pads  198   1 ,  198   2 . In this case, the shear spring pads  198   1 ,  198   2  are rectangular rubber pads arranged opposite to one another in a converging relationship at an angle to the height direction of the track assembly  16   i . Shear spring pads such as the shear spring pads  198   1 ,  198   2  may have various other shapes, may be arranged in various other manners, and/or may be present in various other numbers in other cases (e.g., compound angle shear pads). Examples of shear springs that may be used in some embodiments include Chevron™ springs and Offset Shear™ springs commercialized by Trelleborg Industrial AVS and equivalent shear springs. 
     The housing  182  houses the elastomeric body  181 . In this embodiment, the housing  182  is tapered, in this case conical. The housing  182  comprises an outer portion  186  and an inner portion  187  between which the elastomeric body  181  is disposed. The outer portion  186  is secured to the frame  17 . More particularly, in this example, the outer portion  186  includes a flange  169  comprising holes  143   1 - 143   3  for receiving fasteners to fasten the housing  182  to the frame  17 . To that end, in this embodiment, the frame  17  comprises holes  91   1 - 91   4  for receiving the fasteners extending through the holes  143   1 - 143   3  of the housing  182 . In this case, the housing  182  is metallic (e.g., made of steel). In other cases, the housing  182  may be made of other materials. The housing  182  may be configured in various other ways in other embodiments. 
     The elastomeric body  181  may be secured to the housing  182 . For example, in some embodiments, the elastomeric body  181  may be bonded to the housing  182  using a suitable adhesive (e.g., a Chemlok™ rubber-to-metal adhesive in embodiments where the elastomeric body  181  is a rubber body and the housing  82  is metallic). 
     In this embodiment, the resilient device  175  supports the mid-rollers  28   1 - 28   4 . More particularly, in this embodiment, the resilient device  175  supports the bogie  50  carrying the mid-rollers  28   1 - 28   4 . To that end, the resilient device  175  comprises a support  190  coupled to the bogie  50  to support the bogie  50 . In this example, the support  190  extends from the inner portion  187  of the housing  182  and includes a pair of brackets  192   1 ,  192   2  which are spaced apart in the widthwise direction of the track assembly  16   i  and configured to receive a central part of the bogie  50  through which passes the bogie&#39;s pivot axis  64 . In this case, the support  190  is integral with the inner portion  187  of the housing  182 . Each of the brackets  192   1 ,  192   2  includes an opening  193  to receive a portion of the bogie  50  and a plurality of holes  194   1 - 194   4  to receive fasteners fastening the bogie  50  to the support  190 . The support  190  may be configured in various other ways in other embodiments. 
     In this example of implementation, the spring  180  is located directly above the bogie  50 . That is, the spring  180  is aligned with the bogie  50  in the longitudinal direction of the track assembly  16   i  (i.e., at least part of the spring  180  overlaps at least part of the bogie  50  in the longitudinal direction of the track assembly  16   i ). 
     More particularly, in this embodiment, the spring  180  is aligned with the pivot axis  64  of the bogie  50  in the longitudinal direction of the track assembly  16   i  (i.e., at least part of the spring  180  overlaps the pivot axis  64  of the bogie  50  in the longitudinal direction of the track assembly  16   i ). 
     When a ground area beneath the mid-rollers  28   1 - 28   4  is uneven (e.g., due to a terrain elevation or a rock or other object on the ground beneath the mid-rollers  28   1 - 28   4 ), the suspension  74  allows the bogie  50  to move upwardly relative to the frame  17  against a spring force exerted by the spring  180 , thereby deforming the spring  180 . Upon release of the load to which it is subjected due to the mid-rollers  28   1 - 28   4  having cleared the uneven ground area, the spring  180  can recover its original configuration, biasing the bogie  50  back to its original position. 
     The bogie  50  may move relative to the frame  17  in the height direction of the track assembly  16   i , as shown by arrow M h  in  FIG.  9 B . In this example, this movement induces a translation of the bogie  50  relative to the frame  17  and shearing of the spring  180  in the height direction of the track assembly  16   i . 
     In some cases, the bogie  50  may move relative to the frame  17  in a direction transversal to the height direction of the track assembly  16   i , as shown by arrow M t  in  FIG.  9 C . In this example, this movement induces at least one of: (i) a translation of the bogie  50  relative to the frame  17  in the longitudinal direction of the track assembly  16   i , as represented by arrow T l ; (ii) a translation of the bogie  50  relative to the frame  17  in the widthwise direction of the track assembly  16   i , as represented by arrow T w ; (iii) a rotation of the bogie  50  relative to the frame  17  about an axis of rotation R l  generally parallel to the longitudinal direction of the track assembly  16   i ; and (iv) a rotation of the bogie  50  relative to the frame  17  about an axis of rotation R w  generally parallel to the widthwise direction of the track assembly  16   i . This movement may also include a translation of the bogie relative to the frame  17  in the height direction of the track assembly  16   i , as represented by arrow T h , and/or a rotation of the bogie  50  relative to the frame  17  about an axis of rotation R h  generally parallel to the height direction of the track assembly  16   i . In such cases, this movement causes compression of a portion of the elastomeric body  181 , stretching of an opposite portion of the elastomeric body  182 , and possibly shearing of the elastomeric body  182 . 
     For example, in this embodiment, as shown in  FIG.  9 D , when a ground area beneath the mid-rollers  28   1 - 28   4  is uneven in the widthwise direction of the track assembly  16   i  (e.g., due to a side hill or other terrain variation, a rock or other object on the ground beneath the mid-rollers  28   1 ,  28   2  or beneath the mid-rollers  28   1 ,  28   3 , etc.), the compliance of the spring  180  in the height direction of the track assembly  16   i  and in the widthwise direction of the track assembly  16   i  allows movement of the bogie  50  relative to the frame  17  in a direction transversal to the height direction of the track assembly  16   i  (arrow M t ) such that the bogie  50  is displaced relative to the frame  17  both in the height direction of the track assembly  16   i  and in the widthwise direction of the track assembly  16   i  in order to conform to the uneven ground area. In this case, this movement of the bogie  50  relative to the frame  17  can be viewed as inducing a translation T w  of the bogie  50  relative to the frame  17  in the widthwise direction of the track assembly  16   i  and a rotation of the bogie  50  about an axis of rotation R l  generally parallel to the longitudinal direction of the track assembly  16   i . This rotation of the bogie  50  can be seen as a quasi-pivotal movement of the bogie  50  about the axis of rotation R l . In some cases, the rotation of the bogie  50  about the axis of rotation R l  may be more significant than the translation T w  of the bogie  50  relative to the frame  17  in the widthwise direction of the track assembly  16   i . In other cases, the translation T w  of the bogie  50  relative to the frame  17  in the widthwise direction of the track assembly  16   i  may be more significant than the rotation of the bogie  50  about the axis of rotation R l . 
     A rotation of the bogie  50  about an axis of rotation R l  generally parallel to the longitudinal direction of the track assembly  16   i  allowed by the spring  180  defines an angular displacement θ l  of the bogie  50  relative to the frame  17 . The angular displacement θ l  of the bogie  50  can take on any suitable value. For example, in some embodiments, the angular displacement θ l  of the bogie  50  may be at least 1°, in some cases at least 2°, in some cases at least 3°, and in some cases even more (e.g., 5°, 10°, 15° or more). The angular displacement θ l  of the bogie  50  can take on various other values in other embodiments. 
     In some cases, as represented in  FIG.  9 E , movement of the bogie  50  relative to the frame  17  due to deformation of the spring  180  may induce a rotation of the bogie  50  about an axis of rotation R w  generally parallel to the widthwise direction of the track assembly  16   i , which can be seen as a quasi-pivotal movement of the bogie  50  about the axis of rotation R w  generally parallel to the widthwise direction of the track assembly  16   i . This rotation of the bogie  50  about the axis of rotation R w  generally parallel to the widthwise direction of the track assembly  16   i  allowed by the spring  180  defines an angular displacement θ w  of the bogie  50  relative to the frame  17 . The angular displacement θ w  of the bogie  50  can take on any suitable value. For example, in some embodiments, the angular displacement θ w  of the bogie  50  may be at least 1°, in some cases at least 2°, in some cases at least 3°, and in some cases even more (e.g., 5°, 10°, 15° or more). The angular displacement θ w  of the bogie  50  can take on various other values in other embodiments. 
     The rotation of the bogie  50  about an axis of rotation R w  generally parallel to the widthwise direction of the track assembly  16   i  allowed by the spring  180  and the angular displacement θ w  of the bogie  50  relative to the frame  17  that it defines may occur in addition to a rotation of the bogie  50  about its pivot axis  64 . The rotation of the bogie  50  about its pivot axis  64  defines an angular displacement θ p  of the bogie  50  relative to the frame  17 . The angular displacement θ p  of the bogie  50  can take on any suitable value. For example, in some embodiments, the angular displacement θ p  of the bogie  50  may be at least 4°, in some cases at least 6°, in some cases at least 8°, in some cases at least 10°, and in some cases even more (e.g., 15° or more). Thus, in such embodiments, a total angular displacement θ w-tot  of the bogie  50  relative to the frame  17  about axes parallel to the widthwise direction of the track assembly  16   i  corresponds to a sum of the angular displacement θ p  of the bogie  50  due to pivoting of the wheel-carrying structure  63  about the pivot axis  64  and the angular displacement θ w  of the bogie  50  due to compliance of the spring  180 . 
       FIGS.  25  to  34    show a variant of the track assembly  16   i  according to another embodiment of the invention. In this embodiment, the track assembly  16   i  comprises a movement limiter  183  for limiting movement of the bogie  50  relative to the frame  17 . More particularly, in this embodiment, the movement limiter  183  is a spring deformation limiter for limiting deformation of the spring  180  of the suspension  74  to limit movement of the bogie  15  due to deformation of the spring  180 . This prevents the spring  180  from being over stretched or over compressed during use. 
     In this example of implementation, the spring deformation limiter  183  acts to limit the various degrees of freedom of movement of the bogie  50  relative to the frame  17 , including a rotation of the bogie  50  relative to the frame  17  about an axis of rotation R l  generally parallel to the longitudinal direction of the track assembly  16   i  and a rotation of the bogie  50  relative to the frame  17  about an axis of rotation R w  generally parallel to the widthwise direction of the track assembly  16   i . 
     In this embodiment, the spring deformation limiter  183  comprises a plurality of movement stoppers  189   1 - 189   3 . In this example, each of the stoppers  189   1 - 189   3  comprises a first stopping part, namely an abutment member  191   1 ,  191   2 ,  191   3 , which can abut on a second stopping part, namely a part of the inner portion  187  of the housing  182  of the spring  180 , to stop movement of the inner portion  187  of the housing  182 . More particularly, in this example, the abutment member  191   1 ,  191   2 ,  191   3 , of each of the stoppers  189   1 - 189   3  is an abutment projection that extends into an opening  195  of that stopper defined by the inner portion  187  of the housing  182 . In this case, the abutment member  191   1 ,  191   2  of each of the movement stoppers  189   1 - 189   2 is part of the outer portion  186  of the housing  182 , while the abutment member  191   3  of the movement stopper  189   3  is part of the frame  17 . The movement stoppers  189   1 - 189   3  may be configured in any other suitable way in other embodiments. 
     The spring deformation limiter  183  may be implemented in various other manners in other embodiments. For example, the spring deformation limiter  183  may comprise any number of movement stoppers such as the movement stoppers  189   1 - 189   3  in other embodiments (i.e., a single movement stopper, two movement stoppers, or more than three movement stoppers). 
     In this embodiment, the frame  17  comprises a forklift receiver  97  for receiving a forklift to lift the track assembly  16   i  when it is to be transported to or from the vehicle  10  for installation or removal therefrom. More particularly, in this embodiment, the forklift receiver  97  comprises a pair of forklift-receiving openings  96   1 ,  96   2  for receiving a pair of fork members of the forklift. 
     In some embodiments, the track assembly  16   i  may enable different mounting configurations for the mid-rollers  28   1 - 28   4  using the same frame  17 . For example, in various embodiments, the frame  17  may allow the mid-rollers  28   1 - 28   4  to be mounted: (i) with the suspension  74 , i.e., a “suspension” configuration, as discussed above; (ii) without the suspension  74 , i.e., a “suspension-less” or “no-suspension” configuration; or without a pivotable bogie such as the bogie  50 , i.e., a “bogie-less” or “hardbottom” configuration. 
     As an example, in some embodiments, as shown in  FIGS.  16  to  19   , the track assembly  16   i  discussed above in respect of  FIGS.  7  to  15    may be used without the suspension  74  such that there is no resilient device between the bogie  50  carrying the mid-rollers  28   1 - 28   4  and the frame  17  (i.e., a “no-suspension” configuration). In this embodiment, the track assembly  16   i  comprises a support  290  coupled to the frame  17  and to the bogie  50  to support the bogie  50 . In this case, the support  290  is configured similarly to the support  190  of the resilient device  175  discussed above. 
     More particularly, in this case, the support  290  includes a pair of brackets  292   1 ,  292   2  which are spaced apart in the widthwise direction of the track assembly  16   i  and configured to receive a central part of the bogie  50  through which passes the bogie&#39;s pivot axis  64 . Each of the brackets  292   1 ,  292   2  includes an opening  293  to receive a portion of the bogie  50  and a plurality of holes  294   1 - 294   4  to receive fasteners fastening the bogie  50  to the support  290 . Also, in this example, the support  290  comprises a flange  269  including holes  243   1 - 243   2  for receiving fasteners to fasten the support  290  to the frame  17  via the frame&#39;s holes  91   1 - 91   4 . The support  290  may be configured in various other ways in other embodiments. 
       FIGS.  35  to  38    show a variant of the track assembly  16   i  without the suspension  74  such that there is no resilient device between the bogie  50  carrying the mid-rollers  28   1 - 28   4  and the frame  17  (i.e., a “no-suspension” configuration), in accordance with another embodiment of the invention. In this embodiment, the track assembly  16   i  comprises a movement limiter  283  for limiting movement of the bogie  50  relative to the frame  17 . More particularly, in this embodiment, the movement limiter  283  is a pivot limiter for limiting pivoting of the bogie  50  about its pivot axis  64 . 
     In this embodiment, the pivot limiter  283  comprises a plurality of movement stoppers  289   1 ,  289   2 . In this example, each of the stoppers  289   1 ,  289   2  comprises a pair of stopping parts, namely abutment member  291   1 ,  291   2 , which can abut one another to stop pivoting of the bogie  50  about its pivot axis  64 . More particularly, in this example, each of the abutment members  291   1 ,  291   2  of each of the stoppers  289   1 ,  289   2  is an abutment projection. In this case, the abutment member  291   1  of each of the movement stoppers  289   1 ,  289   2  is part of the bogie  50 , while the abutment member  291   2  of each of the movement stoppers  289   1 ,  289   2  is part of the frame  17  (as can also be seen in  FIG.  30   ). The movement stoppers  289   1 ,  289   2  may be configured in any other suitable way in other embodiments. 
     The pivot limiter  283  may be implemented in various other manners in other embodiments. For example, the pivot limiter  283  may comprise any number of movement stoppers such as the movement stoppers  289   1 ,  289   2  in other embodiments (i.e., a single movement stopper, or more than two movement stoppers). 
     As another example, in some embodiments, as shown in  FIGS.  20  to  22   , the track assembly  16   i  discussed above in respect of  FIGS.  7  to  15    may be used without a pivotable bogie carrying the mid-rollers  28   1 - 28   4  such as the bogie  50  such that the mid-rollers  28   1 - 28   4  are rigidly mounted to the frame  17  (i.e., a “hardbottom” configuration). In this embodiment, a wheel-carrying structure  363  carrying the mid-rollers  28   1 - 28   4  is rigidly secured to the frame  17 . 
     More particularly, in this embodiment, the wheel-carrying structure  363  comprises an elongated portion  367  extending in the longitudinal direction of the track assembly  16   i  and wheel mounts  369   1 - 369   4  supporting respective axles of the mid-rollers  28   1 - 28   4 . The wheel-carrying structure  363  also comprises a flange  369  including holes  343   1 - 343   4  for receiving fasteners to fasten the wheel-carrying structure  363  to the frame  17  via the frame&#39;s holes  91   1 - 91   4 . The wheel-carrying structure  363  may be configured in various other ways in other examples of implementation 
     The flexibility in how the mid-rollers  28   1 - 28   4  are mountable to the frame  17  may be useful to better fit the track assembly  16   i  to the needs of a manufacturer or user of the agricultural vehicle  10  and/or to the application in which the vehicle  10  is used. 
     For example, in some embodiments, on a four-track vehicle such as the agricultural vehicle  10  considered above, the mid-rollers  28   1 - 28   4  of the track assembly  16   1  in a front of the vehicle  10  may be mounted to the frame  17  of the track assembly  16   1  in a manner different from that in which the mid-rollers  28   1 - 28   4  of the track assembly  16   3  in a rear of the vehicle  10  are mounted to the frame  17  of the track assembly  16   3 , yet the frame  17  of these two track assemblies may be substantially identical. For instance, in some cases, the track assembly  16   1  in the front of the vehicle  10  may have the “suspension” configuration (i.e., include the suspension  74 ) as discussed in respect of  FIGS.  7  to  15   , while the track assembly  16   3  in the rear of the vehicle  10  may have the “no-suspension” configuration (i.e., not include the suspension  74 ) as discussed in respect of  FIGS.  16  to  19    or the “hardbottom” configuration (i.e., not include the pivotable bogie  50 ) as discussed in respect of  FIGS.  20  to  22   . For example, such an arrangement may be employed if, because of the position of the operator cabin  20  and the operator&#39;s seat on the agricultural vehicle  10 , a majority of the ride quality benefit may be achieved by using the “suspension” configuration only in the front track assemblies  16   1 - 16   2  that are connected to the front axle  32  of the vehicle  10 . Also, in some cases, the front or rear axle  32  of the vehicle  10  may have an axle suspension and this can determine where the “suspension” configuration for the track assembly  16   i  would be used. Various other combinations of the “suspension” configuration, “no-suspension” configuration, and the “hardbottom” configuration may be used in other cases. 
     As another example, in some embodiments, use of the “suspension” configuration, the “no-suspension” configuration, or the “hardbottom” configuration in a track assembly  16   i  may be based on a preference of the manufacturer or user of the agricultural vehicle  10 . For instance, the track assembly  16   i  may be standardly offered with the “no-suspension” configuration or the “hardbottom” configuration, but optionally upgradable to the “suspension” configuration by adding the suspension  74 . 
     While in this embodiment the track assemblies  16   1 - 16   4  are configured in a certain way, the track assemblies  16   1 - 16   4  may be configured in various other ways in other embodiments. 
     For example, in other embodiments, the track assembly  16   i  may comprise more or less mid-rollers such as the mid-rollers  28   1 - 28   4 . For instance, in some cases, the track assembly  16   i  may comprise additional mid-rollers, possibly arranged in one or more additional tandems. In other cases, the track assembly  16   i  may not comprise any tandem. 
     As another example, the endless track  22  may be constructed in various other ways and/or using various other materials in other embodiments. Also, while in this embodiment the endless track  22  is a one-piece jointless track, in other embodiments, the endless track  22  may be a “segmented” track comprising a plurality of track sections interconnected to one another at a plurality of joints. In other embodiments, the endless track  22  may be a one-piece track that can be closed like a belt with connectors at both of its longitudinal ends to form a joint. 
     As yet another example, in other embodiments, instead of having the drive wheel  24  mounted to the axle  32  of the agricultural vehicle  10 , the track assembly  16   i  may comprise a transmission between the axle  32  of the agricultural vehicle  10  and the drive wheel  24  to transmit power from the axle  32  to the drive wheel  24  and perform a speed conversion such that the drive wheel  24  rotates at a rotational speed different from a rotational speed of the axle  32 . 
     Although in embodiments considered above the track assemblies  16   1 - 16   4  are provided both in the front and the rear of the agricultural vehicle  10 , in other embodiments, the track assemblies  16   1 ,  16   2  or the track assemblies  16   3 ,  16   3  may be replaced by ground-engaging wheels such as the ground-engaging wheels  15   1 - 15   8  discussed above in respect of  FIG.  23   . For instance, in some embodiments, the agricultural vehicle  10  may be propelled by the track assemblies  16   1 ,  16   2  in the front and by ground-engaging wheels such as the ground-engaging wheels  15   1 - 15   8  in the rear. 
     While in embodiments considered above the agricultural vehicle  10  has two track assemblies on each of its lateral sides, in other embodiments, the vehicle  10  may have a single track assembly on each lateral side. In such embodiments, this track assembly may be elongated in the longitudinal direction of the vehicle  10  such that it extends from the front to the rear of the vehicle  10  and may have a drive wheel located at longitudinal end of the track assembly (as opposed to between the front idler wheels  23   1 ,  23   2  and the rear idler wheels  26   1 ,  26  in the track assembly  16   i  discussed above) and an idler wheel at an opposite longitudinal end of the track assembly. 
     Although in embodiments considered above the off-road vehicle  10  is an agricultural vehicle for performing agricultural work, in other embodiments, the vehicle  10  may be a construction vehicle (e.g., a loader, a bulldozer, an excavator, etc.) for performing construction work, a forestry vehicle (e.g., a feller-buncher, a tree chipper, a knuckleboom loader, etc.) for performing forestry work, a military vehicle (e.g., a combat engineering vehicle (CEV), etc.) for performing work in a military application, a transporter vehicle (e.g., a heavy hauler, a flatbed truck, a trailer, a carrier, etc.) for transporting equipment, materials, cargo or other objects, or any other vehicle operable off paved roads. Although operable off paved roads, the vehicle  10  may also be operable on paved roads in some cases. Also, while in embodiments considered above the vehicle  10  is driven by a human operator in the vehicle  10 , in other embodiments, the vehicle  10  may be an unmanned ground vehicle (e.g., a teleoperated or autonomous unmanned ground vehicle). 
     Any feature of any embodiment discussed herein may be combined with any feature of any other embodiment discussed herein in some examples of implementation. 
     While various embodiments and examples have been presented, this was for the purpose of describing, but not limiting, the invention. Various modifications and enhancements will become apparent to those of ordinary skill in the art and are within the scope of the invention, which is defined by the appended claims.