Patent Publication Number: US-2015068823-A1

Title: Undercarriage for a power machine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims the benefit of U.S. provisional patent application Ser. No. 61/875,885, filed Sep. 10, 2013, the content of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     This disclosure is directed toward power machines. More particularly, this disclosure is related to the undercarriage for power machines that employ endless tracks as tractive elements. Power machines, for the purposes of this disclosure, include any type of machine that generates power for the purpose of accomplishing a particular task or a variety of tasks. One type of power machine is a work vehicle. Work vehicles are generally self-propelled vehicles that have a work device, such as a lift arm (although some work vehicles can have other work devices) that can be manipulated to perform a work function. Work vehicles include loaders, excavators, utility vehicles, tractors, and trenchers, to name a few examples. 
     Tractive elements are devices that engage a support surface such as the ground to cause the power machine to move over the support surface. Many power machines employ wheels as tractive elements, but other power machines employ endless tracks, skids, or any combination of tractive elements. Some undercarriages that include endless tracks include track frames with various components mounted to them for the purpose of engaging the endless track and provide proper tensioning of the endless track. These components typically include idlers, rollers, or some combination of idlers and rollers. 
     Power machines that employ one or more endless tracks as tractive elements utilize various components such as rollers and idlers to maintain proper tension on the endless tracks as they move over a support surface, such as the ground. Such rollers and idlers are coupled to a track frame via various members, which in some instances provide for a variable suspension mounting, as opposed to a rigid mounting. One such suspension mounting for rollers on a power machine is described in U.S. Pat. No. 7,552,785. 
     The suspension mounting for rollers described in U.S. Pat. No. 7,552,785 includes a plurality of leaf springs stacked together to provide increasing spring force as the wheels or track rollers are deflected. Each stack of springs is coupled to a track roller and is held together by a block on the opposing end of the springs relative to the track roller. The block on each of the spring stacks or assemblies serves as a stop block for the spring assembly positioned forward of it. This stop block was designed to interfere with the wheel end of the spring assembly to limit upward travel of the spring. 
     The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. 
     SUMMARY 
     This summary and the abstract are provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. The summary and the abstract are not intended to identify key features or essential features of the claimed subject matter, nor are they intended to be used as an aid in determining the scope of the claimed subject matter. 
     Disclosed embodiments include undercarriages and components for use in undercarriages for power machines. A disclosed undercarriage, in one embodiment, includes roller mounting structures for mounting rollers to a track frame. The roller mounting structures include one or more of disclosed mono-leaf springs to provide a suspension mounting of the rollers. In another embodiment, the disclosed undercarriage has an adjustable idler mounting structure for coupling an idler to the track frame having various advantageous features. In yet another embodiment, an improved idler is disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side perspective view of a power machine upon which various embodiments of the present disclosure are capable of being employed. 
         FIG. 2  is a block diagram illustrating components of an undercarriage for a power machine such as the power machine illustrated in  FIG. 1 . 
         FIG. 3  is a block diagram of a track frame assembly that is employable with the undercarriage of  FIG. 2 . 
         FIG. 4  is a diagrammatic perspective view of an undercarriage of a track vehicle illustrating portions of a track frame assembly according to one illustrative embodiment. 
         FIG. 5  is a perspective view illustrating one embodiment of a roller assembly configured for use with the undercarriage of  FIG. 4 . 
         FIG. 6  is a side view of one embodiment of a roller mounting structure suited for use with the roller assembly illustrated in  FIG. 5 . 
         FIG. 7  illustrates an idler mounting structure mounted in the undercarriage of  FIG. 4  according to one illustrative embodiment. 
         FIG. 8  illustrates the idler mounting structure of  FIG. 7  with a cutaway perspective to show internal components. 
         FIG. 9  is an illustration of an undercarriage according to another illustrative embodiment. 
         FIG. 10  is illustrates a portion of the undercarriage of  FIG. 9 . 
         FIG. 11  illustrates an idler pulley according to one illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The concepts disclosed in this discussion are described and illustrated with reference to exemplary embodiments. These concepts, however, are not limited in their application to the details of construction and the arrangement of components in the illustrative embodiments and are capable of being practiced or being carried out in various other ways. The terminology in this document is used for the purpose of description and should not be regarded as limiting. Words such as “including,” “comprising,” and “having” and variations thereof as used herein are meant to encompass the items listed thereafter, equivalents thereof, as well as additional items. 
     The embodiments discussed below provide illustrative examples of undercarriages for various power machines. In particular, the embodiments illustrate track assemblies and components for track assemblies for undercarriages that include one or more endless tracks as tractive elements. A representative power machine on which the embodiments can be practiced is illustrated in  FIG. 1  and described below before any embodiments are disclosed. For the sake of brevity, only one representative power machine is discussed. However, as mentioned above, the embodiments below can be practiced on any of a number of power machines, including power machines of different types from the representative power machine discussed below. Power machines, for the purposes of this discussion, include a frame, at least one work element, and a power source that is capable of providing power to the work element to accomplish a work task. Work vehicles are power machines where at least one of the work elements is a motive system for moving the power machine under power. The disclosed embodiments can be practiced on a power machine such as shown in  FIG. 1  or various other power machines that include endless tracks as tractive elements, whether or not the power machine employs other types of tractive elements such as wheels or skids as well. 
       FIG. 1  is a side elevation view of a representative power machine  100  in the form of a work vehicle upon which the disclosed embodiments can be employed. The representative power machine  100  is a work vehicle in the form of a compact track loader. However, the concepts discussed below can be practiced on many other types of work vehicles such as various types and sizes of loaders including walk behind loaders, excavators, telehandlers, trenchers, graders, dozers, and utility vehicles, to name but a few examples of the many other different types of power machines on which the disclosed embodiments can be practiced. 
     The power machine  100  includes a frame  110  that supports a power system  120 , the power system being capable of generating or otherwise providing power for operating various functions on the power machine. Frame  110  also supports a work element in the form of a lift arm structure  130  that is powered by the power system  120  and is capable of performing various work tasks. As power machine  100  is a work vehicle, frame  110  also supports a power conversion system  140 , shown in block form, which is also powered by power system  120  and is capable of providing power to work elements such as the lift arm structure  130  and tractive elements to perform various work tasks including propelling the power machine over a support surface. The lift arm structure  130  supports an implement carrier  150 , which is capable of receiving and securing various implements to the power machine  100  for performing various work tasks. The power machine  100  can be operated from an operating position  160  from which an operator can manipulate various control devices to cause the power machine to perform various functions. A control system  170  is provided for controlling the various functions of the power machine  100 . The control system  170  is shown in block form in  FIG. 1  and can include various components including electronic controllers, user input devices, hydraulic components, or any combination thereof as well as other components as may be appropriate to control various functions on a given power machine. 
     The elements of frame  110  discussed with respect to power machine  100  are provided for illustrative purposes and should not be considered to be the only type of frame that a power machine on which the embodiments can be practiced can employ. Frame  110  of power machine  100  includes an undercarriage  111  and a mainframe  112  that is supported by the undercarriage. The mainframe  112  of power machine  100  is attached to the undercarriage  111  such as with fasteners (not shown) or by welding the undercarriage to the mainframe. In other power machines on which the discussed embodiments may be practiced, the mainframe portion of the frame can be pivotally mounted to the undercarriage, such as is the case with excavators. In other power machines, the undercarriage can be integrated into the mainframe such that the undercarriage and mainframe together are part of a single frame member. Mainframe  112  includes a pair of upright portions  114 A and  114 B located on either side of the mainframe that support lift arm structure  130  and to which the lift arm structure  130  is pivotally attached. The lift arm structure  130  is illustratively pinned to each of the upright portions  114 A and  114 B. The combination of mounting features on the upright portions  114 A and  114 B and the lift arm structure  130  and mounting hardware (including pins used to pin the lift arm structure to the mainframe  112 ) are collectively referred to as joints  116  (only one of which is shown in  FIG. 1 ) for the purposes of this discussion. Joints  116  are aligned along an axis  118  so that the lift arm structure is capable of pivoting, as discussed below, with respect to the mainframe  112  about axis  118 . Other power machines may not include upright portions on either side of the frame, or may not have a lift arm structure that is mountable to upright portions on either side of the frame. For example, some power machines may have a single arm, mounted to a single side of the power machine or to a front or rear end of the power machine. Other machines can have a plurality of work elements, including a plurality of lift arms, each of which is mounted to the machine in its own configuration. Frame  110  also supports tractive elements  119 , which on power machine  100  are a pair of track assemblies one located on each side of the frame  110 , with only one track assembly  119  shown in  FIG. 1 . Other power machines on which the embodiments can be practiced can have any number and combination of tractive elements, as long as they include at least one track assembly. The track assembly  119  includes a track frame  119 A, which is coupled to or, in the case of power machine  100 , integral with the undercarriage  111 . A track  119 B surrounds the track frame  119 A. The track  119 B is driven around the track frame  119 A by a sprocket  119 C. A pair of idlers  119 D and  119 E is operably coupled to the track frame  119 A and engages the track  119 B to tension the track. Likewise, a plurality of rollers  119 F are operably coupled to the track frame  119 A and engage the track  119 B to tension the track along a support surface with which it is engaged. 
     The lift arm structure  130  shown in  FIG. 1  has a first end  132 A that is pivotally coupled to the power machine at joints  116  and a second end  132 B that moves under control of the power machine with respect to the frame  110 . The movement (i.e. the raising and lowering of the lift arm structure  130 ) is described by a travel path, which is shown generally by arrow  192 . For the purposes of this discussion, the travel path  192  of the lift arm structure  130  is defined by the path of movement of the second end  132 B of the lift arm structure. 
     The lift arm structure  130  of power machine  100  includes a pair of lift arms  134  that are disposed on opposing sides of the frame  110 . Each of the lift arms  134  includes a first portion  134 A and a second portion  134 B that is pivotally coupled to the first portion  134 A. The first portion  134 A of each lift arm  134  is pivotally coupled to the frame  110  at one of the joints  116  and the second portion  134 B extends from its connection to the first portion  134 A to the second end  132 B of the lift arm structure  130 . The lift arms  134  are each coupled to a cross member (not shown) that is attached to the second portions  134 B. The cross member provides increased structural stability to the lift arm structure  130 . A pair of actuators  138  (only one is shown in  FIG. 1 ), which on some power machines, including power machine  100 , are hydraulic cylinders configured to receive pressurized fluid from power conversion system  140 , are pivotally coupled to both the frame  110  and the lift arms  134  at pivotable joints  138 A and  138 B, respectively, on either side of the power machine  100 . The actuators  138  are sometimes referred to individually and collectively as lift cylinders. Actuation (i.e., extension and retraction) of the actuators  138  cause the lift arm structure  130  to pivot about joints  116  and thereby be raised and lowered along a fixed path indicated by travel path arrow  192 , which is generally a vertical path. A pair of control links  117  (only one is shown) are pivotally mounted to the frame  110  and the lift arm structure  130  on either side of the frame. The control links  117  help to define the vertical travel path of the lift arm structure. The lift arm structure  130  is representative of one type of lift arm structure that may be coupled to the power machine  100 . Other lift arm structures, with different geometries, components, and arrangements can be pivotally coupled to the power machine  100  or other power machines upon which the embodiments discussed herein can be practiced without departing from the scope of the present discussion. For example, other machines can have lift arm structures that are pivotally coupled to a frame that have a generally radial travel path. Other lift arm structures can have an extendable or telescoping lift arm. Still other lift arm structures can have multiple (i.e. more than two) portions segments. Some lift arms, most notably lift arms on excavators, can have portions that are controllable to pivot with respect to another segment instead of moving in concert as is the case in the lift arm structure  130  shown in  FIG. 1 . Some power machines have lift arm structures with a single lift arm, such as is known in excavators or even some loaders and other power machines. Other power machines can have a plurality of independently actuable lift arms, such as is the case with tractor loader backhoes. 
     In some power machines, including power machine  100 , the power conversion system  140  includes hydraulic components such as one or more hydraulic pumps, various actuators, and other components that are illustratively employed to receive and selectively provide power signals in the form of pressurized hydraulic fluid to some or all of the actuators used to control functional components of the power machine  100 . For example, a control valve assembly (not separately shown) is used to selectively provide pressurized hydraulic fluid from a hydraulic pump to actuators such as hydraulic cylinders that are positioned on the power machine. Power conversion system  140  also selectively provides pressurized hydraulic fluid to a port  139 , to which an implement can be coupled for receiving pressurized hydraulic fluid. Other power machines upon which the disclosed embodiments can be practiced can employ other power conversion systems. For example, some power machines have power conversion systems that include electric generators or the like to generate electrical control signals to power electric actuators. Still other power machines have mechanical transmissions that act as a power conversion system, at least so far as a drive system is concerned. 
     Power machine  100  is capable of being operably coupled to an implement  190 , which is a simple bucket. Other implements can have power devices, which are configured to receive power from the power machine  100  via port  139 . Port  139  can include a power source in the form of hydraulic fluid, but can also or alternatively include an electrical power source. Other power machines can include a mechanical power source such as power takeoff. Power machine  100  can control an attached implement either by positioning the implement, providing a power source to the implement, or both. 
     The power machine  100  includes an implement carrier  150 , which is configured to receive and secure an implement to the power machine. Implement carrier  150  shown in  FIG. 1  is pivotally coupled to the lift arm structure  130  along an axis that runs through joints  152  on each of the lift arms  134 . The pivotally coupled implement carrier  150  is positionable under control of the power machine  100  via one or more actuators. In the case of power machine  100 , a pair of hydraulic cylinders  136  (one of which is shown) are pivotally coupled to the implement carrier  150  and the lift arm structure  130  to cause the implement carrier to rotate under power about an axis that extends through the joints  152  in an arc approximated by arrow  194  in response to operator input. Hydraulic cylinders  136  are capable of receiving pressurized hydraulic fluid from the power conversion system  140  in response to actuation of operator inputs by an operator. The hydraulic cylinders  136  are sometimes referred to as tilt cylinders. 
     As mentioned above, the implement carrier  150  is configured to accept and secure any one of a number of different implements to the power machine  100  as may be desired to accomplish a particular work task. Other power machines can include different styles of implement carriers that are designed accept various different implements. Still other power machines may have lift arm assemblies without an implement carrier and instead require that implements such as a bucket are pinned directly onto the lift arm assembly. 
       FIG. 2  is a block diagram identifying components of an undercarriage  200  for a power machine that employs endless tracks as tractive elements according to the illustrative embodiments. Undercarriage  200  is generally representative of any of a number of different embodiments, including the undercarriage  119  illustrated in  FIG. 1 . Most basically, the undercarriage  200  includes a main portion  202 , which supports a main frame  204  of the power machine. Main frame  204 , in some embodiments, is integral with or rigidly mounted on, the undercarriage. One example of a power machine that has a main frame rigidly mounted on its undercarriage is power machine  100  illustrated in  FIG. 1 . Other power machines such as excavators have a main frame that is movably mounted to its undercarriage. For the purposes of this diagram, the main frame  204  refers not only to a main frame portion of the power machine, but to any other structures (cabs, lift arms, and the like) that may be attached to the main frame. 
     The undercarriage  200  includes at least track frame assembly  206 , which is coupled to the main portion  202 . The track frame assembly  206  includes a track frame  208  and track engagement components  210 . The track frame  208  can be removably attached to the main portion  202  such as with fasteners or integrated into the main portion. An integrated track frame can be welded to the main portion of the undercarriage or otherwise integrated, as opposed to being a standalone component that is attached to the main portion of the undercarriage. The track frame  208  provides a structure to carry endless tracks  212 . The track engagement components  210  are provided to engage the endless tracks  212  for providing proper tensioning on the tracks  212  as well as driving the tracks over a support surface. 
       FIG. 3  illustrates the track frame assembly  206  in more detail, showing the track frame  208  and a plurality of track engagement components  210  that engage track  212 . The track engagement components  210  include a drive mechanism  220 , which engages the track  212  to drive the track over the support surface. The drive mechanism  220  is shown as being operably coupled to the track frame  208 , but in some embodiments is actually coupled to the main portion  202  of the undercarriage  200 . Track mechanism  220 , in some embodiments, is a sprocket that is driven by a power conversion system on the power machine. 
     The track engagement components  210  can also include one or more idlers  226 , which provide the appropriate tension to the track  212 . Each of the one or more idlers  226  is coupled to the track frame  208  via an idler mounting structure  228 . In some embodiments, a pair of idlers  226  is provided to tension track  212 , with at least one of the idler mounting structures  228  being a variable tensioning device to allow for adjustment of the track tension. One or more of the idlers  226  can have idler mounting structures  228  that fix the position of such idlers to the track frame  208 . 
     In addition, track engagement components  210  can include one or more rollers  222  that engage the track to apply tension onto the support surface. Each of the one or more rollers  222  is coupled to the track frame  208  via a roller mounting structure  224 . In some embodiments, one or more of the roller mounting structures  224  can rigidly mount one or more of the rollers  224  to the track frame  208 . In other embodiments, one or more of the roller mounting structures  224  are flexible so as to provide a flexible coupling between the track frame  208  and one or more of the rollers. 
       FIG. 4  illustrates an undercarriage  300 , which is one embodiment of an undercarriage that incorporates features described generally above with respect to the undercarriage  200  of  FIGS. 2-3 . More particularly, undercarriage  300  includes idlers and rollers with idler and roller mounting structures that include advantageous features. While undercarriage  300  is described as having both of the advantageous idler and roller mounting structures, other embodiments may include the same or similar idler of either the mounting structures or roller mounting features, but not both. 
     The undercarriage  300  in  FIG. 4  is of the type that can be employed with power machine  100  and is shown without the remaining frame and tracks for the sake of clarity. Undercarriage  300  includes a main portion  302  with track frame assemblies  306  and  306 ′ on either side of the main portion  302 . Track frame assemblies  306  and  306 ′ are substantially similar and only track frame assembly  306  is described here. The undercarriage  300  shown in  FIG. 3  is a one-piece undercarriage, although in other embodiments, track assemblies of the type described here can be employed on undercarriages that are not one-piece undercarriages. For the purposes of this discussion, a one-piece undercarriage has track frames  308  that are an integral part of the undercarriage  300  as opposed to being fastened or bolted onto the undercarriage. The one-piece undercarriage  300  can be formed of a single piece of material, but multiple pieces that are welded together into a rigid assembly is also, for the purposes of this discussion, a one-piece undercarriage. The primary distinction between a one-piece undercarriage for tracked vehicles versus other undercarriages is that the track frames on one-piece undercarriages are integrated into the undercarriage instead of being removably attached to the undercarriage using bolts and fasteners. 
     The track frame assembly  306  has a variety of track engagement components with unique features, including a pair of idlers  326 A and  326 B. Idler  326 A is coupled to the track frame  308  so that it remains in a fixed position, while idler  326 B is coupled to the track frame  308  via an adjustable idler mounting structure (not shown in  FIG. 4 ) so that idler  326 B is moveable with respect to the track frame  308 . Track frame assembly  306  also includes a plurality of rollers  322 A- 322 D (collectively  322 ), each of which is coupled to the track frame  308  via flexible roller mounting structures ( 324 A- 324 D, shown in  FIG. 5 , collectively  324 ) that are mounted to the track frame  308  at mounting locations  330 A- 330 D. The flexible roller mounting structures  324 A- 324 D provide a cushioning or shock absorbing effect, which results in a smoother riding experience for an operator of a power machine that employs such roller mounting structures. In some embodiments, the roller mounting structures  324  are pre-loaded. That is, the roller mounting structures  324  are attached the track frame  308  at an angle such that the roller mounting structures  324  apply a downward force on the rollers  322  under normal conditions. Pre-loading the roller mounting structures  324  tends to reduces oscillation about an axis that is parallel an axis  344  that extends through the roller  322 D or any other of the rollers. In other embodiments, though, the roller mounting structures  324  are not preloaded. Four rollers  322  and associated roller mounting structures  324  are shown in  FIGS. 4-5 , but any number rollers can be employed in various embodiments. The roller mounting structures  324  are mounted to the track frame  308  at roller mounting locations  330 A-D such that the roller mounting structures  324 A-D are positioned inboard of the track frame. In other words, the track frame  308  provides a protective cover for the roller mounting structures  324 A-D. In addition the track frame  308  includes a plurality of engagement features  332  that are positioned to engage the rollers  322  and/or the roller mounting structures  324  to limit the upward deflection of the roller mounting structures  324 . In the embodiment shown in  FIG. 4 , the engagement features  332  are notches formed into the track frame  308  for engaging the rollers  322 . Undercarriage  300  also includes a pair of mounts  334  for carrying drive motors (not shown) which are capable of driving sprockets generally similar to the sprocket  119 C of  FIG. 1  that engage the track. 
       FIG. 5  illustrates a roller assembly  340  according to one illustrative embodiment that collectively includes roller  322  along with a pair of roller mounting structures  324 . Each of the roller mounting structures  324  is a parabolic mono-leaf spring that is attached to either side of the roller  322 . The roller mounting structures attached to each of the rollers discussed above with reference to  FIG. 4  refer to roller mounting structures  324 A-D as if a single mounting structure is provided for teach roller, which may be the case in some embodiments. However, when employing roller assembly  340 , each of roller mounting structures  324 A-D refers to a pair of roller mounting structures. The roller mounting structures  324  are attached with fasteners  336  or in any other manner that secures the roller mounting structures to the roller  322  while also allowing the roller to rotate about an axis  338  that extends through the fasteners. Fasteners  342  are shown inserted into apertures in the suspension elements  314  in  FIG. 5 , but when assembled, the fasteners are also inserted through apertures in the track frame  308  to mount the roller assembly  340  to the track frame at roller mounting locations  330 . While the embodiment in  FIG. 5  shows two roller mounting structures  324 , in other embodiments, a single or more than two roller mounting structures  324  can be employed.  FIG. 6  shows a side view of roller mounting structure  324 . The roller mounting structure  324  is a tapered spring ending in an aperture  344  through which fastener  336  is inserted to attach the roller mounting structure to the roller. One or more apertures (not shown in  FIG. 6 ) extend from a first major surface  348  to a second major surface  350  of the roller mounting structure  324 . The apertures are provided to accept fasteners  342  for attachment to the track frame  308 . In other embodiments, one or more fasteners can be pressed into roller mounting structure  324  so that the fasteners are fixed to the roller mounting structure  324  instead of being removably inserted into the roller mounting structure as fasteners  342  are. 
       FIGS. 7-8  each illustrate a portion of undercarriage  300  with portions of the track frame  308  removed to illustrate one embodiment of an idler mounting structure  400  for coupling idler pulley  326 A to the track frame  308 . In  FIG. 8 , the idler mounting structure  400  is shown in cross-section to illustrate some of its internal features. The idler mounting structure  400  is an adjustable idler mounting structure, capable of positioning the idler pulley  326 B to provide for a suitable tension on a track (not shown in  FIGS. 7-8 ). The idler mounting structure  400  includes an actuable cylinder and more particularly, a grease cylinder. Grease cylinders are generally known for use in tensioning tracks, and other types of adjustable devices can be used to tension tracks. However, the idler mounting structure  400  has several advantageous features that distinguish it over a typical idler mounting structure. 
     The adjustable idler mounting structure  400  is operably coupled to the track frame  308  at one end and to the idler pulley  326 B at a second end. The adjustable idler mounting structure  400  includes an adjustment mechanism  402 , which as mentioned above, is a grease cylinder. The grease cylinder  402  includes a cylinder body  404  that has a cavity  406  out of which a rod  408  extends on the other end. Rod  408  is a two-piece assembly with a first portion  410  that extends into cavity  406  on one end and has a cavity  412  that can accept a second portion  414  on a second end. The second portion  414  of the rod  408  is operably coupled to the idler pulley  326 B. A biasing spring  420  surrounds the second portion  414  and is captured on the second portion  414  by a pair of carriers  416  and  418 . The spring  420  biases the second portion  414  to extend the idler pulley  326 B. Under a normal tensioning condition, the second portion  414  is positioned to allow an unoccupied pocket in the cavity  412 . When a force is applied against the adjustment mechanism  402 , for example, due to shock introduced against the idler pulley  326 B, the second portion  414  is capable of retracting into the unoccupied pocket and thus absorb a shock that might occur, for example, when a tracked power machine engages uneven terrain or collides with a hard object. The adjustment mechanism  402  of this embodiment thus includes a shock absorption mechanism via the allowed movement of the second portion  414  relative to the first portion  410 , restrained by the spring  420 . 
     The second portion  414  of the rod  408  is operably coupled to the idler pulley  326 B through a ball joint  422  formed by a ball  424  located at the end of the second portion  414  and a socket  426  formed into a bracket  428  onto which the idler pulley  326 B is attached. The ball joint  422  allows for an operable coupling between the adjustment mechanism  402  and the idler pulley  326 B while also decoupling the adjustment mechanism side loads that may be introduced from the idler. 
       FIGS. 9-10  illustrate another embodiment of a track frame assembly  500  with a track  502  mounted on over a track frame  508 . The track frame assembly  500  is generally similar to the track frame assembly  306  except that roller assemblies  540  are mounted to the track frame  508  to flanges  510  so that roller mounting structures  524  are outboard of the track frame  508 . 
       FIG. 11  illustrates a cross-sectional view of an embodiment of an idler pulley  626  that can be used with track assemblies of the type discussed above. The portion of the idler pulley  626  shown in  FIG. 11  illustrates a radius  650  that joins an idler flange edge  652  with an idler rolling face  654 . The radius  650  is shaped such that it has tangency with only the idler rolling face  654  and not the idler flange edge  652 . The resulting radius  650  has advantageously prevented premature wearing of tracks by eliminating a relatively sharp edge that might otherwise chafe against a track. Prior art idler pulleys have included a small radius that achieves tangency with both the idler flange edge and the idler rolling face. 
     The embodiments discussed above introduce concepts that provide several advantages. Among those advantages are roller assemblies that are capable of providing improved suspension capabilities, resulting in improved operator comfort over prior art track suspension systems. Other advantages include an adjustable mechanism for tensioning idler pulleys that allow for improved shock absorption and capabilities of withstanding side loads. Improved idler pulleys are disclosed, which will improve the life of rubber tracks by reducing friction induced wear through engagement with an idler pulley. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.