Abstract:
A track type work machine is provided including a roller frame having a rotatable idler mounted at an end thereof. A gas spring is operable to absorb selected loads on the idler, and is isolated from loads transverse to a reciprocation axis of the gas spring by a recoil system. A method of providing for load absorption from the idler is also provided. The method includes positioning a gas spring between the idler and a roller frame of the work machine, and operably coupling the idler to the gas spring to selectively transmit loads from the idler thereto.

Description:
TECHNICAL FIELD 
   The present disclosure relates generally to track type work machines, and relates more particularly to an idler recoil system for a track type work machine having a gas spring operable to absorb selected loads on the idler. 
   BACKGROUND 
   Track type work machines are in widespread use in construction, mining, forestry, and similar industries. In particular, bulldozers, cranes and pavers are commonly seen track type work machines along roads, freeways and at construction sites. “Tracks” rather than wheels are typically used on work machines operating in environments where creating sufficient traction with conventional tires is problematic or impossible. Rather than rolling across a work surface on wheels, track type work machines utilize one or more tracks extending about a plurality of rolling elements. Such tracks are typically made up of a loop of coupled metal links having outer sides that engage the ground or work surface, and inner sides travelling about the rolling elements, which can include various drive rollers, support rollers, tensioners and “idlers.” 
   An idler in a track type work machine is a rolling element that passively rolls against the track and supports the inner side of the track as it rolls about the idler. Traditionally, idlers included a smooth cylindrical outer surface that rolled along rails defined by the individual track links, or by the idler itself. Newer designs, however, often include a plurality of teeth that engage against the bushings that join the track links, similar to a gear wheel. 
   While contemporary idler designs offer numerous advantages over traditional, non-toothed idlers, they have given rise to various new problems and engineering challenges. Over the course of work machine operation, debris can more readily find its way between a toothed idler and track links than in a traditional design. As a result, debris such as a rock can actually become lodged between a portion of a track link and the teeth, or pockets between the teeth, of the rotating idler. Similar problems are associated with the toothed sprocket and track on the roller frame opposite the idler. 
   Lodging of a rock between the idler or sprocket and the track can effectively lengthen the distance traversed by the track, and/or increase the tension thereof having two possible outcomes. First, if the work machine track components are sufficiently robust, the rock will be crushed. Alternatively, the rock may actually strain the track and associated components to the point at which something breaks. 
   In an attempt to avoid the rock-crushing, track-breaking alternatives, designers have developed a variety of means to allow debris to simply roll through, for example by actually recoiling the idler, to lower or maintain the track tension. One design incorporates a coil spring with the track roller frame. The coil spring is positioned such that it can absorb recoil forces on the idler, such as while a rock is lodged between the idler or sprocket and the track. In general, it is desirable to limit the frequency of recoil events in the track system, as they tend to lead to excessive wear of the components. With a coil spring, recoil frequency would generally be limited by utilizing a coil spring having a relatively high spring constant such that it will only be compressed when a recoil force above a certain threshold is encountered. 
   While such a design is relatively simple, a particularly large, heavy-duty coil spring can be necessary to provide sufficient resistance to recoil. 
   In many work machine designs, known coil springs having a sufficient spring constant may not actually fit into the track roller frame, therefore being difficult or impossible to utilize. Such coil springs must also typically be surrounded by a steel structure on the roller frame for safety and protection of the spring itself. Further still, coil springs made of common known materials may not have a sufficiently linear spring force as a function of the degree of compression. In other words, it may become exceedingly difficult to further compress a coil spring when it is close to full recoil, confounding its intended purpose. 
   In recent years, designers have proposed various alternatives to the aforementioned coil spring designs, some meeting with significant success. One example of a non-coil-spring idler recoil design incorporates a combined pneumatic and hydraulic system to absorb loads on the idler. In such a design, recoil forces on the idler are absorbed by displacing hydraulic fluid, and simultaneously compressing gas in an accumulator. While these more modern designs offer certain advantages over coil spring designs, they must typically be connected with the work machine hydraulic system, requiring hydraulic lines to extend between the track assembly and the work machine body, a design that is both complex and apt to require frequent maintenance. One particular design utilizes a gas accumulator mechanically linked with the idler to absorb recoil forces thereon. U.S. Pat. No. 6,682,155 to Hoff, et al. is directed to one such system. Hoff, et al. describe a track tension adjustment actuator, operable to selectively reduce tension on the idler wheel in a track type work machine, especially when the work machine is traveling. The actuator of Hoff, et al. includes a hydraulic cylinder housing, and a recoil piston disposed within the cylinder housing and coupled with the idler wheel. The cylinder housing and recoil piston form a recoil chamber that is pressurized to urge the recoil piston away from the work machine drive wheel, tensioning the track. Another known design is described in U.S. patent application Ser. No. 10/325,362, now abandoned. The &#39;362 disclosure is directed to a track tension adjustment mechanism, in particular a system, like Hoff, et al., wherein tension on an idler wheel of a track type work machine is reduced when the machine is traveling. The &#39;362 disclosure includes a track tensioning system having an idler wheel, a drive wheel, and a drive track. A hydraulic motor is operable to advance the drive wheel, and an actuator having a recoil chamber is coupled with the idler wheel to urge the idler wheel away from the drive wheel and thereby tension the track. A controlled quantity of hydraulic fluid may be delivered to the actuator to adjust the track tension as needed. 
   While the above systems offer various advantages, particularly in that a relatively smaller, simpler recoil system can be made, high pressure gas accumulators have inherent sealing problems, particularly where they are subjected to side loads on pistons therein. 
   The present disclosure is directed to one or more of the problems or shortcomings set forth above. 
   SUMMARY OF THE INVENTION 
   In one aspect the present disclosure provides a track type work machine including, a roller frame and a rotatable idler mounted proximate an end of the roller frame. The idler is movable along a recoil axis with respect to the roller frame. A plural component recoil system is operably positioned between the roller frame and the idler, and includes a gas spring having a reciprocation axis aligned with the recoil axis. The gas spring is coupled with the idler and operable to absorb selected loads thereon, at least one component of the recoil system having a laterally movable interface with another component of the recoil system. Lateral movement isolates the gas spring from loads transverse to the reciprocation axis. 
   In another aspect, the present disclosure provides an idler recoil system for a recoil machine including an idler yoke, and a reciprocable shaft. The shaft includes a longitudinal axis and is coupled with the idler yoke at a contact joint. The contact joint includes adjacent joint surfaces laterally movable relative to one another to isolate the shaft from selected loads on the idler yoke. A gas spring is provided having a reciprocation axis aligned with the longitudinal axis, the gas spring being operable to absorb loads transmitted to the shaft from the idler yoke. 
   In yet another aspect, the present disclosure provides a method of providing for load absorption from an idler in a track type work machine. The method includes the steps of operably positioning a gas spring between the idler, and a roller frame of the work machine to absorb loads on the idler in a direction aligned with a reciprocation axis of the gas spring. The method further includes the step of isolating the gas spring from loads transverse to the reciprocation axis. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view in perspective of a work machine according to the present disclosure; 
       FIG. 2  is a perspective view of an idler recoil system for a work machine according to the present disclosure; 
       FIG. 3  is also a perspective view of an idler recoil system according to the present disclosure; 
       FIG. 4  is a schematic view of an idler recoil system according to the present disclosure; and 
       FIG. 5  is a schematic view of an adjuster guide configuration suitable for use in an idler recoil system according to the present disclosure. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , there is shown a track type work machine  10 , for example a tractor or bulldozer, in accordance with a preferred embodiment of the present disclosure. Work machine  10  includes a work machine body  12  having a track assembly  14 . A drive sprocket  20  is disposed at one end of track assembly  14  and is operable to drive a track  15  to propel work machine  10 . An idler  16  is mounted proximate an end of a roller frame  22  and rotates against track  15  at an end of track assembly  14 , in a conventional manner opposite drive sprocket  20 . A recoil system  40 , shown in phantom, is mounted to roller frame  40  and is operable to absorb recoil loads on idler  16 , as described herein. 
   Turning to  FIG. 2 , there is shown in perspective recoil system  40  of  FIG. 1 , mounted to roller frame  22 . In a preferred embodiment, recoil system  40  includes an idler yoke  42  configured to support idler  16  in support blocks  43 , although alternative supporting and/or mounting means for idler  16  are possible. A rod, or recoil shaft  52  is disposed adjacent idler yoke  42  and transmits loads thereon through recoil system  40 , as described herein. Idler yoke  42  is preferably movable in directions transverse to a longitudinal axis L of shaft  52 , to absorb vertical, sideways, and twisting loads on idler  16 , in a conventional manner. An adjuster  44 , for example an hydraulic adjuster, is preferably disposed adjacent shaft  52 , and is operable to adjust the position of idler yoke  42 , and hence idler  16 , relative to a gas spring  46 . In a preferred embodiment, adjuster  44  includes both a fluid inlet and a fluid outlet (neither shown) to allow the introduction or evacuation of hydraulic fluid there from, correspondingly adjusting idler  16  forward or backward. Idler  16  is in contact with track  15 , and adjustment thereof with adjuster  44  can therefore adjust a track tension of track assembly  14 . 
   Gas spring  46  may be any suitable sealed gas container, and preferably includes a piston  54 , which may be thought of as a second recoil shaft, adjacent adjuster  44 . In a preferred embodiment, a recoil axis R of gas spring  54 , also an axial centerline of piston  54 , is aligned with longitudinal axis L of shaft  52 . Further, recoil axis R is preferably intersecting and orthogonal to a line extending through an axis of rotation of idler  16 , preferably when idler  16  is at a center, rest position. Gas spring  46  may be pressurized with any suitable compressible fluid, for example, nitrogen or air. Referring also to  FIG. 3 , gas spring  46  is preferably mounted to roller frame  22  with one or more metallic straps  48  or similar devices, allowing relatively easy removal from recoil system  40 . Thus, when a leaky, insufficiently pressurized or otherwise faulty gas spring needs to be replaced, it is decoupled and removed from roller frame  22  by unfastening straps  48 . 
   A spacer  49  is further preferably provided, and disposed between gas spring  46  and an end of roller frame  22 . Spacer  49  is provided to transmit forces or loads on gas spring  26  to roller frame  22 , and is preferably equipped with one or more mounting apertures  49  for bolting the same to roller frame  22 . In a preferred embodiment, mounting apertures  49 , and the mounting bolts therewith, are configured having a relatively large tolerance, allowing spacer  49  to move slightly relative to roller frame  22  and avoid shearing the bolts connecting the same therewith. 
   Adjuster  44  is preferably rectangular, and reciprocates relative to roller frame  22 . Adjuster  44  is preferably guided in an adjuster guide  45  having a pair of guide plates  45   a  and  45   b  at opposite sides thereof, preferably via a grooved engagement therewith. As used herein, the term “grooved engagement” should be understood to refer to a design wherein at least one of guide plates  45   a  and  45   b , or adjuster  44  includes one or more grooves  41 .  FIGS. 3 and 5  illustrate grooves  41  in adjuster  44 . Each of the one or more grooves  41  slidably engages with a mating feature on the other of adjuster  44  or guide plates  45   a  and  45   b , for example an edge of guide plates  45   a  and  45   b . In a preferred embodiment, grease is placed at the interface of groove(s)  41  and guide plates  45   a  and/or  45   b . The described engagement restricts rotational movement of adjuster  44  and lateral displacement of the same during recoil of idler  16 . In a preferred embodiment, one of adjuster  45  and roller frame  22  is equipped with a stop  55  that restricts displacement of adjuster  44  in a recoil direction past a predetermined point. Thus, when idler  16  experiences a sufficient load transmitted to adjuster  44  and thenceforth to gas spring  46 , adjuster  44  will reach a maximum point of retraction, against stop  55 . This feature can prevent overpressurization of gas spring  46  by limiting the extent of recoil of piston  54 . 
   Gas spring  46  is operable to absorb only selected loads, along axis R. Sideways, vertical and twisting movements of idler  16  are preferably isolated from gas spring  46 , to the extent they are transferred into recoil system  40 . In a preferred embodiment, at least one contact joint is located between idler yoke  42  and gas spring  46 , to transmit loads to gas spring  46  along the reciprocation axis thereof. As used herein, the term “contact joint” should be understood to refer to a mechanical coupling wherein two adjacent members include surfaces positioned in contact with each other, but not physically attached. In a preferred embodiment, shaft  52  and idler yoke  42  each define a portion of a contact joint  63  therebetween, for example, including a convex surface on one of the idler yoke  42  and shaft  52 , and a flat or similar shape adjoining the convex surface and disposed on the other component. Accordingly, idler yoke  42  will transmit force or loads to shaft  52  substantially only along axis L. The transfer of loads on idler  16  transverse to the longitudinal axis L of shaft  52  and/or the reciprocation axis R of gas spring  46  will most preferably be negligible. This is possible because the convex-flat interface of joint  63  will allow one of the components to slip laterally relative to the other rather than transmitting a transverse or twisting load. Similarly, because shaft  52  and idler yoke  42  are not physically attached, any loads on idler  16  that tend to extend the same, rather than recoiling, will not be transferred to shaft  52 . Shaft  52  may be likewise coupled with adjuster  44  via a contact joint  62 , having a similar configuration. A third contact joint  61  is also preferably disposed between piston  54  and adjuster  44 , preferably being defined in part by each of the same. It should be appreciated that the term “contact joint” refers generally to any mechanical coupling wherein lateral load transmission is small or nonexistent, but axial load transmission is possible in at least one axial direction. 
   INDUSTRIAL APPLICABILITY 
   Referring to the drawing figures generally, idler recoil system  40  is preferably operable when a load on idler  16  sufficient to compress gas spring  46  is encountered. In a preferred embodiment, gas spring  46  is pressurized to a degree such that a load approximately equal to the work machine weight is necessary to initiate compression thereof. In many standard work machine designs, the track assembly is designed and configured such that the tracks are strong enough to support a load equaling the weight of the work machine before breaking. The actual pressurization of gas spring  46  may therefore be slightly less than that corresponding to the vehicle weight such that idler  16  will begin to recoil prior to breaking the tracks. 
   Gas spring  46  is also preferably equipped with a gas exchange valve (not shown) such that its pressurization can be adjusted, allowing recoil system  40  to accommodate different selected loads, depending upon operating conditions. A further advantage of both the adjustability of the pressurization of gas spring  46 , and its being readily replaceable, is that recoil system  40  can operate as desired over a range of different temperatures. The relative pressurization of gas spring  46  can vary significantly between a cold environment such as Antarctica, and a hot environment close to the equator, and adjustment of gas spring  46 , or switching with another gas spring may be desirable. Moreover, the rigidity of the components of track assembly  14  can also vary with temperature, and thus the necessary force to break the track, and desired force necessary to begin compression of gas spring  46  can both vary. 
   During operation, rocks or other debris may become trapped between idler  16  or sprocket  20  and track  15 . As debris is drawn into the loop of track  15 , the tension on track  15  increases. Where this tension increase is less than an approximate weight of work machine  10 , gas spring  46  will remain in a maximally extended state, stretching track  15  or crushing the debris. Where the track tension approaches the work machine weight, however, gas spring  46  will begin to compress, absorbing a load along reciprocation axis R. Contact joints  61 ,  62  and  63  transfer a load on idler  16 , also on idler yoke  42 , rearward in recoil system  40  to adjuster  44  and ultimately gas spring  46 . Because the respective contact joints preferably negligibly transfer loads transverse to axes R and L of gas spring  46  and/or shaft  52 , respectively, vertical, twisting and side loads on idler  16  are isolated from gas spring  46 , protecting the sealing thereof. 
   As a recoil event progresses, un-crushed debris between track  15  and idler  16  or sprocket  20  will be passed out, and as the load on gas spring  46  drops below the approximate work machine weight, gas spring  46  will re-extend adjuster  44  and idler yoke  42  to restore the components to a normal working condition. 
   It has been generally found that higher gas spring preloads are desirable than in many earlier designs. Thus, wear of the various components of recoil system  40  will be reduced by limiting the frequency of recoil events with a more highly pre-loaded gas spring, and the frequency with which debris is crushed will be increased. 
   The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the spirit and scope of the present disclosure. For example, although the described convex-flat interface in joints  61 ,  62  and  63  is preferred, other types of component interfaces are contemplated, for example, where both surfaces are convex or hemispheric. Further, the respective components might be linked together, so long as lateral load transmission is minimized. Other aspect, features and advantages will be apparent upon an examination of the attached drawing Figures and appended claims.