Abstract:
A tensioning system for an endless track of a crawler-type vehicle includes an actuator, such as a dual-acting hydraulic cylinder and piston, which is coupled to a roller to translate the roller into and out of engagement with the endless track to tension or slack the endless track, respectively. The tensioning system has a mechanical stop that limits retraction of the actuator, and thus limits how much slack can be created in the endless track. The actuator automatically adds tension to the endless track when an undertensioned condition is present and automatically removes tension from the endless track when an overtensioned condition is present. To add additional slack to the endless track for removing the endless track for service, repair, or replacement, the mechanical stop may be removed which allows additional retraction of the actuator and thus disengagement of the roller from the endless track.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to an endless track tensioning system. More particularly, the invention is directed to a track tensioning system that automatically relieves tension in an endless track when the endless track encounters an obstruction and does so in a manner that limits how much slack may be introduced into the endless track but allows for the introduction of additional slack to remove the endless track for servicing and/or replacement. 
     A crawler-type work vehicle is typically supported and propelled by an undercarriage assembly having an endless track entrained about a drive roller or sprocket, a front idler roller, a rear idler roller, and a series of track rollers. The drive roller or sprocket is driven by an engine of the work vehicle which in turn causes the endless track to be advanced around each of the front and rear idler rollers as well as the track rollers to move the work vehicle in either a forward or reverse direction. 
     For the endless track to function properly, it must be tensioned taut around the several rollers. If the endless track is not properly tensioned, the track may derail from the drive sprocket or roller and the idler rollers. To this end, a tensioning mechanism is used in order to create the tension necessary to keep the track from derailing from the drive sprocket or roller and the idler rollers. In one form, the tensioning mechanism may be a coiled spring that urges the front idler roller in a direction away from the rear roller, thereby creating tension on the track. Over a period of time, a number of the components associated with the undercarriage assembly, such as the track and the idler rollers, begin to wear thereby creating slack in the track. In order to remove the slack from the track chain, it is necessary to increase the tension of the track chain to prevent undesired derailing of the track. 
     While it is generally desired to maintain tension in the track, there are times during operation of the work vehicle in which it is desired to introduce, albeit temporarily, slack into the endless track. For example, if the track of the work vehicle encounters a hard object such as a rock or stone with significant force, it is necessary to momentarily relieve the tension to ensure that the track is not damaged. Thus, a number of tensioning mechanisms are designed to momentarily relieve the tension in the track during such conditions. This is commonly accomplished by using a coiled spring that may compress somewhat to allow the idler roller to move away from the track and, as a result, relieve tension in the track until the obstacle is cleared. Once the obstacle is cleared, the track is automatically re-tensioned by the spring. 
     Typically, the spring is used in combination with a grease-type cylinder that moves the idler roller outwardly to tension the track and inwardly to introduce slack in the track in order to allow the track to be removed for servicing or replacement. The grease-type cylinder is isolated from the hydraulic system of the vehicle and is manually operated, in that an operator must stand at the vehicle and introduce grease to the appropriate side of the cylinder to extend or retract the cylinder, and must open a fitting on the opposite side of the cylinder to allow the grease to be expelled. This process is messy, wasteful and time consuming, and makes the task of changing tracks very difficult and challenging. 
     Therefore, there is a need for a track tensioning mechanism that eliminates the use of a grease cylinder and can be used in connection with the hydraulic system of the vehicle while isolating the hydraulic system from shocks experienced with the track encounters an obstacle, and which can temporarily relieve tension in the endless track when necessary without introducing undesirable excessive slack in the endless track during such conditions that could cause the track to derail. 
     SUMMARY OF THE INVENTION 
     The present invention provides a track tensioning system that tensions an endless track of a crawler-type vehicle during normal operation but can introduce slack in the endless track to prevent excessive tension in the track. The track tensioning system includes a dual-acting hydraulic cylinder in combination with a mechanical stop that limits how much slack may be introduced into the track. The dual-acting hydraulic cylinder is preferably interconnected in the hydraulic system of the vehicle, and includes a piston connected to an idler roller. The piston is operative to push the idler roller into the endless track to tension the endless track, and is operative to pull the idler roller away from the endless track to introduce slack to the endless track. The mechanical stop is positioned to limit how far the piston can be retracted when the track encounters an obstacle. In this manner, the piston is allowed to retract a certain distance to relieve tension in the track when the track strikes an obstacle, while preventing excessive slack that would cause the track to derail. The mechanical stop is removable, to allow further retraction of the piston. In this manner, the mechanical stop is removed in order to introduce sufficient slack in the endless track for removal of the endless track for repairing, servicing, or replacing. 
     It is therefore an object of the invention to provide a track tensioning system capable of introducing a limited amount of slack into an endless track during an overtensioned condition in the endless track but does so in a manner that prevents inadvertent derailing of the track. It is a further object of the invention to provide a track tensioning system that can be used with the hydraulic system of the vehicle for ease of operation, while isolating the hydraulic system from the effects of shocks experienced by the track. 
     Other objects, features, aspects, and advantages of the invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout. 
       In the drawings: 
         FIG. 1  is a pictorial view of a compact track-type vehicle having a track tensioning device according to the present invention; 
         FIG. 2  is a side elevation view of an undercarriage for a track-type vehicle as in  FIG. 1 , showing the track tensioning device of the present invention in a position at which tension is applied to an endless track; 
         FIG. 3  is an isometric view of the track tensioning device of  FIG. 2 , showing the mechanical stop in an installed, operative position; 
         FIG. 4  is an isometric of the track tensioning device similar to that shown in  FIG. 3 , showing the mechanical stop in a removed, inoperative position; 
         FIG. 5  is a partial side elevation view of the undercarriage shown in  FIG. 2  showing the endless track tensioning device with the mechanical stop in the installed, operative position as in  FIG. 3  to tension the track while allowing slight retraction of the cylinder to temporarily remove tension from the endless track; and 
         FIG. 6  is a partial side elevation view of the undercarriage shown in  FIG. 2  showing the endless track tensioning device with the mechanical stop in the removed, inoperative position as in  FIG. 4  to allow retraction of the cylinder to remove the endless track from the roller. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to  FIG. 1 , a track-type vehicle  10 , e.g., a compact track loader, has an operator cab  12  supported by a chassis  14 . A pair of arms  16 ,  18  are connected to the chassis  14  and are designed to lift and lower bucket  20  as known in the art. In addition, a pair of hydraulic actuators  22 ,  24  are mounted to the chassis  14  and are operative to tilt the bucket  20  when desired as also known in the art. It is understood that the specific construction of the vehicle  10  is not relevant to the present invention, and that the present invention may be used with any type of vehicle that is propelled using a track driven by a roller system. 
     An undercarriage  26  is secured to the chassis  14  in a known manner and includes a front idler roller  28 , a rear idler roller  30 , a drive roller  32 , and track rollers  34  as is generally known in the art. An endless track  36  is entrained around the idler rollers  28 ,  30 , drive roller  32 , and track rollers  34 . One skilled in the art will appreciate that the undercarriage  26  supports another set of rollers on the opposite side of the vehicle  10  and that another endless track  38  is entrained thereabout. In this regard, the crawler-type vehicle  10  is driven by a pair of endless tracks  36 ,  38  to advance the vehicle  10 . 
     As known in the art, the drive roller  32  is connected to the engine (not shown) of the vehicle  10  and engages the endless track  36  to cause translation of the endless track  36  when the drive roller  32  is rotated by the engine. The drive roller  32  may have teeth that engage within recesses in the track  36 , or the track may have teeth that are engaged within recesses in the drive roller  32 . In either configuration, the drive roller  32  can be rotated in either a clockwise or a counterclockwise direction to move the vehicle  10  in either a forward or reverse direction. 
     Referring now to  FIG. 2 , a track tensioning mechanism  40  in accordance with the present invention is supported by the undercarriage  26  and is operative to tension the endless track  36  around the idler rollers  28 ,  30  and the drive roller  32 . A relatively taut engagement of the track  36  around the rollers  28 ,  30  and the drive roller  32  is necessary to prevent derailing of the endless track  36  and for generally consistent advancement of the vehicle  10 . The track tensioning mechanism  40  is generally comprised of an actuator  41  that is preferably a dual-acting hydraulic cylinder  42  having an extendable and retractable piston  44  that is linked to the front idler roller  28 . 
     The front idler roller  28  rotates around an axle  46  and a bracket  48  is connected between the axle  46  and the piston  44 . As shown particularly in  FIGS. 3 and 4 , the bracket  48  includes mounting arms  50 ,  52  mounted adjacent opposite sides of the idler roller  28 . The arms  50 ,  52  are interconnected by a bridge  54  that is connected to the piston  44  by a coupler  55 . 
     The hydraulic cylinder  42  is flow-coupled to the hydraulic system (not shown) of the vehicle  10  and is operative to extend and retract the piston  44  based on a desired tensioning of the endless track  36 . When the piston  44  is extended, the idler roller  28  is pushed into engagement with the endless track  36  and tightens the endless track  36  around the rollers. On the other hand, when the piston  44  is retracted, slack is introduced into the endless track  36 . The present invention provides a track tensioning mechanism  40  that limits how far the piston  44  may be retracted and thus how much slack may be introduced into the endless track  36 . 
     A mechanical stop  56  is mounted to a side of the cylinder  42  and includes a mounting flange  58  that has a generally planar surface  60  from which spaced and parallel legs  62  axially extend. As shown in  FIG. 3 , the legs  62  abut against the face  63  of the cylinder  42 . The flange  58  is mounted to the cylinder  42  by a pair of fasteners  64 , e.g., bolts. A space (not numbered) is defined between the legs  62  and is sized to receive the piston  44  so that the piston  44  can slide longitudinally between the legs  62  when extending and retracting the idler roller  28 . The mechanical stop  56  may be removed by unfastening fasteners  64 , which will allow further retraction of the piston  44 . As will be described more fully below, the legs  62  limit how far the piston  44  may be retracted when relieving tension in the endless track  36 . 
     Referring now to  FIGS. 2 ,  5  and  6 , it will be appreciated that the track tensioning mechanism  40  provides three general modes of operation. In a first mode, illustrated in  FIG. 2  and corresponding to normal traveling conditions for the vehicle  10 , the piston  44  is extended to push the front idler roller  28  into engagement with the endless track  36 . The longer the piston  44  is extended, the more tension created in the endless track  36 . Thus, as the endless track  36  elongates over time, more extension of the piston  44  can be provided in order to keep the endless track  36  taut. 
     In a second mode, illustrated in  FIG. 5 , the piston  44  is retracted a limited amount to introduce slack into the endless track  36 . The piston  44  may be retracted under the force of an impact, such as when the track  36  encounters an obstacle, or may be retracted by the operator to relieve tension in the track, such as for cleaning, debris removal, etc. The piston  44  may also be retracted to relieve tension in the endless track  36  when the vehicle  10  is parked. In this second mode, retraction of the piston  44  is limited by the mechanical stop  56 . More particularly, the piston  44  cannot be further retracted when the bridge  54  abuts the legs  62  extending from flange  58 . The mechanical stop  56  is mounted to the cylinder  42  and is configured such that the maximum amount of slack that may be introduced into the endless track  36  with the stop  56  in place is not enough to allow the endless track  36  to derail. In this mode, engagement of the endless track  36  with the rollers is sufficiently maintained to prevent removal of the endless track  36  from the undercarriage  26 . 
     However, in a third mode illustrated in  FIG. 6 , the mechanical stop  56  is removed so that the piston  44  can be fully retracted to introduce sufficient slack in the endless track  36  that allows the endless track  36  to be removed from the undercarriage  26 . Thus, to service, repair, or replace the endless track  36 , the mechanical stop  56  is removed and the hydraulic system of the vehicle  10  is then operated to fully retract the piston  44 . As shown in  FIG. 6 , when the piston  44  is fully retracted, the front idler roller  28  is completely disengaged from the endless track  36 . In this position, the endless track  36  is sufficiently slacked to be removed from the undercarriage  26 . Similarly, when installing an endless track  26 , the mechanical sop  56  is preferably removed to provide full retraction of the piston  44  and thus the front idler roller  28 . Once the endless track  36  is installed, the piston  44  is extended to tension the endless track  36  and the mechanical stop  54  is then re-fastened to the cylinder  42 . 
     As noted above, the cylinder  42  is preferably a dual-acting hydraulic cylinder that is fluidly coupled with the hydraulic system of the vehicle. This allows a user to extend and retract the piston  44  using operator controls (not shown) in the operator cab  12 . Additionally, the cylinder  42  is allowed to retract slightly to the position shown in  FIG. 5  when the endless track  36  experiences an impact or encounters an obstacle. The hydraulic pressure in the cylinder  42  causes automatic extension of the piston  44  to maintain a relative uniform tension in the endless track  36  during normal operation. The mechanical stop  54  prevents the piston  44  from retracting excessively during such conditions, which maintains the track  36  on the rollers and also isolates the hydraulic system from excessive sudden increases in pressure that could otherwise occur. 
     The removable mechanical stop  54  is shown and described as being fully removable from the piston  44 . It should be appreciated, however, that the stop may also be configured such it is movably mounted to the vehicle  10  and does not have to be completely removed in order to allow the piston to fully retract. For example, the stop  54  may be interconnected with the vehicle using a pivoting or sliding connection, which allows the stop  54  to be selectively moved between the operative and inoperative positions. In this alternate connection, the mechanical stop  54  does not need to be fully removed from the undercarriage  26  to slack the endless track  36  sufficiently for track removal. It will be appreciated that a tensioning mechanism such as that described herein may be used to move the rear idler roller instead of, or in addition to, the front idler roller. 
     Various alternatives and embodiments are contemplated as being within the scope of the following claims, which particularly point out and distinctly claim the subject matter regarded as the invention.