Abstract:
An undercarriage is disclosed that includes a rigidly mounted track roller near or adjacent to a rear drive sprocket, with the outer radius of the track roller overlapping the outer radius of the drive sprocket. The remaining rollers and bogies may be flexibly suspended.

Description:
FIELD OF THE INVENTION 
     This disclosure relates to track rollers for undercarriage bogies and, more particularly, to rigidly mounted track rollers. 
     BACKGROUND OF THE INVENTION 
     It is conventional to provide undercarriage track rollers and bogies with suspension elements to absorb shock and improve weight distribution as exemplified in U.S. Pat. No. 7,025,429 (see  FIG. 5 ). As illustrated in  FIG. 5 , one end of the track frame  1  is provided with a yoke  1   a  to a distal end of which a track idler  2  is rotatably mounted. A sprocket wheel  3  is rotatably mounted on a vehicle body (not shown) in the vicinity of an opposite end portion of the track frame  1 . A plurality of track rollers  11 ,  12 ,  43 , and  47  are attached in individually rocking manners to a lower portion of the track frame  1  between the idler  2  and the sprocket  3 . An endless track chain  6  is trained about the idler  2 , sprocket  3  and track rollers  11 ,  12 ,  43 , and  47 . Below the track frame  1  at a location adjacent the idler  2  is a roller unit  40   a  including an arm  41  having a forward end portion attached to the track frame  1  for rocking vertically about a pin  42 . On abutment portions of an upper portion of the arm  41  and a lower location of the track frame  1 , respectively, there is mounted elastic members  44   a  and  44   b  which abut against each other to restrict upward movement of the arm  41  and to bear the load applied to the track roller  43  to absorb the impact, which might otherwise be received by the track roller  43 . Similarly, mounted below the track frame  1  adjacent to sprocket  3  there is a single track roller unit  40   b  including an arm  45  having its proximal end portion vertically pivotally attached to the lower portion of the track frame  1  for being rocked about a pin  46 . Respectively mounted on an upper rear end portion of the arm  45  and a lower portion of the track frame  1  are elastic members  48   a  and  48   b  which abut against each other to limit upward pivoting of the arm  45  and to bear the load applied to the track roller  47  to thereby absorb the impact, which might otherwise be received by the track roller  47 . In addition, a predetermined number of double track roller units  10  are disposed below the track frame  1  between the track rollers  43  and  47 , with each roller unit  10  including a first arm  31  having a proximal end portion attached to the lower portion of the track frame  1  for being rocked vertically on a first pin  33 , and a second arm  32  having a central portion mounted to the distal end portion of the first arm  31  for being vertically rocked about a second pin  35 . Elastic members  34   a  and  34   b  are respectively mounted to the upper portion of the first arm  31  and the lower portion of the frame  1  so that they abut each other and act to restrict upward pivotal movement of the arm  31  and bear the load applied to the lower rollers  11  and  12  to thereby absorb the impact which might otherwise be transferred to the roller  11  and  12 . Thus, the roller  43  adjacent the idler  2 , the rollers  11  and  12  of the double track roller units  10  and the roller  47  adjacent to the drive sprocket  3  are all suspended. This practice, when extended to track roller adjacent to the drive sprocket, can lead to damage and avoidable wear of the drive sprocket. Further, under load conditions, the rear drive sprocket pulls on the track to propel the crawler in a forward direction, drawing the track taut and, essentially, negating the need for the roller nearest the drive sprocket to be provided with costly suspension. 
     SUMMARY OF THE INVENTION 
     Disclosed herein is an undercarriage that may include a rigidly mounted roller near or adjacent to a rear drive sprocket. The remaining rollers and bogies may be flexibly suspended. Comparatively, the rigidly mounted roller may, among other things, serve to improve vehicular weight distribution across the track, reduce the number of parts in the undercarriage, increase protection from debris entering the tooth area of the drive sprocket and reduce ground or shock loads to the final drive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a vehicle that may make use of the invention; 
         FIG. 2  is a side view of a frame and a portion of an undercarriage making use of the invention; 
         FIG. 3  is a side view of a portion of the undercarriage that is not rotated with respect to the frame; 
         FIG. 4  is a side view of the portion of the undercarriage of  FIG. 3  that is rotated with respect to the frame; and 
         FIG. 5  is a side view of the undercarriage; and 
         FIG. 5  is a side view of a prior art undercarriage as disclosed in U.S. Pat. No. 7,025,429. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is an illustration of a work vehicle in which the invention may be utilized. The dozer  10  illustrated, includes a cab  20 , a body  30 , a main frame  40 , and an undercarriage  100 . 
       FIG. 2  illustrates a side view of a portion of the undercarriage  100  as well as a portion of the main frame  40  and a rear drive sprocket  50  rigidly attached to the main frame  40  via a gearbox (not shown). As illustrated, the undercarriage  100  includes: a track frame assembly  200  having a first or stationary portion  200   a  and a second or moving portion  200   b ; an idler bogie arm  210  pivotally attached to the moving portion  200   b  at pivot point  211 ; an idler  215 , rotationally attached to a first end  210   a  of the idler bogie arm  210  at  216 ; a first flexible pad  212  attached to a second end  210   b  of the idler bogie arm  210 ; a first minor bogie arm  214 , pivotally attached at the second end  210   b  of the idler bogie arm  210  at pivot axis  213 . Also illustrated is a first roller bogie arm  220  pivotally attached at a first end  220   a  to the stationary portion  200   a  at pivot shaft  221 ; a second flexible pad  222  attached to a second end  220   b  of the first roller bogie arm  220 ; a second minor bogie arm  224 , pivotally attached to the second end  220   b  of the first roller bogie arm  220  at pivot axis  223 . The illustration further includes a second roller bogie arm  230  pivotally attached, at a first end  230   a  to the stationary portion  200   a  at pivot shaft  231 ; a third flexible pad  232  attached to a second end  230   b  of the second roller bogie arm  230 ; a third minor bogie arm  234 , pivotally attached to the second roller bogie arm  230  at pivot shaft  233 . Two rollers  217  are rotationally attached to each of the minor bogie arms  214 ,  224  and  234  in a conventional manner and rotate about their respective axes  215 ′. The flexible pads  212 ,  222  and  232  may be made of an elastomeric material and may be conventionally attached to the idler bogie arm  210  and the first and second roller bogie arms  220 ,  230  and the stationary portion as described. Stationary flexible pads  212 ′,  222 ′ and  232 ′ may be similarly attached to the stationary portion  200   a  of the track frame assembly  200  and positioned such that contact is maximized with their respective mating flexible pads  212 ,  222  and  232  as the second ends  210   b ,  220   b  and  230   b  move closer to the stationary portion  200   a . Additionally, the flexible pads  212 ′,  222 ′ and  232 ′ may also be made of an elastomeric material. As illustrated, a fixed roller  300 , which is the same in size and construction as the rollers  217 , is rotationally attached to the track frame assembly  200  at fixed roller rotational axis  301  where the fixed roller rotational axis  301  is rigidly located with respect to the track frame assembly  200 . As shown in  FIGS. 3 and 4 , the undercarriage  100  also includes a track chain  101 . Note that only one track frame assembly  200  is illustrated in the Figures, with the track frame assembly  200  on the other side of the vehicle  10  being an identical reflection of the illustrated track frame assembly  200 . 
     As illustrated in  FIGS. 2 ,  3  and  4 , the track frame assembly  200  and the main frame  40  are pivotally connected together via a pivot shaft  201 . As illustrated, a drive sprocket  50  may be rotationally connected to the main frame  40  via a final drive (not shown) and conventional housing structure (not specifically illustrated) and may rotate about an axis  51  having a fixed location with respect to the main frame  40 . The track frame assembly  200  may be slidably connected to a support bar (not illustrated). The support bar (not illustrated) may be pivotally connected to the main frame  40  midway between the track frame assemblies  200  at the opposite sides of the undercarriage  100  and may limit the angular range of rotation for each track frame assembly  200  about the pivot shaft  201  to a maximum angular range of, for example, ±3°. 
     As the vehicle moves along irregular areas of the ground, the roller bogie arms  220 ,  230  as well as the idler bogie arm  210  may pivot upon their respective axes  221 ,  231  and  211  in accordance with the demands of the terrain and the weight of the vehicle  10 . Additionally, attached rollers  217  rotate about their respective axes  218  and the minor bogie arms  214 ,  224 ,  234  pivot about their respective axes  213 ,  223 ,  233  to accommodate irregularities as the weight of the vehicle  10  causes the track chain  101  to bend and conform to the contours of the ground. 
     As illustrated in  FIG. 2 , the fixed roller  300  does not flex, with respect to the track frame assembly  200 , to accommodate the contours of the ground as it has an axis  301  that is rigidly fixed with respect to the track frame assembly  200 . Additionally, the fixed roller  300  is placed as close as practicable to the drive sprocket  50 . In fact, it can be seen that when the work vehicle is on level ground, as indicated by a reference line L, and outer radius R 1  of the fixed roller  300  overlaps an outer radius R 2  of the sprocket  50  by a distance X min  (see  FIG. 3 ), with it being noted that this outer radius of the fixed roller  300  is defined by an end rim portion which overlaps the track chain  101 . The proximity of the fixed roller  300  to the drive sprocket  50  results in the fixed roller  300  preventing a significant amount of debris from reaching the drive sprocket as the fixed roller will tend to crush and remove such debris prior to its contact with the drive sprocket  50 . The fixed roller  300  also acts to reduce the amount of weight and shock loading borne by the drive sprocket  50  because it is able to bear a substantial portion of any load in that location, including a weight of the track frame assembly  200 , due to its proximity to the drive sprocket  50 . 
     As illustrated in  FIG. 2 , the horizontal reference line L extends beneath an axis of the pivot shaft  201  and the drive sprocket axis  51 , with the pivot shaft  201  being spaced from the reference line L by a distance Y 1  and the drive sprocket rotational axis  51  being spaced from the line L by a distance Y 2  and thus they are approximately equidistant from the ground, i.e., Y 1 ≈Y 2 . Such an arrangement allows a minimal distance between the fixed roller  300  and the drive sprocket  50  and results in improved weight distribution as described above. 
       FIG. 4  illustrates the track frame assembly  200  at a maximum angular position of 3° with respect to the main frame  40 , i.e., 3° in a direction that reduces the distance between the roller  300  and the sprocket  50  thereby increasing the overlap between the outer radius R 1  of the fixed roller  300  and the outer radius R 2  of the drive sprocket  50 . (Note:  FIGS. 2 and 3  show the track frame at an angular position of 0° with respect to the main frame.  FIG. 2  illustrates R 1  and R 2 .) In this exemplary embodiment of the invention, a maximum overlap distance X max  X min , as shown in  FIG. 4 , exists between the roller radius R 1  and the sprocket radius R 2 , at the maximum angular position illustrated, for non-interference between the fixed roller  300  and the drive sprocket  50 . Thus, the track frame assembly  200 , the main frame  40  and the drive sprocket  50  may be designed such that the maximum overlap distance X max  between the outer radius R 1  of the roller  300  and the outer radius R 2  of the sprocket  50  occurs at the maximum angular position of 3°. Such a design results in the minimum practicable overlap distance X min  between R 1  and R 2  at an angular position of 0°. 
     As described above and illustrated in  FIGS. 3 and 4 , the fixed roller rotational axis  301  moves with respect to the drive sprocket rotational axis  51  whenever the track frame assembly  200  rotates with respect to the main frame  40  about pivot shaft  201 . As described earlier rotational movement between the track frame assembly  200  and the main frame  40  for this exemplary embodiment may be restricted to a predetermined angular range of, for example, ±3°. Thus, in order to place the fixed roller  300  as close as practicable to the drive sprocket  50 , the fixed roller  300  may be placed such that it avoids interference with the movement of the drive sprocket  50  when the relative angle between the main frame  40  and the track frame assembly  200  is at its maximum (e.g., 3°) in a direction that reduces the distance between the fixed roller  300  and the drive sprocket  50 . 
     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.