Abstract:
An undercarriage is disclosed that may include a rigidly mounted roller near or adjacent to a rear drive sprocket. The remaining rollers and bogies may be flexibly suspended.

Description:
FIELD OF THE INVENTION 
       [0001]    This disclosure relates to track rollers for undercarriage bogies and, more particularly, to rigidly mounted track rollers. 
       BACKGROUND OF THE INVENTION 
       [0002]    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. 6 ). This practice, when extended to track rollers 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 
       [0003]    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 
         [0004]      FIG. 1  is an illustration of a vehicle that may make use of the invention; 
           [0005]      FIG. 2  is a side view of a frame and a portion of an undercarriage making use of the invention; 
           [0006]      FIG. 3  is a side view of a portion of the undercarriage that is not rotated with respect to the frame; 
           [0007]      FIG. 4  is a side view of the portion of the undercarriage of  FIG. 3  that is rotated with respect to the frame; 
           [0008]      FIG. 5  is a side view of the undercarriage; and 
           [0009]      FIG. 6  is a side view of a prior art undercarriage as disclosed in U.S. Pat. No. 7,025,429. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0010]      FIG. 1  is an illustration of a work vehicle in which may the invention may be utilized. The dozer  10  illustrated, includes a cab  20 , a body  30 , a main frame  40 , and a track frame assembly  100 . 
         [0011]      FIG. 2  illustrates a side view of a portion of the track frame assembly  100  as well as a portion of the main frame  40  and a rear sprocket drive  50  rigidly attached to the main frame  40  via a gearbox (not shown). As illustrated, the undercarriage  100  may include: 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  may be 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 connectors  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  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  is rotationally attached to the track frame  200  at fixed roller rotational axis  301  where the fixed roller rotational axis  301  is rigidly located with respect to the track frame  200 . As shown in  FIG. 5 , the undercarriage  100  also includes a track  101 . Note that only one track frame assembly  200  is illustrated in the Figures as the track frame  200  on the other side of the vehicle  10  may be an identical reflection of the illustrated track frame  200 . 
         [0012]    As illustrated in  FIGS. 2 ,  3  and  4 , the track frame  200  and the main frame  40  may be pivotally connected 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  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 frames  200  and may limit the angular range of rotation for each track frame  200  about the pivot shaft  201  to a maximum angular range of, for example, ±3°. 
         [0013]    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  110  to bend and conform to the contours of the ground. 
         [0014]    As illustrated in  FIG. 2 , the fixed roller  300  may not flex, with respect to the track frame  200 , to accommodate the contours of the ground as it may have an axis  301  that is rigidly fixed with respect to the track frame  200 . Additionally, the fixed roller  300  may be placed as close as practicable to the drive sprocket  50 . The proximity of the fixed roller  300  to the drive sprocket  50  may allow the fixed roller  300  to prevent 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  may also reduce the amount of weight and shock loading borne by the drive sprocket  50  because it may be able to bear a substantial portion of any load in that location due to its proximity to the drive sprocket  50 . As illustrated in  FIG. 2 , an axis of the pivot shaft  201  and the drive sprocket rotational axis  51  may be placed such that they are approximately equidistant from the ground, i.e., Y1≈Y2. 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. 
         [0015]      FIG. 4  illustrates the track frame at a maximum angular position of 3° with respect to the main frame, i.e., 3° in a direction that reduces the distance between an outer radius R 1  of the fixed roller  300  and an 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 minimum distance X min , as shown in  FIG. 4 , between R 1  and R 2  at the maximum angular position illustrated for non-interference between the fixed roller  300  and the drive sprocket  50  may be in a range of 3 to 6 centimeters. Thus, the track frame  200 , the main frame  40  and the drive sprocket  50  may be designed such that the distance between D 1  and D 2  is between 3 and 6 centimeters at the maximum angular position of 3°. Such a design may result in the minimum practicable distance between R 1  and R 2  at an angular position of 0°. 
         [0016]    As described above and illustrated in  FIG. 3 , the fixed roller rotational axis  301  may move with respect to the drive sprocket rotational axis  51  whenever the track frame  200  rotates with respect to the main frame  40  about pivot shaft  201 . As described earlier rotational movement between the track frame  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  110  is at its maximum (e.g., 3°) in a direction that reduces the distance between the fixed roller  300  and the drive sprocket  50 . In this exemplary embodiment, the minimum practical distance D min  between the outer diameter D 1  of the fixed roller  300  and the outer diameter D 2  of the drive sprocket  50  may be between 3 and 6 centimeters when the relative angle between the main frame  40  and the track frame  200  is at its maximum of 3°. 
         [0017]    Thus, assuming that the relative angle between the track frame  200  and the main frame  40  is approximately 0° at angle C of  FIG. 4 , the minimum practical distance D min  in  FIG. 4  may equal (a2+b2−(2ab)×Cos (C−3°)) 1/2 −(D1+D2)/2. All undetermined angles and lengths may be determined using the law of sines and/or the law of cosines. Please note that the minimum practical distance for configurations other than this exemplary embodiment may be at any range greater that includes values greater than 0 centimeters at a maximum angle of any value greater or less than 0°. 
         [0018]    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.