Abstract:
An eccentric shaft assembly for a vibratory roller utilizes a cylindrical tubular shaft that considerably reduces the weight of the assembly, decreases substantially oscillatory shaft deflection during rotation and thereby improves bearing and seal life. The eccentric weights are mounted on the interior of the tubular shaft, thereby simplifying manufacture and providing a smoother operation.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention pertains to vibratory rollers for soil and backfill compaction and, more particularly, to an improved shaft assembly for a vibratory roller.  
         [0002]     Vibratory rollers are well known in the utility and road construction industries for compacting backfill and other fill materials. Typically, such rollers include a large cylindrical roller drum attached to a piece of off-road equipment for movement over the surface to be compacted. A vibratory exciter shaft is mounted axially inside the drum, journaled to rotate independently of the drum and driven at high speed to impart vibratory motion to the drum to facilitate compaction. A vibratory roller may also be mounted with a scraper blade, such as shown in the apparatus of U.S. Pat. No. 5,062,228.  
         [0003]     As shown in the above-identified patent and typical of the prior art, the exciter shaft comprises a solid steel shaft to opposite ends of which are welded aligned eccentric weights. It is also known to fasten the eccentric weights to the solid shaft with bolted connections. The opposite ends of the solid shaft are journaled in the end walls of the drum utilizing a bearing and seal arrangement. It has been found, however, that a solid steel eccentric shaft, having a typical diameter of about 3 inches (about 75 mm), is subject to excessive deflection at high speed rotation in the unsupported center of the shaft. This deflection is transmitted to the bearings and end seals, resulting in excessive misalignment, overheating, leakage and eventual failure of both the seals and bearings. Also, bolted connections are less reliable and more susceptible to failure then welds.  
         [0004]     In accordance with the present invention, the prior art solid steel shaft is replaced by a hollow shaft of improved stiffness, yet lower weight, with an improved mounting for the eccentric weights and a lubrication system that is more effective and efficient.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention is directed to a shaft assembly for a vibratory roller of the type having a roller drum enclosed by annular end walls on opposite axial ends of the drum, the shaft assembly comprising a cylindrical tubular shaft, eccentric weights mounted on the interior wall of the tubular shaft and equally distributed axially therewithin, a pair of shaft ends that enclose the opposite axial ends of the tubular shaft, each shaft end including a reduced diameter stub shaft that carries a bearing and seal journaled in the drum end wall for rotation relative thereto.  
         [0006]     In the preferred embodiment, a tubular shell encloses the tubular shaft and is operatively attached at opposite ends to the end walls of the roller drum for rotation therewith. The tubular shell and the tubular shaft define a sealed annular oil chamber. In the preferred construction, each drum end wall has mounted centrally therein an end cap that surrounds one of the stub shafts and provides the journaled mounting for the bearing and seal. The end cap includes a cylindrical outer surface portion that is adapted to be received in a counterboard end of the tubular shell for attachment thereto. One of the stub shafts is provided with a drive connection for transmitting driving rotation to the tubular shaft.  
         [0007]     In the preferred embodiment, the eccentric weights comprise a solid semi-cylindrical weight on each end of the interior of the tubular shaft adjacent the shaft ends, the weights positioned in axial alignment within the tubular shaft. Each of the eccentric weights has a diameter equal to the ID of the tubular shaft. Preferably, oil distribution elements are attached to the OD of the tubular shaft and oriented with respect to the direction of shaft rotation to direct oil in the oil chamber axially toward the bearings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The drawings illustrate the best mode presently contemplated of carrying out the invention.  
         [0009]     In the drawings:  
         [0010]      FIG. 1  is a perspective view, partly exploded and partly in section, showing the shaft assembly of the present invention.  
         [0011]      FIG. 2  is an enlarged sectional view through the drum of a vibratory roller showing the mounting of the shaft assembly of the present invention.  
         [0012]      FIG. 3  is a sectional view taken on line  3 - 3  of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]     Referring to  FIGS. 1 and 2 , a roller drum  10  for a vibratory roller has a cylindrical outer wall  11  enclosed at opposite ends by annular end walls  12 . An arrangement (not shown) for mounting the roller drum  10  to a carrying vehicle, such as a tractor, is connected to the end walls  12 . Such a mounting arrangement is shown, for example, in above-identified U.S. Pat. No. 5,062,228 which is incorporated by reference herein.  
         [0014]     A vibratory shaft assembly  13  of the present invention is mounted on the axis of the drum  10  between the end walls  12 . The shaft assembly  13  includes a cylindrical tubular shaft  14  which, in one embodiment, is made from a steel tube having an OD of 6 inches (about 150 mm) and a wall thickness of 0.25 inch (about 6 mm). This thin wall tubular shaft  14  replaces the solid steel shaft used in the prior art, as shown in the above identified patent.  
         [0015]     The opposite ends of the tubular shaft  14  are closed with a pair of shaft ends  15  which are machined from circular bar stock. The shaft ends  15  are welded to the ends of the tubular shaft  14 , but prior to attachment, a semi-cylindrical eccentric weight  16  is welded to the ID of the tubular shaft at each end. Each eccentric weight  16  has a diameter that corresponds to the ID of the tubular shaft  14  and is positioned to lie immediately adjacent the inside face  17  of a shaft end  15 . Each shaft end  15  includes a reduced diameter stub shaft  18  on which is mounted the inner race of a bearing  20  and the inner surface of a rotary seal  21 .  
         [0016]     The tubular shaft  14  is enclosed by a tubular shell  22  that is welded at opposite axial ends around the periphery of circular openings  23  in the drum end walls  12 . The tubular shaft  14 , including the shaft end  15 , bearing  20  and seal  21 , is mounted for rotation within the tubular shell  22  by an end cap  24 . The mounting assembly to be described is essentially identical for both ends of the shaft assembly  13 . Thus, each end cap  24  has a cylindrical outer surface  25  by which the end cap is received in a counterbore  26  in the end of the tubular shell  22 . An O-ring seal  27  seats in a groove in the cylindrical outer surface  25  to prevent leakage of oil past the shell  22  and end cap  24  interface. Each end cap  24  also includes an outer mounting flange  28  by which the end cap is attached to the drum end wall  12  with a circular pattern of mounting bolts  30 . The ID of the end cap  24  is provided with an inside counterbore  31  which receives the outer race of the bearing  20 . The bearing is held in place with a retaining ring  32 . The end cap also has an interior flange  33  that receives the outer face of the seal  21  which, in turn, is enclosed and held on the surface of the stub shaft  18  by a breather cap  34 . The breather cap is used only on one axial end of shaft assembly, the end cap  24  at the opposite end being tapped for attachment of the drive pulley (not shown) or the like used to impart rotary motion to the tubular shaft  14 .  
         [0017]     Thus, the cylindrical tubular shaft  14  and eccentric weights  16  mounted therein are journaled by the shaft ends  15  for rotation inside and relative to the tubular shell  22 . The thin annular space  35  between the OD of the tubular shaft  14  and the ID of the tubular shell  22  is partially filled with oil to provide lubrication for the bearings  20 . The main seals  21  and O-ring seals  27  retain the oil within the annular space  35 . Oil distribution elements  36  are welded to the OD of the tubular shaft  14  to assist in lubricating the bearings  20 . The annular space  35  is filled with oil only to a depth of about ⅓ the diameter of the tubular shell  22 . The oil distribution elements  36  comprise short lengths of bar stock or key stock and are oriented with respect to the direction of shaft rotation to direct oil in the annular space  35  toward the bearings  20 .  
         [0018]     In addition to the preferred embodiment described above, the tubular shaft  14  could be mounted in a manner in which it extends through the end walls  12  of the roller drum  10  and journaled for rotation relative to the drum on external bearings. The external bearings could be attached, for example, to the plate on the carrying vehicle which also mounts the drum  10  for rotation. Such a plate or “spider” be shown as item 16 in U.S. Pat. No 5,062,228. With bearings mounted externally of the drum  10 , the tubular shell  22  and the end caps  24  of the preferred embodiment may also be eliminated because an oil chamber  4  internal lubrication of the bearings would no longer be needed. Nevertheless, a fully functional alternative construction utilizing the hollow cylindrical shaft  14  and internally mounted eccentric weights  16  may still be used. With respect to the eccentric weights, instead of the two semi-cylindrical weights  16  welded to the interior of the tubular shaft  14 , alternate constructions, such as a single piece of bar stock welded to the inner wall of the shaft, could also be used.  
         [0019]     By replacing the solid steel shaft of the prior art with the tubular shaft  14  of the present invention, shaft deflection has been reduced considerably and, as a result seal movement and bearing misalignment are also reduced. In addition, the mounting of the eccentric weights  16  inside the tubular shaft  14  (rather than on the OD of the solid shaft of the prior art) minimizes the disturbance of oil in the oil chamber  35 , thereby reducing foaming and maintaining lower operating temperatures in the oil. The vibratory shaft assembly  13  of the present invention provides a marked improvement in operation, a lighter weight assembly, and substantially improved bearing and seal life.