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BACKGROUND OF THE INVENTION 
     The present invention pertains to a vibratory exciter unit that is adapted for interchangeable connection to a number of diverse vibratory tools and for vibration isolating connection to a tool carrier. 
     Many types of soil excavation, compaction and other construction activities utilize vibratory tools of various types to facilitate the particular activity. Such vibratory tools include compaction rollers, compaction plates, vibratory plows, asphalt cutters, concrete breakers and pile and sheet drivers and extractors. Such vibratory tools are often connected to the boom of an excavator or similar off-the-road vehicle such that the boom can be operated to place, maneuver, and apply downpressure to the tool during use. It is important to isolate the vibratory tool from the excavator boom and the machine that operates the boom. It is known in the art to provide elastomer isolators between the boom and the exciter unit, as shown for example in U.S. Pat. No. 5,244,306 which is incorporated by reference herein. 
     Because of the wide variety of vibratory tools that are made for attachment to an excavator or the like, special connectors and attaching arrangements are often needed to adapt a particular manufacturer&#39;s vibratory tool to the boom of an excavator made by a different manufacturer. The typical connection between an excavator boom and a vibratory tool includes a connecting link attached to the boom with two pivot pins, the link is also connected with vibration isolating mounts to the vibratory tool. Differences in boom sizes and connecting pin lengths and diameters require the manufacturers of many vibratory tools to stock a large number of parts to accommodate the connections. With respect to the vibratory tool itself, typically connected to the bottom of the connector mechanism, there is little or no interchangeability when changing from one vibratory tool to another. 
     Elastomer vibration isolators that operate in shear have long been used, but are not very effective and are subject to failure in high load applications. It is also known in the prior art to use elastomer vibration isolators of an annular construction that operate in compression. Both types may be made from material having a flexibility (durometer) that is a compromise between those applications best handled with softer elastomer materials and applications better handled with harder elastomer vibration isolators. For example, in compacting sand or more granular materials, high amplitude and lower load compaction is preferable, whereas in compacting clay and similar materials, high load, low amplitude vibrations are preferable. It has also been found that in using annular elastomer vibration isolators in high vertical load applications, the elastomer mounts are subject to unacceptably high compression forces as a result of being compressed past their design limits. This often results in destruction of the isolator by loss of the bond by which the isolator is attached to the metal parts to which it is bonded. This results in loss of isolation and the transfer of vibrations back to the boom and to the vehicle to which it is attached 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a vibratory exciter unit is adapted for interchangeable connection to a number of different types of vibratory tools and may be easily connected to tool carriers of varying sizes. The apparatus includes an exciter housing in which is mounted a rotary vibratory unit and a drive for imparting rotary motion to the vibratory unit. The housing has a pair of generally vertical, laterally spaced side plates that are interconnected by a housing top plate. An upper connector frame has a pair of generally vertical, laterally spaced side frame members that are interconnected by a bottom plate, the bottom plate overlying the exciter housing top plate. Primary vibration isolators provide connections between the housing side plates and the connector frame side members, and secondary vibration isolating means are positioned between the opposed surfaces of the housing top plate and the connector frame bottom plate. Downward vertical load imposed on the vibratory tool by the boom causes initial deflection of the primary vibration isolators. When the vertical load reaches a level approaching the maximum desired compression of the primary vibration isolators, the secondary vibration isolating means is engaged, preventing the primary isolators from becoming over-stressed and possible destruction thereof. 
     The apparatus also includes a common connection means for attaching a variety of selected tools to the exciter housing side plates. Further, the apparatus includes adjustable connectors for attaching upper edge portions of the side frame members to a variety of tool carriers having varying lateral widths. 
     In a preferred embodiment, each of the primary vibration isolators comprises an annular elastomeric member that is captured in a cylindrical boss extending inwardly from an interior face of the side frame member. A threaded connector extends through the side plate and the open interior of the elastomeric member to provide the vibration-isolated connection between the side plate and the side frame member. This connection is designed to be fail-safe so that the halves will not be able to separate if there is a failure in the isolators. 
     The apparatus also preferably includes a tertiary vibration isolating means that is positioned between the upper surface of the connector frame bottom plate and a lower surface of an extension plate that is supported by the threaded connector. The secondary and tertiary vibration isolating means comprise sheets of elastomeric material that has a large surface area to thickness ratio. 
     The sheet of elastomeric material comprising the second vibration isolating means is attached either to the housing top plate or to the connector frame bottom plate and, in a static no-vertical-load condition or loaded up to a predetermined amount is spaced from the other of said plates. Preferably, the sheet of elastomeric material for the secondary vibration isolating means is attached to the housing top plate and spaced from the connector frame bottom plate. The elastomeric material for the primary vibration isolators is selected to provide initial deflection under a downward vertical load imposed by the tool carrier and higher amplitude vibration caused by the exciter, and the elastomeric material for the secondary vibration isolating means is selected to minimize further deflection of the primary deflection isolators under a vertical downward load beyond a selected maximum and still isolate the lower amplitude vibration. 
     The sheet of elastomeric material comprising an optional tertiary vibration isolating means is attached either to a lower surface of an extension plate supported by the threaded connector or to the upper surface of the bottom plate of the connector frame and, in a static no-vertical-load condition, is spaced from the other of said plates. Preferably, the sheet of tertiary elastomeric material is attached to the extension plate and is spaced from the bottom plate. The elastomeric material for the primary vibration isolators is selected to provide initial deflection under upward vertical load imposed by the tool carrier and vibration amplitude, and the elastomeric material for the tertiary vibration isolating means is selected to prevent deflection of the primary vibration isolators under a vertical upward load beyond a selected maximum. 
     The tool carrier typically comprises the boom of an excavator which has a connection end with a lateral width less than the distance between the connector side frame members. The tool carrier typically utilizes a connecting pin to connect the boom end to the side frame members. In accordance with another aspect of the invention, the connectors comprise a bushing assembly that is attachable to the side frame members for receipt of the connecting pin and is adjustable axially to establish a width for a close clearance fit of the end of the boom. Most typically, the end of the boom includes a boom arm and a lift arm, each having a connecting pin, the bushing assembly further comprising a pair of axially aligned bushing assemblies for each of the boom arm and the lift arm with the bushings sized to receive the respective connecting pins for pivotal movement therein. Preferably, the bushing assembly includes a clamping ring device that is operative to position the opposed inner ends of each axially aligned bushing pair at the established width of the boom end. 
     The means for attaching a selected tool to the housing side plates comprises demountable fasteners attachable to the tool and to lower edge portions of the housing side plates with a common bolt hole pattern. 
     In the preferred embodiment of the invention, the rotary vibratory unit comprises a pair of counterrotating eccentric weights that are each attached to a shaft operatively connected to the drive unit. Each of the eccentric weights comprises a semicylindrical mass attached to the shaft to present exposed generally flat radial face portions. A semicylindrical thin-walled shroud is attached to each semicylindrical mass to enclose the flat face portions and to define with the semicylindrical mass a generally cylindrical shape. The cylindrical shape is preferably closed by generally planar end faces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the vibratory exciter apparatus of the present invention attached to the boom of a excavator and carrying an exemplary vibratory tool. 
         FIG. 2  is an exploded perspective view of the exciter housing and connector frame. 
         FIG. 3  is an end elevation view of the assembled housing and frame of  FIG. 2 . 
         FIG. 4  is a vertical sectional view taken on line  4 - 4  of  FIG. 3 . 
         FIG. 4A and 4B  are enlarged details taken on lines  4 A and  4 B, respectively, of  FIG. 4 . 
         FIG. 5  is an exploded perspective view of the upper connector frame showing the adjustable bushing assemblies for facilitating pinned connection to the boom of a tool carrier. 
         FIG. 6  is a vertical section through the bushing assembly of  FIG. 5  in its assembled condition. 
         FIG. 7  is a vertical sectional view through the exciter housing showing the exciter casing and shrouded arrangement for the eccentric weights used with the vibratory unit. 
         FIG. 8  is an exploded perspective view of a shaft-mounted eccentric weight and shroud. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows the vibratory exciter unit  10  of the present invention having mounted to the bottom a conventional compactor roll as an example of one of many different types of vibratory compaction or other vibratory earth-working tools that can be easily and demountably attached to the exciter unit  10 . The exciter unit  10  is connected at an upper region to the boom  12  of an excavator, the boom being typically used to move, position and provide a vertical load to the compactor roll  11  or other vibratory tool mounted to the exciter unit  10 . 
     Referring also to  FIG. 2 , the vibratory exciter unit  10  includes an exciter housing  13  having a generally U-shaped vertical cross section and comprising a housing top plate  14  that interconnects a pair of laterally spaced side plates  15 . The top plate  14  is upwardly convex and provides a partial enclosure for a vibratory mechanism  16  suspended from the underside of the plate  14 . The vibratory mechanism includes a pair of counterrotating eccentric weights  17  driven by a hydraulic motor  18  (see  FIGS. 4 and 7 ). Details of the construction and operation of a vibratory mechanism of this type are shown in U.S. Pat. No. 4,927,289 which is incorporated by reference herein. 
     The bottom edges of the housing side plates  15  is provided with a pattern of bolt holes  20  to receive connecting bolts  21  for demountable attachment of the plate compactor tool  11  or any of a number of diverse vibratory tools. 
     A connector frame  22  is positioned above and attached to the exciter housing  13 . The connector frame is also generally U-shaped in vertical section and includes a bottom plate  23  interconnecting a pair of laterally spaced side frame members  24 . The bottom plate  23  is also upwardly convex and, when the connector frame  22  is attached to the exciter housing  13  as will be described hereinafter, the bottom plate  23  overlies and is closely spaced from the upper surface of the top plate  14 , as best seen in  FIG. 4 . 
     The connector frame  22  fits between the side plates  15  of the exciter housing  13  and is connected thereto with bolts  25 , but isolated from the transmission of vibrations by primary vibration isolators  26  at each of the bolted connections. 
     More specifically, each side frame member  24  is provided with three cylindrical bosses  27 , each of which houses a primary vibration isolator  26 . Each isolator  26  is of an annular construction and is made from an elastomeric material, either natural or synthetic rubber and having a Shore A durometer of 50. Similar materials of other compressibilities may also be used. Each isolator  26  is bonded to an interior cylindrical sleeve  28  and is held with a tight press fit in a cylindrical boss  27  on the side frame member  24 . Thus, the connecting bolts  25  pass through mounting holes  30  in the side plates  15  and through the cylindrical sleeves  28  of the primary vibration isolators  26 , the bolts  25  being secured with appropriate nuts  31 . 
     A secondary vibration isolator  32  is positioned between the exciter housing top plate  14  and the connector frame bottom plate  23 . Referring particularly to  FIGS. 2 and 4 , the secondary isolator  32  comprises a sheet of elastomeric material which has a large surface area to thickness ratio. The secondary isolator  32  preferably is made from a fabric reinforced natural or synthetic elastomer and is attached to the upper surface of the housing top plate  14  using fastener strips  33  secured with machine screws  34  or other suitable fasteners. The isolator sheet  32  has a thickness of about ½ in. (about 13 mm) and may have a surface area of about 300 sq. in. (about 2,000 sq. cm.). In the static-at-rest position, with no additional vertical load applied to the apparatus, the upper surface of the secondary isolator sheet  32  is spaced from the undersurface of the connector frame bottom plate  23  by a small amount, approximately ⅛ in. (about 3 mm). See the space  29  shown in the enlarged detail of  FIG. 4A . 
     In use, as the vibratory tool, such as plate compactor  11 , is placed on the surface to be compacted by the boom  12 , a vertical downward load is exerted on the apparatus, the magnitude of the load depending on the material being compacted. The vibratory mechanism  16  imparts vibration to the exciter housing  13  and plate compactor  11 , but the vibrations are isolated from transmission to the connector frame  22  and backhoe boom  12  by the primary vibration isolators  26 . As a vertical downward load is imposed on the apparatus, the primary isolators  26  will be compressed and, as the load is increased, the bottom plate  23  of the connector frame will move vertically downward toward the upper surface of the secondary isolator sheet  32 . However, before the elastomeric material in the primary isolators  26  is compressed beyond a safe maximum amount, the connector frame bottom plate  23  comes into contact with the secondary isolator sheet  32 . The large surface area and somewhat higher hardness (e.g. 80 Shore A durometer) of the secondary isolator prevents compression of the primary vibration isolators beyond their failure thresholds. The secondary isolator  32  continues to provide vibration isolation and, importantly, prevents the connector frame  22  from bottoming out on the exciter housing  13 . As the vertical downward load exerted by the boom increases, the initial high amplitude vibrations imposed on the primary vibration isolators  26  decrease in amplitude and, when contact between the bottom plate  23  and the secondary isolator  32  occurs, the amplitude of the vibrations decreases significantly and are absorbed by the secondary isolator  32 . This transfer of vibrations from the primary to the secondary isolators prevents a breakdown of the elastomer material in the primary isolators  26  and/or bond between the primary isolator material and the interior cylindrical sleeves  28 . 
     The vibratory apparatus may also be operated in a manner in which the boom  12  imposes a lifting or vertical upward load on the unit, as for example when used as a piling or sheet extractor. In this mode, the primary vibration isolators  26  must also be protected against excessive compression and breakdown in a manner similar to operation under a vertical downward load. 
     Referring again to  FIGS. 2 and 4 , tertiary isolator means  35  are positioned between the upper surface of the connector frame bottom plate  23  and the bottom surface of an extension plate  36  which is carried by the bolts  25 . More specifically, an extension plate  36  is mounted between each axially aligned pair of bolts  25  extending through the two outermost primary isolators  26  in the end plates  24 . Each extension plate  36  includes a pair of opposite mounting rings  37  connected to opposite ends of a circular section rod  38  and to a pair of backing plates  40  that extend parallel to the rod  38  to form a rigid structure. The tertiary isolator  35  comprises a sheet of fabric reinforced elastomer similar to the secondary isolator  32 , but having a substantially smaller surface area and a reduced thickness, preferably about ¼ in. (about 6 mm). The tertiary isolator sheet  35  is wrapped around the lower surfaces of the rod  38  and the backing plates  40  and secured thereto with fastener strips  41  and suitable fasteners. The mounting rings  37  are placed on the ends of the bolts  25  and secured with nuts  31  as part of the process of attaching the side plates  15  to the side frame members  24 . In the static no-load condition, the lower surface of the tertiary isolator sheet  35  is spaced very slightly from upwardly concave edges  42  on the connector frame bottom plate  23 . The no-load spacing is preferably about 0.1 in. (about 2.5 mm). See the space  39  shown in the enlarged detail of  FIG. 4B . In a manner similar to operation under a vertical downward load, the primary vibration isolators  26  will compress and absorb vibrations when the boom imposes a lifting force on the apparatus. However, before the elastomer elements in the primary isolators are compressed beyond a selected maximum, the tertiary isolators  35  are engaged, limiting deflection of the primary vibration isolators, yet continuing to provide vibration isolation between the vibratory exciter housing and the boom  12  or other attached machine. 
     Referring to  FIG. 7 , the vibratory mechanism  16  includes a pair of counterrotating eccentric weights  17 , as identified above, each of which is mounted on one of a pair of spaced parallel shafts  43 . As shown in  FIG. 4 , a drive linkage  44  from hydraulic motor  18  is operatively connected to the shafts  43  to provide driving rotation to the shafts and weights  17 . Each of the eccentric weights comprises a semicylindrical mass having exposed generally flat radial face portions  45  on opposite sides of the shaft  43 . The assembly of both eccentric weights  17  and their respective shafts  43  are mounted in a small exciter casing  46  attached to the underside of the housing top plate  14 . In operation, the exciter casing  46  contains lubricating oil in which the eccentric weights  17  rotate. It has been found that the flat face portions  45  of the eccentric weights create a great amount of turbulence in the oil which, in turn, leads to excessively high temperatures. Excessively high temperatures can lead to shortened life of elastomeric isolation mounts, lubricants, seals and bearings with consequent higher maintenance costs. 
     To reduce the generation of high temperatures in the exciter casing  46 , each of the eccentric weights  17  has attached to it a semicylindrical thin-walled sheet metal shroud  47 . The shroud encloses the flat face portions  45 , thereby defining with the semicylindrical mass a generally cylindrical shape which is aerodynamically smoother around its entire outer surface. This shrouding of the eccentric weights has been found to lower the operating temperature of the exciter by as much as one-half. Each of the shrouds  47  includes flat end faces  48  which lie coplanar with the corresponding end faces  50  of the eccentric weight  17 . The end faces  50  of the weights, where they intersect the face portions  45 , are preferably provided with recesses  51  to accommodate the thickness of the shroud  47  so that the end faces  48  and  50  define a smooth coplanar circular end face. Each shroud  47  may be attached to its respective weight  17  with suitable machine screws  52 . 
     Referring now to  FIGS. 5 and 6  and again to  FIG. 1 , the boom  12  of the backhoe or other carrying vehicle typically includes a main boom arm  53  and a lift arm  54 . Each of the arms  53  and  54  is attached to the connector frame  22  between the side frame members  24  with a pivotal connection utilizing a pin  55 . However, booms  12  from different manufacturers often have varying widths and utilize connecting pins  55  of different diameters. With the ends of the boom arm  53  and lift arm  54  positioned between the connector frame side frame members  24 , connecting pins  55  are inserted through the ends of the arm  53  or  54  and through a pair of axially aligned bushings  56  mounted in the side frame members  24 . To accommodate variations in widths of the boom and lift arms  53  and  54 , of different manufacturers, each of the bushings  56  is adjustably mounted such that it can be moved in an axial direction so that the opposed inner ends of the bushing pair provide a close clearance fit for the ends of the boom arms  53  and  54 . 
     Each bushing assembly includes a bushing  56 , that is inserted through an oversize hole  57  in the side frame member  24 , the hole  57  having a peripheral lip  59  on the inner edge. The assembly also includes a large diameter compression ring  58  with a tapered ID, a smaller diameter compression ring  60  with a tapered OD, an annular mounting plate  61  and a plurality of mounting bolt assemblies  62 . The compression rings  58  and  60  are slid onto the bushing  56 , and the bushing and compression rings are inserted from the outside into hole  57 . The mounting plate  61  is then placed over the bushing on the outside of the frame member  24  and brought into contact therewith for insertion of the mounting bolt assemblies  62 . The inner face of the mounting plate  61  forces the large diameter compression ring into contact with the lip  59  and captures the assembly of compression rings  58  and  60  in the oversize hole  57  and on the OD of the bushing. The bushings  56  of each axially aligned pair are positioned to establish the selected distance between their opposed ends to provide the desired close clearance fit for the end of the boom  12  as described above. When the bushings have been properly positioned, mounting bolt assemblies  62  are tightened causing the mounting plate to bear against the outer edge of the smaller diameter compression ring  60 , forcing it into the compression ring  58  causing the rings  58  and  60  to clamp the bushing  56  securely in position. 
     The bushing assembly eliminates the need to stock bushings of various lengths to accommodate different boom widths. However, pin diameters often vary considerably from one boom manufacturer to another, requiring the stocking of bushings with varying IDs. Nevertheless, the ability to use bushings of a single length cuts dramatically the inventory of bushings.

Summary:
A vibratory exciter apparatus can be interchangeably connected to a variety of diverse vibratory compaction and other earth-working vibratory tools and includes a vibration-isolating connection link to tool carriers of varying sizes. A vibratory exciter housing is isolated from the connector link and from the carrying tool to which the link is attached by a primary elastomer isolator group which is, in turn, protected from damaging overload in a vertical downward direction by a secondary elastomeric isolator sheet and from damaging vertical load in an upward direction by a tertiary elastomeric isolator sheet. The connecting link utilizes adjustable bushing assemblies to accommodate dimensional differences from one boom manufacturer to another. The vibratory exciter unit includes heat-reducing shrouds for the rotary eccentric weights.