Patent Publication Number: US-8992157-B2

Title: Hydraulic cylinder with guide bushing for a sliding dipper handle of a power shovel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a U.S. national stage of and claims priority to and the benefit of International Application No. PCT/US2009/045422, entitled “Hydraulic Cylinder With Guide Bushing For A Sliding Dipper Handle Of A Power Shovel,” filed May 28, 2009, which is incorporated herein by reference in its entirety. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to power shovels, and more particularly to hydraulic mechanisms for operating a sliding dipper handle of the mining shovel. 
     2. Description of the Related Art 
     A typical mining power shovel includes a turntable mounted on a crawler truck, and supporting an A-frame and a cab. A boom, extending from the turntable, has an upper end supported by the A-frame and pivotally supporting a dipper handle that pivots in a vertical plane. A dipper fixed to a distal end of the dipper handle is raised and lowered by a hoist cable which extends over a sheave at the top of the boom and down to a padlock on the dipper. The hoist cable provides for the vertical, raising and lowering, movement of the dipper. A crowd assembly extends and retracts the dipper handle to provide the horizontal component, or crowd, of the dipper&#39;s movement. 
     Many different crowd assemblies have been developed over the years. Rack and pinion crowd assemblies include a rack fixed to the dipper handle which engages a rotatably driven pinion, or gear, mounted in the boom. Rope crowd assemblies include metal ropes that are wound and unwound from a crowd drum to extend and retract the dipper handle. 
     Also known in the art are hydraulic crowd assemblies, which utilize a large double-acting hydraulic actuator. U.S. Pat. No. 3,425,574 discloses a hydraulic crowd assembly that has a saddle block comprising a tubular support frame pivotally coupled by a yoke to the boom. A round tubular dipper handle, attached to the dipper, slides into and out of the support frame as the dipper moves with respect to the boom. That sliding motion is driven by a double acting hydraulic actuator comprising a cylinder within which a piston moves in response to pressurized hydraulic fluid being fed into the cylinder. A piston rod, connected to the piston, projects outward through an aperture at one end of the cylinder. The other end of the cylinder is attached to an extremity of the support frame that is remote from the saddle block and the exterior end of the piston rod is connected to a section of the dipper handle that is remote from the support frame. Thus the hydraulic actuator is supported at one end by connection of the cylinder to the support frame and at the other end by attachment of the piston rod to the dipper handle. Except at those ends, there are no supports between the either the hydraulic actuator and either the dipper handle or the saddle block. 
     Because hydraulic actuator of the dipper handle is very long, especially when the piston rod is extended significantly from the cylinder, and because the crowd assembly and its hydraulic actuator often extend substantially horizontal, the combination of the cylinder and piston rod can deflect or sag due to gravity. As a result, the rod frequently passes off center through the aperture in the cylinder, resulting in a smaller gap in the cylinder aperture above the rod than beneath the rod. In fact, the upper part of the piston rod can contact the cylinder, thereby scoring the surfaces sliding on each other. Over time, this deflection and the piston rod scoring can damage the aperture seal between the piston rod and the cylinder, resulting in leakage of hydraulic oil. 
     SUMMARY OF THE INVENTION 
     A crowd assembly includes a saddle block adapted for pivotal connection to a boom and for supporting a tubular dipper handle in a manner that allows the dipper handle to slide relative to the saddle block. 
     A hydraulic actuator has a cylinder and a piston rod that is extendable from one end of the cylinder. Either the cylinder or the piston rod is fixed to the dipper handle and the other one of the cylinder and the piston rod is stationary relative to the saddle block. The cylinder and the piston rod are received within the dipper handle, thereby enabling the dipper handle to slide longitudinally over the cylinder. 
     A guide bushing is affixed to the cylinder adjacent the one end and slideably engages an interior surface of the dipper handle. Thus the guide bushing supports that one end of the cylinder and maintains a position of the cylinder relative to the dipper handle as that latter component slides over the cylinder. The guide bushing prevents the hydraulic actuator from deflecting or sagging within the dipper handle as the piston rod is extended from the cylinder. 
     That support also maintains the piston rod substantially centered in an aperture of the cylinder thereby minimizing a likelihood of the piston rod contacting a wall of that aperture and enhancing the ability of a seal in that aperture to resist pressure of the fluid within the cylinder. 
    
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
         FIG. 1  is a side elevational view of a power shovel that utilizes a crowd assembly incorporating the present invention; 
         FIG. 2  is a side elevational view, partially in section, of the dipper handle and saddle block of the power shovel of  FIG. 1 ; 
         FIG. 3  is a longitudinal cross sectional view through the yoke of the saddle block showing a portion of the dipper handle therein; and 
         FIG. 4  is a longitudinal cross sectional view through a head end of the hydraulic cylinder with a guide bushing attached thereto. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a mining power shovel  10  includes a turntable  12  mounted on a crawler truck  14 , and supporting an A-frame  16  and a cab  18 . The cab  18  houses a power unit, control equipment, and the operator. The control equipment includes an electrical control system that operates the power shovel components in response to inputs from the operator and automatic devices, such as limit switches, pressure switches, and temperature switches, and the like. The operator can provide inputs from within the cab  18  through manually operable devices, such as a joystick, lever, foot pedals, rocker switches, computer keyboard, and touch pads, for example. 
     The A-frame  16  supports a top end  22  of a boom  24  and a bottom end  26  of the boom is supported by the turntable  12 . With additional reference to  FIG. 2 , a dipper  28  is mounted on the front end  29  of crowd assembly  30  that comprises a dipper handle  32 , a saddle block  34  and a double acting hydraulic actuator  50 . The dipper handle  32  is mounted at one end to the dipper  28  and is slideably supported in the saddle block  34  pivotally attached to the boom  24 . The saddle block  34  includes a yoke  36  and a tubular support frame  38  that projects rearwardly from the yoke and encloses the rear end of the dipper handle  32 . The saddle block yoke  36  is pivotally mounted to the boom  24 , so as to rotate in a vertical plane. A hoist cable  40  extends upward from a powered hoist drum (not visible) within the cab  18 , over a sheave  44  at the top end  22  of the boom  24  and down to a padlock  46  on the dipper  28 . The hoist cable  40  provides for the vertical, raising and lowering, movement of the dipper  28 . 
     The double acting hydraulic actuator  50  of the crowd assembly  30  includes a cylinder  52  and an extendible piston rod  54  that are enclosed in the support frame  38  and the dipper handle  32 . The hydraulic actuator  50  provides the horizontal component, or crowd, of the dipper&#39;s movement. In the embodiment disclosed herein, the cylinder  52  is fixed relative to the saddle block  34 , and the piston rod  54  is fixed relative to the dipper handle  32 . As a result, extension of the piston rod  54  from a retracted position in the cylinder  52  urges the dipper handle  32  telescopically from the support frame  38 . Conversely, retraction of the piston rod  54  into the cylinder  52  urges the dipper handle  32  from the extended position toward the retracted position. Of course, the cylinder  52  can be fixed relative to the dipper handle  32 , and the piston rod  54  can be fixed relative to the saddle block  34  without departing from the scope of the invention. 
     The double-acting hydraulic actuator  50 , shown in greater detail in  FIGS. 2 and 3 , includes the hollow cylinder  52  having a tubular shell  56 , a closed end  58 , and opposite open end that is closed by a head  60  welded to the shell. An inner end  62  of the piston rod  54  extends through an aperture  69  in the cylinder head  60  into the tubular shell  56 . A piston  64 , fixed to the inner end  62  of the piston rod  54 , contacts the interior surface of the cylinder shell  56 , thereby defining a cap or bottom end chamber  66  and a rod chamber  68 , each having a separate hydraulic fluid port (not shown). By supplying pressurized fluid to one port and draining fluid from the other port, the piston  64  is driven in one of two directions within the cylinder  52 , as is well known. That motion of the piston in one direction extends the piston rod  54  from the cylinder  52 , while the motion in the opposite direction retracts the piston rod into the cylinder. U.S. Pat. No. 7,174,826 describes a hydraulic system for operating the double-acting hydraulic actuator  50  in this manner. 
     Because the remote end of the piston rod  54  from the cylinder  52  is fixed to the interior of the dipper handle  32 , as the piston rod extends and retracts with respect to the cylinder  52 , the dipper handle also extends from and retracts into the support frame  38 . Because the dipper handle is tubular, that motion with respect to the support frame also causes the dipper handle  32  to slide longitudinally over the head  60  of the cylinder  52 , as specifically shown in  FIG. 3 . 
     The hydraulic actuator  50  is supported at its opposite ends, as was the case with previous crowd assemblies. In such previous crowd assemblies, however, the interior surface of the dipper handle was spaced from and did not contact the exterior of the cylinder. Therefore, when the piston rod was extended significantly from the cylinder, the combination of those components tended to deflect or sag due to gravity and other forces when the horizontal crowd assembly was substantially horizontal. 
     The present structure prevents that deflection or sagging by placing a guide bushing  70  around the exterior of the cylinder head  60 , as shown in  FIGS. 3 and 4 . The cylinder head  60  is formed by three components  71 ,  72 , and  73  that fit against one another and are held together by a plurality of sets of bolts  74  and nuts  76 , only two sets being visible in  FIG. 4 . A tubular body  71  of the cylinder head  60  is secured to the end of the cylinder shell  56 , such as by welding for example, to provide a fluid tight seal. An annular seal carrier  72  is against the body  71  and has a plurality of grooves  77  extending circumferentially on its interior surface. A separate sealing ring  78  is received within each of those grooves  77  to seal a small gap between the cylinder head  60  and the piston rod  54  and prevent the pressurized hydraulic fluid from leaking out of the cylinder  52 . An annular retainer plate  73  completes the cylinder head  60  and has a surface against which the nuts  76  engage when threaded onto the cylinder head bolts  74 . The seal carrier  72  is against the head body  71  and the retainer plate  73  is against the seal retainer. Gaskets may be provided between the head body  71  and the seal carrier  72  and between the seal retainer and the retainer plate  73 , nevertheless the head body, seal retainer, and the retainer ring in that case are still considered as being against each other. 
     The guide bushing  70  has a tubular shape and extends around the outer circumferential surface of the cylinder head body  71 . The guide bushing  70  has an inwardly projecting flange  80  that extends into an annular groove  82  in the exterior surface of the cylinder head body  71 . The guide bushing abuts a wall of that groove  82  thereby limiting the extent to which the guide bushing  70  is able to slide longitudinally over the outer surface of the body  71 , i.e., in the leftward direction in the orientation shown in  FIG. 4 . An annular bushing retainer  84  also is received within the groove  82  abutting and securing the guide bushing  70  on the body  71 . During assembly of the cylinder head  60 , the guide bushing  70  and the bushing retainer  84  are initially placed around the body  71 . Then the seal carrier  72  is inserted onto the bolts  74  and positioned against the body  71 . The seal carrier  72  has an outer diameter that is larger than the diameter of the groove  82  in the body, thereby captivating the bushing retainer  84  and preventing rightward movement of the guide bushing  70  in the illustrated orientation. The retainer plate  73  then is inserted onto the bolts  74  and secured in place by the nuts  76 . 
     The guide bushing  70  may be fabricated of a self-lubricating, fabric reinforced resin material, such as that marketed under the brand name ORKOT 361 by Trelleborg AB of Trelleborg, Sweden. The material of this guide bushing  70  contains a lubricant. Nevertheless, the guide bushing  70  may be made of other suitable materials, for example, various plastics, such as nylon or polytetrafluoroethylene, or metal, such as bronze or brass. Regardless of the material used, the guide bushing  70  may or may not be provided with self lubricating components. 
     Referring again to  FIG. 3 , when the crowd assembly  30  is put together, the outer curved surface of the guide bushing  70  contacts the interior surface of the dipper handle  32 . This supports the cylinder head  60  within the dipper handle and prevents the cylinder  52  and piston rod  54  from sagging or deflecting due to gravity and other forces acting on the crowd assembly. That support also maintains the piston rod  54  centered within the aperture  69  of the cylinder head  60  so that a substantially equal gap occurs between the interior diameter of the cylinder head and the outer diameter of the piston rod. This enables a very small gap to be formed which can be tightly sealed by the sealing rings  78 . In prior crowd assemblies in which the cylinder head was not supported by a guide bushing  70 , a relatively large gap occurred below the piston rod which required a much larger seal and lower operating hydraulic system pressures to be utilized. With a smaller gap in the present structure, a greater operating pressure can be utilized within the rod chamber  68  without the seal rings  78  failing. In addition, centering the piston rod  54  within the aperture  69  also minimizes the possibility of a direct metal to metal contact between the components of the cylinder head  60  and the piston rod  54 . This prevents the wear and galling of those sliding surfaces which could also produce seal failure and the consequential failure of the overall cylinder. 
     The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.