Abstract:
A crawler assembly including a crawler frame member having a first crawler extension and a second crawler extension and an idler wheel disposed therebetween. The idler wheel defines a bore therethrough. The crawler assembly includes a shaft that extends through the bore. The shaft is fixed relative to the wheel by a tapered interference fit and rotatable relative to the first and second crawler extensions. A first side of the shaft is received by the first extension and has at least one journal bushing disposed therebetween. A second side of the shaft is received by the second extension and has a least one journal bushing disposed. A removable endcap is secured to each of the first and second sides of the shaft. A thrust surface is created at an interface between the endcaps and the journal bushings.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/551,343, filed Oct. 25, 2011, the entire contents of which is incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a mining shovel, and in particular to an idler wheel assembly. 
         [0003]    Front idler wheel assemblies are used in conjunction with machines, such as, among other applications, mining shovels, which utilize a straddle mount axle shaft support where the axle shaft is intended to rotate with the idler wheel. The current front idler wheel and idler axle shaft configuration utilizes a splined joint between the shaft and the wheel. The spline connection provides a torsional constraint between the two; however, the spline connection does not constrain the wheel from sliding axially from side to side across the splines. Side to side motion across the splines results in high wear between the components of the front idler wheel assembly. Furthermore, splined components found in the current idler wheel configurations are expensive to manufacture. 
       SUMMARY 
       [0004]    In one embodiment, the invention provides a crawler assembly including a crawler frame member having an idler wall disposed between a first crawler extension and a second crawler extension. The idler wheel defines a bore therethrough. The crawler assembly additionally includes a shaft extending through the bore. The shaft is fixed relative to the wheel by a tapered interference fit and rotatable relative to the first and second crawler extensions. A first side of the shaft is received by the first extension and has at least one journal bushing disposed therebetween. Similarly, a second side of the shaft is received by the second extension and has least one journal bushing disposed therebetween. A removable endcap is secured to each of the first and second sides of the shaft such that a thrust surface is created at an interface between the endcaps and the journal bushings. 
         [0005]    In another embodiment the invention provides a method of an idler wheel assembly including an idler wheel for attachment between a first extension and a second extension of a crawler frame. The wheel includes a bore that receives a shaft extending therethrough. A taper lock bushing is disposed between the shaft and the wheel such that the taper lock bushing creates an interference fit between shaft and the wheel. A first side of the shaft is received by the first extension and has at least one bushing disposed therebetween. Similarly, a second side of the shaft is received by the second extension and has a least one bushing disposed therebetween. A removable endcap is secured to each of the first and second sides of the shaft such that a thrust surface is created at an interface between the endcaps and the journal bushings. 
         [0006]    In another embodiment the invention provides an idler wheel assembly including an idler wheel for attachment between a first extension and a second extension of a crawler frame. The wheel includes a bore and is coupled to a wheel hub having a tapered inner diameter. A shaft extends through the bore of the wheel and the hub. A portion of the shaft includes a tapered outer diameter that is complimentary to the tapered inner diameter, whereby the interference fit is created therebetween to fix the shaft relative to the wheel. A first side of the shaft is received by the first extension and has at least one journal bushing disposed therebetween. A second side of the shaft is received by the second extension and has a least one journal bushing disposed therebetween. A removable endcap is secured to each of the first and second sides of the shaft such that a thrust surface is created at an interface between the endcaps and the journal bushings. 
         [0007]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is perspective view of a mining shovel. 
           [0009]      FIG. 2  is perspective view of a front idler wheel assembly and a crawler frame of the mining shovel. 
           [0010]      FIG. 3  is a perspective view of a front idler wheel assembly according to one embodiment of the invention. 
           [0011]      FIG. 4  is a cross-sectional view of the front idler wheel assembly of  FIG. 3 , taken along line  4 - 4 . 
           [0012]      FIG. 5  illustrates a taper lock bushing shown in  FIG. 4 . 
           [0013]      FIG. 6  illustrates a lock mechanism of the taper lock bushing shown in  FIGS. 4-5 , taken along  6 - 6  of  FIG. 5 . 
           [0014]      FIG. 7  is a perspective view of a front idler wheel assembly according to another embodiment of the invention. 
           [0015]      FIG. 8  is a cross-sectional view of the front idler wheel assembly of  FIG. 7  taken along line  8 - 8 . 
       
    
    
       [0016]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
       DETAILED DESCRIPTION 
       [0017]      FIGS. 1 and 2  illustrate a mining shovel  10  including a main platform  14 , a lower frame  18 , and a crawler assembly  22 . The crawler assembly  22  includes, in part, a first crawler frame member  26  and a second crawler frame member  30 , and constitutes a framework that supports motion of the mining shovel  10 . The first and second crawler frame members  26 ,  30  each support a crawler track  50  on either side of the mining shovel  10 . Each of the crawler frame members  26 ,  30  includes a first extension  54  and a second extension  58 , each with a rectangular opening  62  having a shim plate  66  and a shaft guard  70  positioned therein. The crawler frame members  26 ,  30  each define a top of the crawler frame  38  and include a front idler wheel assembly  78 , carrier wheels  42 , and a rear driven crawler wheel  46 . Each front idler wheel assembly  78  includes a front idler wheel  34 , or a gear in some embodiments, positioned between the two extensions  54 ,  58  of the respective frame member  26 ,  30  and coupled to an idler axle  74  shaft for rotation therewith. The axle shaft  74  extends through a bore (not shown) in a center of the idler wheel  34  and through a bore (not shown) in each of the extensions  54 ,  58  of the respective crawler frame member  26 ,  30 . 
         [0018]      FIGS. 3-6  illustrate one of the front idler wheel assemblies  78  according to an embodiment of the invention. The front idler wheel assembly  78  includes the front idler wheel  34  locked to the idler axle shaft  74 , which extends through a central bore (not shown) in the front idler wheel  34 . In the illustrated embodiment, the front idler wheel  34  includes a hub portion, although in further embodiments the wheel  34  may be a single piece. In the illustrated embodiment, a diameter  84  of the idler axle shaft  74  is smaller than a diameter  86  of the central bore of the front idler wheel  34 , which creates a small gap (not shown) therebetween during assembly. A taper lock bushing  90  is positioned within the gap. Due to extremely high radial loads applied through front idler wheel  34  during travel by the shovel  10  and as a result of the size of the components of the front idler wheel  34  and the idler axle shaft  74 , a pair of taper lock bushings  90  ( FIG. 4 ) are included in each front idler wheel assembly  78 . One bushing  90  is installed from either side of the idler wheel  34 . Access to the taper lock bushings  90  during assembly and disassembly is provided through the rectangular openings  62  of the first side  54  and the second side  58  of crawler frame members  26 ,  30 . Additionally, each of the bushings  90  is covered by a contamination cap  88 , which keeps debris (i.e., water, dust, dirt) from the bushings  90 . The taper lock bushing  90  creates an interference fit, thereby locking the front idler wheel  34  to the idler axle shaft  74 . The interference fit provides a rigid connection that constrains the front idler wheel  34  and the idler axle shaft  74  axially, radially, and torsionally. Thus, the interference fit restricts the motion of the wheel  34  preventing high wear in the front idler wheel assembly  78 . 
         [0019]    As is shown in  FIGS. 5 and 6 , the taper lock bushing  90  includes a first inner member  94 , a second inner member  96 , and an outer member  100 . The inner members  94 ,  96  have tapered outer surfaces  92  that are complimentary to and interface tapered inner surfaces  102  of the outer member  100  of the taper lock bushing  90 . Additionally, the taper lock bushing  90  includes two types of axially extending holes: full-length holes  118  and half-length holes  120 . The full-length holes  118  extend a length of the bushing  90 . Holes  118  are defined by a through-hole portion  118   a,  which extends through the first inner member  94  of the bushing  90 , and a threaded hole portion  118   b,  which extends through the second inner member  96  of the bushing  90 . Holes  120  are threaded and extend through the first inner member  94  of the bushing  90 ; therefore, the holes  120  extend approximately half way through the bushing  90  and do not have a portion defined in the second inner member  96 . In the illustrated embodiment, there are a pair of holes  118  for every one hole  120 , with one hole  120  positioned between adjacent pairs of holes  118 . The full-length holes  118  are assembly holes while the half-length holes  120  are disassembly holes. 
         [0020]    During assembly of the front idler wheel assembly  78 , fasteners  104  (e.g., screws) are used to create an interference fit between the front idler wheel  34  and the idler axle shaft  74 . The interference fit is accomplished by tightening the fasteners  104 . The fastener  104  is inserted into the through-hole portion  118   a  of the respective hole  118  and screwed into the threaded portion  118   b  of the hole  118 . As the fastener is screwed into the threaded portion  118   b,  the two members  94 ,  96  of the bushing  90  are pulled closer together. As the two members  94 ,  96  are brought closer together, the tapered outer surfaces  92  slide in relation to the tapered outer surfaces  102  of the outer member  100 , thereby pushing the outer member  100  radially outward and the inner members  94 ,  96  radially inward. As such, an outer diameter  108  of the bushing  90  radially expands, while an inner diameter  112  of the bushing  90  radially contracts. Expansion of the outer diameter  108  of the taper lock bushing  90  against the inner diameter  86  of the central bore of the front idler wheel  34  and simultaneous contraction of the inner diameter  112  of the taper lock bushing  90  against the idler axle shaft  74  creates the interference fit between the wheel  34  and the shaft  74 . The expansion and contraction of the lock bushing  90  also produces significant surface pressure between the front idler wheel  34  and the idler axle shaft  74 , thus locking them together and into position. 
         [0021]    During disassembly of the front idler wheel assembly  78 , the fasteners  104  may also be used to disassemble the taper lock bushing  90 . After all of the fasteners  104  are removed from the assembly holes  118 , some of the fasteners  104  are tightened into the other set of holes  120 . As the fasteners  104  are tightened into the half-length holes  120 , the fasteners  104  contact the second member  96 . Because that portion of the member  96  does not have a hole, tightening of the fastener  104  pushes the second member  96  away from the first member  94  so that the tapered outer surfaces  92  of the inner members  94 ,  96  slide in relation to the tapered outer surfaces  102  of the outer member  100 . This movement causes the outer member  100  to move radially inward and inner members  94 ,  96  to move radially outward. Therefore, the outer diameter  108  of the bushing  90  radially contracts while the inner diameter  112  of the bushing  90  radially expands. Thus, the bushings  90  are returned to their loose fit starting positions. While the front idler wheel components are assembled, the unlocking holes  120 , which are threaded, are used to couple the contamination cap  88  to the taper lock bushing  90 . Fasteners  110  occupy the holes  120 , thereby coupling the contamination cap  88  to the bushings  90 . The contamination cap  88  protects the bushings  90  from debris that fills the opened unlocking holes  120 , cause the tapered surfaces  92  and  102  to rust tight, and inhibit loosening and removal of the bushings  90 . 
         [0022]    The extensions  54 ,  58 , of the crawler frame members  26 ,  30  lend lateral support to both sides of the front idler wheel  34  because the idler axle shaft  74  extends through the central bore (not shown) of the front idler wheel  34  and through a bore (not shown) in each of the two extensions  54 ,  58 . Referring to  FIG. 4 , the axle shaft  74  is received by and rotates relative to two journal bushings  124  positioned on opposite sides of the idler wheel  34 . Each of the bushings  124  is fixed to a bushing block  128  that is attached to the respective extension  54 ,  58  of the crawler frame members  26 ,  30 . Each of the bushing blocks  128  includes a recess  132  for lubrication lines to lubricate the journal bushings  124 . Fasteners  136 , or connectors, couple axle end caps  140  to the idler axle shaft  74  for rotation therewith, and the fasteners  136  extend through shims  144 . A thrust surface  146  is located at an interface between the journal bushings  124  and the axle end cap  140 . In the illustrated embodiment, the axle end caps  140  wear against the journal bushings  124  as a result of side thrust forces that are introduced to the front idler wheel  34  as the shovel  10  moves and pivots. As increased wear occurs on the journal bushings  124 , the axle end caps  140  are removed to replace the journal bushings  124  without disassembling the entire front idler wheel assembly  78 . Furthermore, the shims  144  in between the idler axle shaft  74  and the axle end caps  140  may be removed to reduce the gap between the journal bushings  124  and axial end caps  140 , as the journal bushings  124  wear away. 
         [0023]      FIGS. 7 and 8  illustrate a front idler wheel assembly  278  according to another embodiment of the invention. The front idler wheel assembly  278  of  FIGS. 7 and 8  is similar to the front idler wheel assembly  78  of  FIGS. 3-6 ; therefore, like structure will be identified by like reference numbers plus “200” and only the differences will be discussed hereafter. 
         [0024]    The front idler wheel assembly  278  includes an idler axle shaft  274 , which extends through a central bore (not shown) of a wheel hub  348  coupled to a front idler wheel  234 . The wheel hub  348 , which is coupled (e.g., by welding) to an inner diameter  286  of the wheel  234 , fills a gap (not shown) between the front idler wheel  234  and the idler axle shaft  274 . Referring to  FIG. 8 , both the axle shaft  274  and the wheel hub  348  include a tapered portion,  352  and  356  respectively, of the diameter, which are complementary to each other. An angle of taper of the tapered portions  352  and  356  of both the idler axle shaft  274  and the wheel hub  348  is approximately 3.6°. However, in further embodiments, the angle of taper could be greater or less than 3.6°. 
         [0025]    During assembly, a substantial force is applied using an external device in the direction of arrow  360  to drive mating components, the front idler wheel  234  and the idler axle shaft  274 , axially together; thereby creating significant surface pressure. The surface pressure keeps the front idler wheel  234  and the idler axle shaft  274  fixed together after the force is removed and during operation of a mining shovel  10 . The tapered surfaces of the axle shaft  274  and the idler wheel hub  348  provide the interference fit therebetween, thereby providing a rigid connection to constrain the front idler wheel  234  and the idler axle shaft  274  axially, radially, and torsionally. The interference fit is accomplished by manufacturing both the axle shaft  274  and idler wheel  234  with a small degree of taper on the mating diameters. Thus, the interference fit restricts the relative motion of the wheel  234  and the idler axle shaft  274  preventing high wear in the front idler wheel assembly  278   
         [0026]    In a further embodiment, the front idler wheel assembly does not include a wheel hub and the inner diameter of the idler wheel is manufactured with a tapered surface. An interference fit is created between the front idler wheel and the tapered axle shaft by mating the tapered surfaces of the two components. 
         [0027]    Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described. 
         [0028]    Thus, the invention provides, among other things, a rigid connection between components of an idler wheel assembly thereby preventing sliding wear on joint surfaces by restricting movement of the idler wheel and rotating axle shaft radially, axially, and torsionally. Various features and advantages of the invention are set forth in the following claims.