Abstract:
A torque transfer assembly ( 30   a,    30   b,    30   c ) is assembled with reinforced fasteners ( 44 ) so that it may withstand the shear forces created by torque loads. The reinforcement is provided by surrounding the portion of a fastener subjected to shear stress with a sleeve-like tube key ( 40 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/175,162, filed Jan. 7, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates generally to torque transfer assemblies and, more particularly, to a torque transfer assembly assembled with reinforced fasteners so that it can better withstand shear force.  
           [0003]    Torque transfer assemblies, i.e. sprocket assemblies, are used to transmit torque in a wide variety of applications, from bicycles to clocks to industrial sized augers. Some of these applications require very little torque to perform a given function, i.e. a wristwatch. Other applications may experience high torque, i.e. auger systems that are used to literally move tons of materials such as concrete, rock, or agricultural products.  
           [0004]    Many torque transfer assemblies are composed of disks, i.e. sprockets, spaced apart along a rotational axis. The disks are often held together with bolts that have their longitudinal axes aligned with the rotational axis. Thus, when one sprocket or disk is subjected to a load that is resisted by the connected sprockets or disks, the bolts experience shear forces. Such resistance can occur when a driving disk is trying to turn a shaft that is connected to a loaded disk, i.e. when a motor is driving an auger by means of a sprocket assembly.  
           [0005]    As an example, a typical prior-art sprocket assembly  10  is shown in FIG. 1. The weakest point of such an assembly is on the bolt threads  24  where the stub shaft  12  and sprocket  14  meet. The bolts  20  can experience shear failure at this point. The problem could be alleviated by using larger diameter bolts or bolts made of a higher strength material, or by increasing the bolt circle. However, these are undesirable solution because such bolts are significantly more expensive, and increasing the bolt circle would require a shaft that is bulkier, heavier, and more expensive. Thus, there remains a need for a fastener that will not readily experience shear failure due to high torque loads, and not significantly increase the cost or bulkiness of the torque transfer assembly.  
         SUMMARY OF THE INVENTION  
         [0006]    Therefore, in view of the problems associated with the above torque transfer assemblies, it is an object of the present invention to provide a reinforced torque transfer assembly that 1) can withstand relatively high shear stresses, 2) can be used with existing torque transfer assemblies with only minimal modification, and 3) does not significantly increase the cost of the torque transfer assembly.  
           [0007]    These and other objectives are met by the reinforced torque transfer assembly of the present invention. For the purpose of demonstration, the torque transfer assembly is shown in use in a sprocket assembly in particular a sprocket assembly used to transmit torque to an auger system used in an agricultural application. This example is not intended to limit the scope of the invention.  
           [0008]    In one aspect of the present invention, a torque transfer assembly is composed of at least one disk member and a shaft. The disk member is attached to the shaft with at least one fastener that is reinforced with a tube key. The disk member may be a sprocket or the like wherein the sprocket is mounted onto the shaft with the reinforced fastener so that the tube key is positioned on a portion of the fastener that experiences shear stress. In another aspect of the present invention, a method of driving an auger with the reinforced torque transfer assembly is claimed. In the method, a torque transfer assembly is presented. The torque transfer assembly is composed of at least a first disk member and a second disk member attached to a shaft with reinforced fasteners. The auger is attached to the torque transfer assembly. Finally, the first disk member is rotated in order to drive the auger.  
           [0009]    In another aspect of the present invention, a mixing tank, i.e. for mixing hay and the like, composed one or more augers each connected to a torque transfer assembly. The torque transfer assembly is composed of a at least one disk mounted onto a shaft with tube-key reinforced fasteners.  
           [0010]    The present invention will be better understood from the following detailed description of the invention, read in connection with the drawings as hereinafter described. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a front end view of a prior-art bolted torque transfer assembly;  
         [0012]    [0012]FIG. 2 is a cross-sectional view of the bolted torque transfer assembly of FIG. 1 taken along lines  2 - 2 , showing the engagement of bolts through stacked sprockets and into a stub shaft;  
         [0013]    [0013]FIG. 3 is a front end view of an embodiment of a reinforced torque transfer assembly according to the invention, showing stacked sprockets mounted on the stub shaft;  
         [0014]    [0014]FIG. 4 is a cross-sectional view of the reinforced torque transfer assembly of FIG. 3 taken along lines  44 , showing the engagement of a tube key and bolts through the stacked sprockets and into the stub shaft;  
         [0015]    [0015]FIG. 5 is a cross-sectional view of another embodiment of a reinforced torque transfer assembly, showing stacked sprockets;  
         [0016]    [0016]FIG. 6 is a cross-sectional view of another embodiment of a reinforced torque transfer assembly, showing a single sprocket mounted on the stub shaft;  
         [0017]    [0017]FIG. 7 is a perspective view of the reinforced torque transfer assemblies of FIGS.  3 - 6 , mounted in an auger-type feed mixer; and  
         [0018]    [0018]FIG. 8 is a perspective view of the assembly of FIG. 1 attached to an auger drive shaft.  
         [0019]    [0019]FIG. 9. is a perspective view of a prior-art mixer assembly. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    The invention provides an apparatus and method of power transfer that increases the torsional load carrying capacity of a torque transfer assembly, wherein the assembly is composed of disk members held together with fasteners such as threaded bolts.  
         [0021]    [0021]FIGS. 1 and 2 illustrate a sample prior-art torque transfer assembly  10 . As shown by example of a sprocket assembly, assembly  10  includes a shaft such as stub shaft  12 , a large diameter sprocket  14 , a sprocket spacer  16 , and a small diameter sprocket  18 . The sprockets  14 ,  18  are stacked together with spacer  16  therebetween, and mounted onto stub shaft  12  with threaded bolts  20 . Specifically, threaded bolts  20  extend into a bore  21  through sprockets  14 ,  18  and spacer  16 , and a bore  22  in stub shaft  12 . Bores  21 ,  22  are substantially parallel to the rotational axis of the shaft such as stub shaft  12 . The function of bolts  20  is to keep sprocket spacer  16  and the rest of the sprocket assembly connected to stub shaft  12 . However, in the prior art assembly  10 , the bolt threads cause stress concentrations on the bolt shaft. Therefore, the threaded portion  24  on bolts  20  is the weakest part of the bolt. Problematically, this part of bolt  20  supports the highest amount of shear stress with the assembly being linked to and supported at joint  25  between sprocket  14  and stub shaft  12  by threaded part  24  of bolts  20 . Consequently, bolts  20  linking sprockets  14 ,  18  to stub shaft  12  can fail due to shear stress. This can also be true for non-threaded fasteners.  
         [0022]    [0022]FIGS. 3 and 4 depict an embodiment of a reinforced torque transfer assembly  30   a , according to the invention. The assembly  30   a  includes a shaft such as a stub shaft  32 , a large diameter sprocket  34 , a sprocket spacer  36 , and a small diameter sprocket  38 . The sprockets  34 ,  38  are stacked with spacer  36  therebetween, and large sprocket  38  mounted on stub shaft  32 .  
         [0023]    Advantageously, assembly  30   a  provides a plurality of thick walled dowels or tube keys  40  that mate into a bore  42  in stub shaft  32 . Preferably, the tube key thickness about 7 millimeters (mm). Further, the tube keys  40  are preferably made from carbon steel tubing. Bolts  44  are then mounted through sprockets  34 ,  38  and into tube keys  40  in stub shaft  32 . Therefore, the joint  45  between sprocket  34  and the stub shaft  32  is strengthened by the tube keys  40 . The new assembly  30   a  transfers load to the combined tube key  40  and bolt  44  assembly.  
         [0024]    [0024]FIG. 5 depicts another embodiment of a reinforced torque transfer assembly according to the invention, designated as  30   b  . The drive assembly  30   b  includes a stub shaft  32 , a large diameter sprocket  34  and a small diameter sprocket  38 , with a spacer  36  therebetween. The tube key is designated as  40 . The drive assembly  30   b  is similar to the stacked assembly  30   a  except that the position of the sprockets are reversed, with small sprocket  38  being mounted on the stub shaft  32 .  
         [0025]    [0025]FIG. 6 depicts another embodiment of a reinforced torque transfer assembly, designated as  30   c . The drive assembly  30   c  is composed of a single sprocket  46  mounted on a stub shaft  32 . The tube key is designated as  40 .  
         [0026]    [0026]FIG. 7 illustrates the arrangement of the various reinforced torque transfer assemblies in a feed mixer composed of stacked augers within a mixing tank. The reinforced torque transfer system can also be advantageously used in a feed mixer such as those disclosed in U.S. Pat. Nos. 4,597,672, 4,506,990 and 4,741,625 (Neier), incorporated herein by reference, and other torque-driven mechanisms.  
         [0027]    As shown, feed mixer  50  is composed of stacked augers including two top augers  54 ,  56  positioned above two bottom augers (not shown). Each of the augers include central shafts that are rotatably supported and extend through the rearward end wall  57  of the mixer. The two bottom augers rotate clockwise to move hay or other feed material to the front  52  of mixer  50  where the material moves upward to the two top augers  54 ,  56 . Top augers  54 ,  56  rotate to the inside in the direction of arrow  58 , to move material to the back end  60  of mixer  50  where the material cascades to the two bottom augers, whereupon the mixing and blending process is repeated. Upon engagement of the drive linkage, which includes reinforced torque transfer assemblies  30   a - d , the upper and lower augers are rotated to cause movement of feed in a circulating path.  
         [0028]    The reinforced torque transfer assemblies  30   a - d  are shown mounted in the rear end  60  of an auger-type mixer  50 . At the front end  52  of mixer  50 , a power take-off shaft  51  (as shown in a similar prior art mixer in FIG. 9) connects to a tractor. A line shaft  53  extends underneath mixer  50  from front end  52  to rear end  60 , and is connected to a drive mechanism. On the lower right side of mixer  50 , assembly  30   a  (depicted in FIGS. 34) is connected to a bottom auger  61  (FIG. 8), and preferably includes a large diameter sprocket  34  positioned behind a small diameter sprocket  3   8  with spacer  36  therebetween.  
         [0029]    On the lower left side of the mixer, assembly  30   b  (depicted in FIG. 5) is connected to the left hand bottom auger, and preferably includes a large diameter sprocket  34  positioned in front of the small diameter sprocket  38  (shown in phantom), with spacer  36  therebetween.  
         [0030]    On the upper right side of the mixer, a torque transfer assembly  30   d  is connected to the top auger  56 . Assembly  30   d  is similar to that shown in FIG. 5, except that it is preferably composed of a single medium-sized sprocket (rather than the large-sized sprocket of assembly  30   b ), and sprocket  38  is replaced by a dummy plate.  
         [0031]    On the upper left side of the mixer, drive mechanism  30   c , connected to the top auger  54 , is a stacked arrangement as shown in FIG. 6. Sprocket  46  is connected by chain  78  to a preferably small sprocket  38  (shown in phantom) positioned below on the lower left side of the mixer The combined assembly preferably employs two stages of reduction to power the bottom auger drives, and three stages of reduction to power the top auger drives, by means of the change in size of the sprocket and chain connection between sprockets. Different stages of power reduction may be achieved by replacing the torque transfer assembly sprockets with sprockets of different sizes.  
         [0032]    Line shaft  51  extends underneath the mixer and powers a small drive sprocket (not shown) located in the center lower portion of the rear of the mixer. The small drive sprocket is connected by a chain to a large diameter sprocket  66  in the upper middle section. Referring again to FIG. 7, a center jack-shaft is mounted on the large upper sprocket  66 , and supports a small diameter drive sprocket (located behind sprocket  66 ). The small drive sprocket is connected by a chain  72  to the large diameter sprocket  34  mounted on the left-bottom auger positioned beneath the top auger  54 . Small drive sprocket is also connected by a chain  74  to the large diameter sprocket  34  mounted on the right-bottom auger positioned beneath right-top auger  56 . On the right-bottom side, small diameter drive sprocket  38  is stacked in front of the large sprocket  34 , and is connected by a chain  76  to sprocket  34  mounted on top-right auger  56 . On the left-bottom side, small diameter drive sprocket  38  (shown in phantom) is stacked behind the large sprocket  34 , and is connected by a chain  78  to sprocket  46  mounted on top auger  54 .  
         [0033]    The drive or the torque transfer assemblies  30   a - d  are bolted to the lower and upper auger drive shafts and auger tube assemblies, preferably with multiple, evenly spaced bolts. Such an attachment is shown in FIG. 8, with regard to assembly  30   a  attached to the bottom auger  61 . Upon engagement of the drive linkage, the upper and lower augers arc rotated to cause movement of feed in a circulating path. In particular, the bottom sprockets  34  on either side of the mixer drive the bottom augers, and torque is transferred to sprockets  38  in the stack, which, in turn, drive the upper sprockets  46  and  34 , that respectively drive the top augers  56 ,  54 .  
         [0034]    The reinforced drive of the present invention improves reliability in tough hay processing and mixing situations. Tube keys  40 , which are “doweled” through the sprocket and into the stub shaft  32 , significantly increase the shear stress capacity, increasing the shear strength by about three times compared to previously known designs. The use of the tube keys  40  also eliminates placing the greatest shear stress on the weakest part of the bolt, i.e., the threaded section. Thus, as the chain pulls on and rotates the sprocket, the bolts resist tension and maintain the sprockets mounted on the stub shaft.  
         [0035]    The invention has been described by references to detailed examples and methodologies. These examples are not meant to limit the scope of the invention. Variations within the concepts of the invention are apparent to those skilled in the art.