FIELD OF THE INVENTION  
         [0001]    The present application is directed to an apparatus and method for attaching a wheel to an axle.  
         BACKGROUND OF THE INVENTION  
         [0002]    Many methods of attaching a wheel to an axle are known in the art. A wheel attachment must both secure the wheel to the axle and transfer angular momentum efficiently from the axle to the wheel.  
           [0003]    A common method employs a plurality of lug bolts circumferentially spaced around the longitudinal axis of the axle. The lug bolts are supported by a flange attached to the axle. The wheel is mounted on these lug bolts through holes in the wheel that allow the bolts to pass through the wheel. Lug nuts are screwed onto the lug bolts, forcing the wheel against the flange as the lug nuts are tightened. The lug nuts retain the wheel on the axle and the angular momentum of the axle is transferred to the wheel via the lug bolts. The plurality of lug bolts provides redundancy to the system since a loose lug nut will not cause the wheel to separate from the axle nor will it cause the wheel to slip relative to the rotation of the axle. The disadvantage of using more than one lug bolt to secure the wheel to the axle is the added time required to attach or detach the wheel since more than one lug nut must be screwed or unscrewed from the lug bolts. A second disadvantage is the additional cost associated with manufacturing the flange portion of the axle.  
           [0004]    An improved approach for securing a wheel to an axle should: (a) maintain efficient angular momentum transfer from the rotating axle to the wheel; (b) provide quick and easy attachment and detachment of the wheel from the axle; and (c) improve manufacturability by simplifying the design of the wheel and axle mating surfaces. Embodiments of the present invention address each of these needs.  
         SUMMARY OF THE INVENTION  
         [0005]    In accordance with preferred embodiments of the present invention, a system is provided for securing a wheel to an axle. The system has (a) an axle with a wheel-coupling end, having an indentation for insertion of a wheel hub; (b) a threaded bolt hole parallel to the longitudinal axis of the axle and offset from the longitudinal axis; (c) a wheel having a clearance hole parallel to and offset from the rotational axis of the wheel and a hub that is inserted into the indentation in the wheel-coupling end of the axle; and (d) a bolt having a threaded end for insertion through the clearance hole, for securing the wheel to the axle.  
           [0006]    In accordance with a further embodiment of the invention, a system is provided that has: (a) an axle having an indentation at a distal end for a wheel hub; (b) a lug stud, nonconcentric with the axle, extending from the distal end of the axle; (c) a wheel having a clearance hole to admit the lug stud, the clearance hole offset from the center of the wheel; (d) a wheel hub, that is inserted into an indentation in the end of the axle; and (e) a lug nut for attaching the wheel to the lug stud  
           [0007]    In accordance with a further embodiment of the invention, there is provided a method for securing a wheel to an axle. The method has the steps of: aligning the rotational axis of the wheel with the longitudinal axis of the axle; inserting the wheel hub into an indentation in an end of the axle; and fastening the wheel to the axle at a single point offset from the rotational axis of the wheel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 shows a sectional side view of one embodiment of the present invention.  
         [0009]    [0009]FIG. 2 shows a sectional side view of another embodiment of the present invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0010]    [0010]FIG. 1 shows a sectional side view of one embodiment of the present invention which advantageously couples a wheel to an axle. An axle  120  has a longitudinal axis  100 . The wheel-coupling end of the axle has a tapered indentation  125  centered on the axle&#39;s longitudinal axis  100 . Wheel  140  includes a hub  142  that is centered on the wheel&#39;s rotational axis, extending along the wheel&#39;s rotational axis. The term “wheel” as used in this description and in any appended claims will be understood to include any element that turns about an axis of rotation, transforming angular momentum to linear momentum by rolling along a surface. As used in this description and in any appended claims, the term “hub” will be understood to encompass any arbitrarily-shaped protrusion from the wheel that is concentric with the rotational axis of the wheel.  
         [0011]    The hub  142  has a tapered end  144  that is shaped and sized to fit into the tapered indentation  125  such that when the hub  142  is seated in the tapered indentation  125 , the longitudinal axis of the axle  100  and the rotational axis of the wheel are coincident. The hub  142  includes a clearance hole  146 , the hole having an axis that is parallel to, but not coincident with, the rotational axis  100  of the wheel. The clearance hole may have a counter-bore  148  and is sized to allow the insertion of a fastener, such as a bolt  160  with a bolt shaft  162 , into the clearance hole  146 . The bolt  160  is screwed into the threaded bolt hole  122  in the axle  120 , securing the wheel  140  to the axle  120 .  
         [0012]    As the bolt  160  is tightened, the wheel  140  is forced against the axle, producing a force component normal to the tapered surface of the hub  142 . The normal force generates a frictional force on the tapered surface of the hub and the tapered surface of the indentation of the rotating axle thereby efficiently transferring the angular momentum of the rotating axle to the wheel. If the bolt loosens and the tapered surfaces begin to slip, the offset of the bolt from the longitudinal axis of the axle places the lug bolt in shear and therefore creates a torque on the wheel that continues to drive the wheel. By offsetting the clearance hole, and, therefore, the bolt, from the rotational axis of the wheel, the present invention provides a redundant drive mechanism for the wheel, while using only a single bolt. ? ? ?  
         [0013]    [0013]FIG. 2 shows a sectional side view of another embodiment of the present invention. An axle  220  has a longitudinal axis of rotation  200 . The distal end of the axle has a tapered indentation  225  that is centered on the longitudinal axis of the axle  200 . A fastener, such as a lug stud  228 , extends from the bottom  227  of the tapered indentation  225  and has an axis that is parallel to but not coincident with the longitudinal axis of the axle  200 . A wheel  240  includes a hub  242  that is centered on the wheel&#39;s rotational axis and extends along the wheel&#39;s rotational axis. The hub  242  has a tapered end  244  that is shaped and sized to fit into the tapered indentation  225  such that when the hub  242  is seated in the tapered indentation  225 , the longitudinal axis of the axle  200  and the rotational axis of the wheel are coincident. The hub  242  includes a clearance hole  246  positioned and sized to allow the lug stud  228  to pass through the hub  242 . A lug nut  260 , secures the wheel  240  to the axle  220 .
An apparatus and method for attaching a wheel to an axle. The apparatus comprises a wheel with a hub for insertion into an indentation in the end of the axle and a single bolt that is offset from the axis of rotation of the wheel and axle and that attaches the wheel to the axle.