Abstract:
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 non-cylindrically-symmetrical stud attached to the axle that is concentric with the axis of rotation of the wheel and axle, attaching the wheel to the axle.

Description:
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 torque and power efficiently from the axle to the wheel.  
           [0003]    A common method employs a plurality of lug studs circumferentially spaced around the rotational axis of the axle. The lug studs are supported by a flange attached to the axle. The wheel is mounted on these lug studs through holes in the wheel that allow the studs to pass through the wheel. Lug nuts are screwed onto the lug studs, forcing the wheel against the flange as the lug nuts are tightened. The lug nuts retain the wheel on the axle and the torque and power of the axle are transferred to the wheel via the lug studs. The plurality of lug studs 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 stud 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 studs. 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 torque and power transfer from the rotating axle to the wheel; (b) provide quick and easy attachment and detachment of the wheel from the axle; (c) provide redundancy for power transfer and (d) 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 a preferred embodiment of the invention, a system is provided that has: (a) an axle having an indentation at a wheel-coupling end for a wheel hub; (b) a non-cylindrically-symmetrical lug stud, concentric with the axle, extending from the wheel-coupling end of the axle; (c) a wheel having a non-cylindrically-symmetrical clearance hole to admit the lug stud, the clearance hole at the center of the wheel; (d) a wheel hub, that is inserted into an indentation in the end of the axle; and (e) a fastener for attaching the wheel to the lug stud.  
           [0006]    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 rotational 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 on the rotational axis of the wheel with a lug stud not possessing cylindrical-symmetry about the rotational axis of the axle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 shows a personal transporter.  
         [0008]    [0008]FIG. 2 shows a sectional side view of an embodiment of the present invention.  
         [0009]    [0009]FIG. 3 shows an exploded view of the wheel assembly of an embodiment of the present invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0010]    The subject matter of this application is particularly suited for application to a personal transporter such as that described in U.S. Pat. No. 5,971,091, issued Oct. 26, 1999, which may require periodic wheel maintenance, which patent is incorporated herein by reference in its entirety. Such a personal transporter employing an embodiment of the present invention is shown in FIG. 1 and designated generally by numeral  10 . The transporter includes a plurality of wheels  15 , a motor  20 , a controller  25 , and an axle  30 . While unstable when not powered, transporter  10  maintains balance during normal operation by sensing parameters such as θ and {dot over (θ)}, and applying torque according to a control law, as described in detail in the &#39;091 patent. Similarly, the subject matter of this application is suited for the human transporter described in U.S. Pat. No. 5,701,965, issued Dec. 30, 1997, also incorporated herein by reference.  
         [0011]    Precise registration of the wheel and axle are particularly critical to a balancing vehicle, such as personal transporter  10  because the wheel must respond in an instantaneous and predictable manner to controller commands. Thus, use of multiple attachment points between axle and wheel would appear to be required. Preferred embodiments of the present invention achieve precise registration with a single attachment point.  
         [0012]    [0012]FIG. 1 shows a sectional side view of one embodiment of the present invention which advantageously couples a wheel to an axle. An axle  100  has a rotational axis  120 . The wheel-coupling end of the axle has a tapered indentation  125  centered on the rotational axis  120 . A lug stud  130 , extends from the tapered indentation  125  and has an axis that is parallel to and coincident with the rotational axis  120 . The lug stud is non-cylindrically-symmetrical about the rotational axis and may be, for example without limitation, hexagonally shaped when viewed in cross-section perpendicular to the rotational axis. The lug stud is removable from the axle, but is locked in place while the axle is operational by means of a press-fit technique or any one of a number of means known in the art for securing lug studs to axles.  
         [0013]    A wheel  140  includes a hub  145  that is centered on the wheel&#39;s rotational axis  160  and extends along the wheel&#39;s rotational axis  160 . 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  160  of the wheel. The hub  145  has a tapered end  150  that is shaped and sized to fit into the tapered indentation  125  such that when the hub  145  is seated in the tapered indentation  125 , the rotational axis of the axle  100  and the rotational axis of the wheel are coincident. The wheel  140  includes a clearance hole  155 , the hole having an axis that is parallel to and coincident with the rotational axis  160  of the wheel. The clearance hole is sized and shaped to allow insertion of the lug stud  130 .  
         [0014]    A fastener  170 , such as a lug nut, attaches to the lug stud  130 , securing the wheel  140  to the axle  100 . As the fastener  170  is tightened, the wheel hub  140  is forced against the axle indentation  125 , producing a force component normal to the tapered surface of the hub  150 . The normal force generates a frictional force on the tapered surface of the hub and the tapered surface of the indentation of the axle thereby efficiently transferring torque and power from the rotating axle to the wheel. If the fastener  170  loosens and the tapered surfaces begin to lose contact, the non-cylindrically-symmetrical lug stud  130  mated to the similarly shaped clearance hole  155  places the lug stud in torsion and, thereby, creates a torque on the wheel that continues to drive the wheel. By providing a non-cylindrically-symmetrical lug stud mated to a similarly shaped clearance hole in the wheel, the present invention provides a redundant drive mechanism for the wheel, while using only a single lug stud and fastener. FIG. 2 shows an exploded view of the wheel assembly and the lug stud of an embodiment of the present invention.  
         [0015]    Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention. These and other obvious modifications are intended to be covered by the appended claims.