Abstract:
A swivel nut comprising a body ( 10 ) having a threaded bore ( 130 ), the body comprising a ridge ( 11 ) which circumferentially extends about an outer surface, the body further comprising a first surface ( 12 ) which extends normal to a body bore centerline (CL), a tapered member ( 20 ) having a tapered surface ( 22 ) and a bore ( 23 ), the tapered member further comprising a second surface ( 23 ) which extends normal to the body bore centerline and which second surface cooperatively engages the first surface, the tapered member comprising a groove ( 21 ) which extends about an inner surface, and the groove cooperating with the ridge to connect the body and the tapered member while allowing the tapered member rotational movement with respect to the body.

Description:
FIELD OF THE INVENTION 
     The invention relates to a swivel nut, and more particularly, to a swivel nut having a ridge and groove snap-on torque cone. 
     BACKGROUND OF THE INVENTION 
     A common problem encountered by freight haul tractor trailers, as well as smaller trailers used for non-commercial purposes such as recreational trailers, is the loosening of the lug nuts on the wheels of the trailer. 
     A common problem results from methods used to secure nuts to lug bolts on new truck and trailer wheels. Unless properly addressed “seating-in” during initial use can result in a reduction of the clamp force, and thereby the torque, which holds the wheel to the axle hub. This can over time create a gap between the nut and the wheel which enables the initially tight nuts to loosen up. 
     Further, the stacking of components on a vehicle wheel hub creates a cumulative thickness of the stacked parts. The initial torque can force the material of the stacked components to yield, thereby allowing the nuts to loosen by “bleeding off” the initial torque and preload, again, causing the nut to loosen. 
     Loss of torque can also occur as a result of long storage periods where the wheel assembly is subjected to repeated cycles of heating and cooling. 
     Once the nuts have loosened, the wheel is able to rock and wobble back and forth on the lug bolts. After a period of time, the lug hole diameter in the wheel can be significantly enlarged, damaging the wheel as well as severely degrading the stability of the trailer, rending it uncontrollable. Also, relative movement of the wheel can result in fatigue failure of the lug bolts, causing catastrophic separation of the wheel from the axle hub. For example, in an emergency or panic stop, once loosened under hard application of the brakes the wheel can shear off the lug bolts, thus rendering the trailer or vehicle uncontrollable. Once detached the wheel can become a dangerous projectile as well, capable of seriously injuring others. 
     This situation can be further aggravated by the accumulation of debris on the various engaged, load bearing surfaces of the lug nut system. 
     Representative of the art is U.S. Pat. No. 6,592,314 which discloses a wheel nut and washer assembly for securing a wheel to a motor vehicle axle. The wheel nut includes a body having a longitudinal axis, the nut body also having an axial threaded aperture and a pair of ends, one end being in the form of a smooth steel external surface. The wheel nut also includes a steel washer having an end terminating in a smooth annular surface in surface-to-surface engagement with the body end thereby maintaining axially alignment of the body and washer enabling relative movement of said body and washer about said axis. A decorative cap on the assembly is configured so that it holds the washer on the nut, a gap between the cap and washer to enable the washer to freely rotate and move laterally relative to the nut. 
     What is needed is a swivel nut having a ridge and groove snap-on torque cone. The present invention meets this need. 
     SUMMARY OF THE INVENTION 
     The primary aspect of the invention is to provide a swivel nut having a ridge and groove snap-on torque cone. 
     Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
     The invention comprises a swivel nut comprising a body having a threaded bore, the body comprising a ridge which circumferentially extends about an outer surface, the body further comprising a first surface which extends normal to a body bore centerline, a tapered member having a tapered surface and a bore, the tapered member further comprising a second surface which extends normal to the body bore centerline and which second surface cooperatively engages the first surface, the tapered member comprising a groove which extends about an inner surface, and the groove cooperating with the ridge to connect the body and the tapered member while allowing the tapered member rotational movement with respect to the body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention. 
         FIG. 1  is a cross-sectional view of the swivel nut. 
         FIG. 2  is a perspective view of the swivel nut. 
         FIG. 3  is an end view of the swivel nut. 
         FIG. 4A  is a side plan view of the swivel nut. 
         FIG. 4B  is a side plan view of an alternate embodiment. 
         FIG. 5  is an end view of the swivel nut. 
         FIG. 6  is a cross-sectional view of the swivel nut installed on a wheel hub. 
         FIG. 7  is a cross sectional view of an alternate embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a cross-sectional view of the swivel nut. Swivel nut  100  comprises nut  10  and torque cone  20 . Nut  10  comprises hexagonal flanges for engaging a known tool such as a wrench, ratchet or wheel socket. 
     Torque cone  20  and nut  10  are engaged by a ridge  11  on the nut  10  and a groove  21  which in combination comprises the torque cone snap-on feature. Groove  21  is disposed on an inner surface circumference of skirt  24 . The diameter of groove  21  is selected according to the thickness of the skirt  24 . Skirt  24  has an inner diameter (D 1 ). 
     Ridge  11  is disposed on an outer surface circumference of nut  10  and has a diameter (D 2 ). Ridge  11  diameter (D 2 ) is of a sufficient magnitude to fully engage groove  21 , thereby preventing torque cone  20  from separating from nut  10  once joined. However, at the same time the engagement between ridge  11  and groove  21  has clearance sufficient to allow some movement and free rotation of torque cone  20  about nut  10 . Hence diameter (D 2 ) is slightly greater than diameter (D 1 ) in order to achieve an interference fit only during installation which requires skirt  24  to be slightly expanded when nut (body)  10  and the torque cone  20  (tapered member) are connected or “snapped” together. The ridge and groove do not otherwise contribute to torque transmission. 
     Torque cone surface  23  engages nut surface  12 . Surfaces  23 ,  12  extend substantially normal to a bore centerline CL of the nut  10 . Gap  30  between cone  20  and nut  10  assures clearance so that the clamping force is only exerted through surfaces  23 ,  12 . Surfaces  23 ,  12  are only subjected to clamping forces having a vector that is substantially parallel to a nut centerline CL. Surfaces  23 ,  12  have a reduced coefficient of friction to enhance slipping between them. The materials may comprise steel, ceramic material, or a hardened coating. 
     An internal bore  13  of nut  10  is threaded to engage a threaded stud  400  (see  FIG. 6 ). Stud  400  is a component of a vehicle wheel hub, such as on a trailer axle. However, it should be noted that the inventive swivel nut may be used in any threaded application. 
     Surface  22  of torque cone  20  comprises a cone angle α thereby giving a taper to properly engage a wheel flange hole  201 , see  FIG. 6 . Cone angle α may be in the range of approximately 60° to approximately 90°, see  FIG. 4 . The preferred cone angle is approximately 60°. Wheel flange hole  201  has a nut seat angle β which cooperates with surface  22  (see  FIG. 6 ). Swivel surface  22  self aligns with a wheel flange hole  201  during use. 
     Bore  230  concentrically engages stud  400 . Bore  230  has a slightly larger diameter than nut bore  13  since bore  230  is not threaded and does not contact the stud as a feature of operation. 
     A preload (L) is the desired design preload in the stud. The desired stud preload (L) is achieved by application of the installation torque on the nut  10 . Selection of the proper stud preload assures proper service for the swivel nut  10  and ultimate retention of the wheel on a hub. 
     Use of the torque cone  20  compensates for the effects of nut  10  being loosened during operation. The torque cone maintains the proper preload on the stud or bolt if the components yield or are otherwise misaligned through use. This is primarily due to the flat surfaces  23 ,  12  and the substantially normal position of the surfaces with respect to the nut centerline. This arrangement provides that the force generated by the nut torque acts normally to the torque cone surface  23  thereby assuring optimum claiming force. During installation the torque cone  20  does not rotate in wheel hole  201 . Only nut  10  rotates with respect to torque cone  20  as nut  10  is torqued on stud  400 . Surface  23  slides upon surface  12  during installation as nut  10  is turned. 
     The following table is offered to illustrate a range of approximate torque values that are based upon the diameter of the stud  400 . These figures are only offered by way of example and are not intended to limit the range of applications for the inventive swivel nut. 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Stud Diameter 
                 Torque Range 
               
               
                   
                   
               
             
             
               
                   
                 ½″ 
                  ~60 to 120 ft/lbs 
               
               
                   
                  9/16″ 
                  ~90 to 170 ft/lbs 
               
               
                   
                 ⅝″ 
                 ~190 to 325 ft/lbs 
               
               
                   
                   
               
             
          
         
       
     
     In an example system, a set of swivel nuts are each torqued down on a ½″ stud ( 400 ) to mount a wheel ( 200 ) on a trailer hub ( 300 ). The number of studs/swivel nuts utilized per wheel can include any appropriate number including but not limited to 4, 5, 6, or 8. The torque in this example situation is approximately 120 ft/lbs and the clamp force between each swivel nut and the hub in this example is approximately 15,000 pounds. The proper clamp force prevents the wheel from moving on the hub during operation. If the clamp force is too low the wheel will move causing a periodic bending moment to be imposed on the studs. The periodic bending moment will ultimately cause the studs to fail. 
     The desirable characteristic of the swivel nut has the effect of enhancing and maintaining the proper clamping force between the swivel nut and the wheel. The clamping force assures that the load on each stud  400  is a tensile load acting axially instead of a periodic bending moment which can cause premature failure of the stud. 
     During installation only nut  10  is rotated about stud  400 . Torque cone  20  does not rotate with respect to stud  400  or wheel  200 , see  FIG. 6 . Surfaces  23  and  12  slide upon each other as nut  10  is torqued down. Since the forces acting on surfaces  12 ,  23  are substantially normal to surfaces  12 ,  23 , the frictional force generated is substantially less than in the case of a prior art nut wherein a tapered surface engaged with a wheel is moved by rotation. In turn, a greater percentage of the torque applied to the inventive swivel nut during installation goes into preloading stud  400  instead of being used to overcome friction between a nut tapered surface and the wheel or between the nut threads and the stud threads. This in turn results in a significantly greater clamp force being applied to the wheel since the stud preload is greater for a relatively lesser torque. 
       FIG. 2  is a perspective view of the swivel nut. Torque cone  20  is coaxially engaged with nut  10 . Surface  13  is threaded to engage a stud (not shown). Only nut surface  13  threadably engages stud  400 . Surface  25  is not threaded and has a diameter that exceeds the diameter of surface  13 . 
       FIG. 3  is an end view of the swivel nut. Bore  130  extends through nut  10 . 
       FIG. 4A  is a side plan view of the swivel nut. Gap  30  is disposed between torque cone  20  and nut  10  to assure that the clamping force is only transmitted through the engagement of surfaces  23 ,  12 . 
       FIG. 4B  is a side plan view of an alternate embodiment. In this alternate embodiment surface  22   a  is arcuate to form a convex surface that engages a cooperating surface in a wheel hole. 
       FIG. 5  is an end view of the swivel nut. Bore  230  extends through torque cone  20 . Bore  230  is coaxially aligned with bore  130 . 
       FIG. 6  is a cross-sectional view of the swivel nut installed on a wheel hub. Swivel nut  10  is threaded onto threaded stud  400 . Stud  400  is typically press fit into a hub  300 . Hub  300  is typically attached to a vehicle or trailer axle (not shown). Wheel  200  is fastened to hub  300  by one or more swivel nuts  10 . Wheel  200  comprises a wheel hole  201  which receives the swivel nut  10 . Stud  400  projects through wheel hole  201 . 
       FIG. 7  is a cross sectional view of an alternate embodiment. Belleville spring washer  60  is disposed between the nut  10  and the torque cone  20 . More particularly, Belleville spring washer  60  is disposed and compressed between surface  12  and surface  23 . 
     Belleville springs demonstrate known and predictable characteristics in compression. Proper selection allows a predetermined load, or in this case a stud preload, to be substantially constant over a significant spring deflection range. This means the nut  10  can unscrew a substantial amount during which washer  60  will deflect while maintaining a constant minimum preload on the stud  400 , see  FIG. 6 . Further, a constant preload can be maintained for a greater deflection by stacking washers in series. 
     In an alternate embodiment Belleville spring washer  60  can be replaced with a flat washer. The surface coefficient of friction of a flat washer may be selected in order to minimize sliding friction between the washer and surfaces  23  and  12 , thereby optimizing the stud preload for a given installation torque. 
     Preload L is the desired preload in the stud  400 . The desired stud preload L is achieved by the installation torque on the nut  10 . Selection of the proper stud preload is discussed above and assures proper service for the swivel nut  10  and retention of the wheel on a hub. 
     Use of the washer  60  compensates for the effects of nut  10  being loosened during operation. Washer  60  maintains the proper preload on the stud or bolt even if the nut is partially unscrewed from the stud or bolt, or if the components yield or are otherwise misaligned through use. For example, unintended partial rotation of nut  10  may occur during operation if a flat of the nut is struck by a piece of debris. Repeated strikes might otherwise loosen the nut, but the washer  60  enhances the ability of the nut to maintain proper preload on the stud or bolt, thereby assuring sufficient clamping force. Mechanical fatigue or yielding by the components may also cause torque to bleed off as well, but the ability of the nut to resist such torque bleed is substantially enhanced by use of the washer  60 . 
     Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.