Abstract:
A self-tightening, self-centering fastener device having a pair of washers having cam surfaces that generate a wedging force. One of the washers has a raised, annular crown for seating in an annular seat in the workpiece.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a self-tightening threaded fastener with multiple locking washers. In particular, it relates to a threaded nut having self-tightening means and a self-centering structure. 
     A variety of self-tightening fastening devices have been disclosed in the prior art. Such fastener devices accommodate a workpiece exposed to vibration. Some prior art devices may be found in U.S. Pat. No. 3,263,727 which issued to Arthur B. Herpolsheimer on Aug. 2, 1966; and U.S. Pat. No 3,417,802 which issued to Carl O. Oldenkott on Dec. 24, 1968. A commercially-available form of such device has long been marketed as a Disc-Lock, vibration proof, self-tightening, locking device. 
     Such devices usually have one or more washer-shaped pieces having inclined cams on one side and a series of ridges on the other. The washers are mounted so that the cam surfaces will mate. In a typical situation, the washers are mounted on a stud between a nut and the workpiece. 
     Vibration or shock will cause the stud or bolt to elongate. The nut tends to rotate loose. A self-tightening locking device prevents this since the cam rise angle is greater than the lead angle of the thread on the bolt. As the nut rotates relative to the washer, the preload is actually increased, further locking the nut. 
     When the bolt contracts, the inclined planes of the cam causes the nut to rotate back to its original position. The result is a fastening system that is vibration proof. 
     One shortcoming of a commercially available, self-tightening fastener is that it cannot be substituted for certain types of wheel nuts of the type having a raised partially spherical crown. The partially spherical crown is seated in a conical or spherical recess. 
     A form of a self-centering fastener assembly is disclosed in U.S. Pat. No. 4,362,449 which issued Dec. 7, 1982 to Emil J. Hlinsky. 
     SUMMARY OF THE INVENTION 
     The broad purpose of the present invention is to provide an improved self-centering, self-tightening fastener device that can be employed on a workpiece requiring a self-centering nut. In the preferred embodiment of the invention, one of the non-flexing locking washers, in contact with the workpiece, has a continuous annular shoulder or crown. The annular shoulder has a somewhat conical configuration adapted to seat into the conical or spherical seat of the workpiece so that when the nut is tightened, it forms a self-centering fastener assembly. 
     Still further objects and advantages of the invention will become readily apparent to those skilled in the art to which the invention pertains upon reference to the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the preferred assembly on a stud extending from a workpiece. 
     FIG. 2 is a view as seen along lines 2--2 of FIG. 1. 
     FIG. 3 is an enlarged, fragmentary view of the preferred fastener assembly. 
     FIG. 4 is a top view of the two washers. 
     FIG. 5 is an exploded, cross-sectional view of a fastener and multiple locking washer assembly according to this invention. 
     FIG. 6 is a view of a clip in the assembly in FIG. 1. 
     FIG. 7 shows a bottom view of the upper washer. 
     FIG. 8 is a top view of the bottom washer. 
     FIG. 9 is a bottom view of the nut. 
     FIG. 10 is a bottom view of the lower washer. 
     FIG. 11 shows the geometrical relations of the cam surfaces in the assembly of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The drawing shows components to form a self-centering, self-tightening fastener assembly including a nut 11 having a thread 12 with a rise angle &#34;A&#34;. One axially directed face of the nut has a wedge-action cam surface 13, FIG. 9, comprising a plurality of cam elements 14, each of which has a sloping surface 15 and an abutment surface 16. Referring to FIG. 11, the slope of each surface 15 has a steeper rise angle &#34;B&#34; than the rise angle &#34;A&#34; of thread 12 and in the same direction of rotation, while the slope of each surface 16 slopes steeply in the opposite direction to the beginning of the next cam element 14. 
     Nut 11 has a typical hexagonal configuration with six driving surfaces 18 that are parallel to the central axis 19 of the nut. Accordingly, surface 13 has six cam elements 14 angularly spaced by an angle of 60°, with each of the abutment surfaces 16 extending generally radially out to a respective one of the corners defined by intersections between adjacent driving surfaces. 
     Referring to FIGS. 3 and 5, a tubular skirt 21 extends axially from fastener cam surface 13. Skirt 21 is flared at its outer end 22. The maximum external diameter of the skirt is at outer end 22. The skirt has a minimum external diameter in the region between surface 13 and end 22. 
     A first upper annular washer 23 has an inwardly directed flange 24 adjacent one end 25, and a bore 26 of a larger diameter below the flange. The innermost surface of flange 24 defines the minimum internal diameter of washer 23, and is slightly larger than the minimum external diameter of skirt 21. Thus, washer 23 is loosely held by skirt 20 to rotate freely thereon. 
     In assembling the fastener, washer 23 must be placed on skirt 21 before the outer end of the latter is flared out at end 22. The internal diameter of bore 26 is larger than flared end 22 in order not to interfere with rotation of the washer on the skirt. 
     In this embodiment, the overall axial length of washer 23 from the outermost points of end 25 to the outermost points of end 27 is greater than the length of the skirt from surface 13 to end 22, which keeps the skirt from scraping on a recessed workpiece 28 when nut 11 is threaded on a bolt or stud 30 to apply a load on workpiece 28. 
     Referring to FIGS. 4 and 11, surface 31 at the upper axial end 25 of washer 23 constitutes a cam surface with a first set of cam elements 32 spaced 60° apart, each comprising a sloping face 33 and an abutment face 34 shaped to match corresponding surfaces of the fastener cam elements 14. Thus, each of the abutment faces 34 extends substantially radially from the inner edge of flange 24. As a result, rotating nut 11 in the direction to apply a load to workpiece 28 causes each of the abutment surfaces 16 to drive the corresponding abutment face 34. If nut 11 alone is rotated in the opposite direction in an attempt to reduce the load on the workpiece, surfaces 15 slide up on surfaces 33 in a wedging action that locks the nut against any substantial rotation and even tends to increase the load on the workpiece. In order to avoid this wedging action, washer 23 must be turned simultaneously with nut 11. Washer 23 is therefore provided with a drive head 36 that can be gripped by a tool to turn the washer. Preferably, the drive head 36 has the same configuration and size as driving surfaces 18 on nut 11 with which it is juxtaposed, thus allowing a single tool to engage both drive head 36 and nut 11. 
     The assembly has a second annular washer 37 with a central aperture 38 of larger internal diameter than the external diameter of end 22 of the skirt. Washer 37 has an axial surface 39 that faces surface 41 of washer 23. In accordance with this invention, surfaces 39 and 41 are cam surfaces with cam elements 42 and 43, respectively. These cam elements have a height &#34;h&#34; that is not as high as the height &#34;H&#34; of cam elements 14 and 32. The height &#34;H&#34; for a nut having a distance of about 11/2&#34; between parallel surfaces 18 and intended to be used to mount truck tires is about 0.005&#34;, whereas the height &#34;h&#34; for the cam surfaces 39 and 41 (FIG. 11) is on the order of 0.001&#34;. 
     Another difference between the cam elements on cam surface 41, and the cam elements on the opposite surface is that the angle between adjacent cam elements 43 is substantially less than the angle between cam elements 32. The angle between adjacent cam elements 32 should be about three times as great as the angle between cam elements 43. Thus, there are about 18 cam elements 43, and the same number of cam elements 42, for an assembly having a hexagonal drive head. 
     A further difference between the configuration of cam elements 42 and 43, and cam elements 14 and 32 is that the slanting surfaces 44 of cam elements 43 slope in the reverse direction from the sloping faces 33 of cam elements 32. The slanting faces 45 of the cam elements 42, of course, slope in a direction such that the cam elements 42 fit snugly with cam elements 43. Cam elements 42 have slanting abutment faces 46 that slope in the opposite direction from surfaces 45. Cam elements 43 have corresponding slanting abutment surfaces 47 that slope in the opposite direction from surfaces 44. These relative directions of slope are such that surfaces 47 tend to drive the surfaces 46 when washer 23 is rotated in the direction to reduce the load applied to workpiece 28. However, the interaction between washers 23 and 37 improves the operation of the assembly in maintaining a high tensile load on the bolt or stud 30 and in allowing the assembly to be removed and reapplied many times. As nut 11 is rotated to tighten the fastener assembly, abutment surfaces 16 lock with abutment surfaces 34 to drive washer 23 therewith. Cam elements 43 ride up on cam elements 42 as nut 11 is tightened adding tensile stress to the bolt or stud 30, thereby increasing the tensioning effect of nut 11 on the stud or bolt 30. When nut 11 is rotated such as to loosen the fastener assembly, cam elements 42 and 43 ride down one another, releasing tensile stress, until abutment surfaces 46 and 47 lock and washer 37 rotates as a unit with washer 23. The release of tensile stress facilitates the removal of the fastener assembly. 
     The face 48 of washer 37 is annular and has a bearing surface 48A comprising a continuous annular spherical zone having a center of curvature lying on axis 19. Bearing surface 48A is formed to be self-centering in a concave annular seat 48B in the workpiece. Washer face 48, is relatively smooth so as not to score the surface of the workpiece. 
     The operation of the assembly is further substantially improved by a lubricating coating 55, such as a mixture of a dry film lubricant and phosphate, on the interface between the cam surfaces 39 and 41, although the assembly will work without that coating. The lubricant reduces the friction between washer 23 and washer 37. This allows washer 23 to slip over washer 37, permitting washer 37 to tend to remain stationary on the workpiece while nut 11 and washer 23 are being rotated to tighten the assembly. This further enhances the ability of the fastener to operate without scoring or galling the workpiece. 
     Washer 23, in this embodiment, is attached in axial alignment with nut 11 by the skirt and flared end 22. The second washer 37 is attached to the first washer by an annular clip 49 that engages the perimeter of an outwardly extending flange 50 at the end 27 of washer 23, and perimeter 51 of washer 37, which is substantially the same size as flange 50. 
     Clip 49 is in the form of a circular band having an axial length approximately the same as the combined axial lengths of the perimeters of washer 37 and flange 50. The clip is held in place by several tabs 52 that extend over the edge of the flange 50 and a collar 53 (FIG. 3) that extends over the edge of washer 37. In order to keep collar 53 from scraping the surface of the workpiece, the edge of the washer 37 has a small step 54 formed in it, the axial length of which is greater than the thickness of collar 53. 
     It will be understood by those skilled in the art that modifications may be made in the structure described herein without departing from the true scope of the invention.