Abstract:
A locking fastener assembly comprising a nut and a washer. The nut and washer each have opposed load bearing surfaces which include a series of annularly extending, slightly inclined faces forming shallow undulations around each surface. The load bearing surface on the nut is generally spherically convex and the load bearing surface on the washer is generally spherically concave. The nut rotates as it is installed while the washer is prevented from rotating so that the undulating bearing surface on the nut slides over the undulating bearing surface on the washer against ever increasing resistance until the assembly is properly seated and the nut is effectively prevented from counter-rotating by interference between opposed, inclined faces. A concave clamping surface is formed on the outer end of the washer on a radially extending flange. The flange flexes when the assembly is installed and resiliently urges the washer against the nut.

Description:
This is a continuation of application Ser. No. 09/933,312 filed Aug. 20, 2001 now U.S. Pat. No. 6,749,386 

   FIELD OF THE INVENTION 
   This invention relates generally to threaded fasteners. It relates particularly to locking fasteners of the type employing a threaded nut and a locking washer. 
   BACKGROUND OF THE INVENTION 
   A locking fastener or locking fastener assembly is employed to prevent loosening of a threaded fastener element in a fastener joint. There are numerous types of joints in which locking fasteners or fastener assemblies are not only desirable but necessary to prevent a nut from loosening. One such application is in the axle and wheel nut assembly of a motor vehicle or the like. 
   In a typical axle and wheel nut assembly, the hub is supported on a spindle by axle bearings which permit the hub, and thus a vehicle wheel, to rotate on the spindle. An axle bearing nut is threaded onto the free end of the spindle and holds the axle bearings and bearing races together in a predetermined relationship. The axle bearing nut must be set in precisely the proper position on the spindle to apply end loading on the bearing races sufficient to avoid excessive play in the bearings but insufficient to overload them, the result of either being possible bearing failure or even loss of a wheel. 
   Numerous types of nuts with positive locking components are well known. One of the oldest and most common of these is the conventional castellated nut and cotter pin assembly. The disadvantages of these assemblies are numerous. They include the necessity of carefully locating a hole through the axle spindle, of using an extra component, of reduced nut strength, of relatively long installation time and of the difficulties encountered in fine tuning the preload on the bearing races. 
   Newer developments in locking fastener assemblies include those found in the Anderson, Jr. U.S. Pat. No. 3,762,455, the Grube U.S. Pat. No. 4,812,094, the Burdick U.S. Pat. No. 5,533,849, and the Peterkort U.S. Pat. No. 5,597,278, for example. Of these, the Grube and Peterkort patents are assigned to the same assignee as the present invention, as will be noted. 
   The Peterkort patent discloses a locking fastener assembly consisting of a flanged nut and a retainer washer loosely seated on the nut&#39;s flange. The retainer washer includes a radially inwardly extending tab which is designed to slide axially along a slot in a threaded spindle while preventing the washer from rotating relative to the spindle. A releasable locking clip is positioned to lock the nut to the washer. The locking clip is released by engagement of a wrench socket with a hex-head on the nut so that the nut can be threaded to a desired bearing loading position. When the wrench is removed, the clip interlocks the washer and nut to prevent the nut from rotating. 
   The aforedescribed Peterkort locking fastener assembly is a highly effective device for use in vehicle wheel assemblies. It is simple and relatively inexpensive. However, its design focuses on limiting end play, not maintaining a constant pre-load. 
   Other known locking fastener designs include prevailing-torque locking fasteners. Locking action is achieved with frictional resistance induced between mating threads. There is positive resistance to assembly, which maintains throughout fastener seating and tightening. A high residual resistance to loosening remains even if fastener pre-load is lost. Disassembly is even difficult. Complete disengagement in service is highly unlikely. Prevailing-torque fasteners are generally all-metal fasteners with modified threads or fasteners with a separate non-metallic element or one fused to the threads. The former have fewer temperature and environmental limitations than the latter, but the latter do not encounter thread galling and other problems characteristic of the former. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an improved locking fastener assembly. 
   It is another object to provide a locking fastener assembly comprising only two components, a nut and a washer. 
   It is yet another object to provide a locking fastener assembly in which secure locking is achieved between a rotatable nut and a non-rotatable washer without the use of separate locking elements. 
   It is still another object to provide a locking fastener assembly including a new and improved locking mechanism. 
   It is a further object to provide a new and improved locking mechanism for a locking fastener assembly wherein a locking relationship is established directly between nut and washer. 
   It is yet a further object to provide a locking mechanism for a locking fastener assembly wherein a washer and nut interlock is established and a constant bearing load resiliently maintained when the assembly is employed to mount a vehicle wheel. 
   The foregoing and other objects of the invention are realized in a locking fastener assembly which comprises only a nut and a washer. Each is formed from medium carbon steel. 
   The washer includes a generally cylindrical washer body and a flange extending radially outward from the base of the body. A clamping surface is formed on the bottom of the flange and washer body base. 
   The top of the washer body has an annular, generally spherically concave load bearing surface formed on it. The load bearing surface includes an annularly extending series of inclined bearing faces forming a uniform undulation around the entire surface. A series of plateau surfaces between the inclined bearing faces form the upper peaks of the undulation. A series of valley surfaces between the inclined bearing faces form the valleys of the undulation. Each of the plateau and valley surfaces are spherically concave. Each of the inclined bearing faces is also spherically concave. The height of the plateau surface above the valley surface is slightly greater than the clearance between the threads in the nut and those on a vehicle axle spindle, for example, when the locking fastener assembly is in place. 
   The slightly concave washer body clamping surface on the bottom of the washer forms what approximates a shallow frustum of a cone. This surface is inclined upwardly from the outer periphery of the washer flange of its bottom toward the washer body axis. 
   The washer flange has a plurality of slots formed inwardly from its outer edge, at regular intervals around the flange. These slots permit intervening flange sections to resiliently flex, albeit only slightly, when the washer clamping surface is forced against an outer bearing race and is under the desired load. 
   An ear is formed inwardly of the base of the washer body, opposite the flange. The ear is designed to slide axially through a suitably formed slot in the threaded end section of an axle spindle to prevent the washer from rotating relative to the spindle as the nut is threaded onto this end section. In the alternative, a flat may be formed on the spindle and a corresponding flat formed inwardly of the washer body. 
   The nut includes a generally cylindrical nut body which is internally threaded. A hexagonal surface is formed around the periphery of the nut body to permit gripping the nut with a wrench. 
   Depending from the nut body is a unitarily formed annular skirt. The skirt is adapted to extend axially into the generally cylindrical body of the washer and then be formed outwardly under an undercut shoulder within the washer body to loosely, but securely, hold the washer and nut together. 
   The bottom of the nut body, above the skirt, has an annular, generally spherically convex load bearing surface formed on it. The load bearing surface includes an annularly extending series of inclined bearing faces forming a uniform undulation around the entire surface. A series of plateau surfaces between the inclined bearing faces form the lower peaks of the undulation. These plateau surfaces are spherically convex, with the same radius as the valley surfaces on the washer&#39;s load bearing surface. Each of the inclined bearing faces is also spherically convex, with the same radius as the bearing faces on the washer&#39;s nut bearing surface. 
   When the nut is threaded onto the axle spindle, the washer is pushed freely in front of it without rotating, until the slightly concave, frusto-conical clamping surfaces engage on the ends of the flange sections the inner bearing race of the outer bearing assembly supporting the wheel hub. Further axial travel of the washer is then resisted by the bearing race, first relatively lightly while the bearing races move closer together and then relatively firmly as the bearing races reach their operating positions. 
   Meanwhile, the peaks on the opposed undulating load bearing surfaces ride over each other with greater and greater difficulty as the load increases. Finally, they can slip past each other only when the flange sections on the washer begin to resiliently flex. The nut is then securely prevented from counter-rotating and loosening by the interlocking bearing faces and the resilient pressure of the washer. 
   In locked relationship, the spherically convex plateau surfaces in the load bearing surface of the nut seat flush against corresponding spherically concave valley surfaces in the load bearing surface of the washer. Also, the convex inclined leading bearing faces on the nut seat flush against the concave inclined trailing bearing faces of the washer and prevent the nut from backing off. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, including its construction and operation, is illustrated more or less diagrammatically in the drawings, in which: 
       FIG. 1  is an end view of a vehicle axle and wheel hub incorporating a locking fastener assembly embodying features of the present invention; 
       FIG. 2  is a sectional view taken along line  2 — 2  of  FIG. 1 ; 
       FIG. 3  is an exploded perspective view of a nut and washer in position to be assembled; 
       FIG. 4  is a bottom plan view of a locking washer assembly, partially in section; 
       FIG. 5  is a top plan view of a locking washer assembly, partially in section; 
       FIG. 6  is a side elevational view of a locking washer assembly, partially in section; 
       FIG. 7  is a plan view of a quarter segment of overlying opposed bearing surfaces on a nut and washer, showing their relationship to each other circumferentially; 
       FIG. 8  is an enlarged sectional view of an arcuate portion (on an 18° arc in the present illustration) of the mating bearing surfaces in the assembly, the view depicting curved bearing faces and surfaces as straight because of this; 
       FIG. 9  is a side elevational view of the nut, showing the convex curvature of its inclined bearing faces; and 
       FIG. 10  is a side sectional view through the washer, showing the concave curvature of its inclined bearing faces. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings, and particularly to  FIGS. 1 and 2 , an axle assembly for an automotive vehicle is shown generally at  10 . The axle assembly  10  includes a spindle  12  which extends horizontally from a vertically oriented plate  14 . The plate  14  forms the outer face of a fitting  16  which is mounted in a conventional manner on the frame (not shown) of a vehicle. 
   Seated for rotation on the spindle  12  is a wheel hub  20 . The wheel hub  20  includes a generally cylindrical body  22  formed unitarily with a radially extending flange  24 . A plurality of studs  26  extend axially from the flange  24  near its periphery. The studs  26  are employed in a conventional manner to mount a wheel (not shown) on the wheel hub  20 . 
   The wheel hub  20  is seated on the spindle  12  on an inner roller bearing assembly  28  and an outer roller bearing assembly  29 . The inner bearing assembly  28  is located on a cylindrical inner section  31  of the spindle  12  and is retained between a shoulder  33  on the spindle and an opposing shoulder  35  inside the body  22  of the wheel hub  20 . The outer bearing assembly  29  is located on a cylindrical outer section  37  of the spindle  12  and is seated against a shoulder  39  inside the hub body  22  and against a frusto-conical spacer  41  encircling the tapered mid-section  43  of the spindle on the inner end of the bearing assembly. 
   The outer bearing assembly  29  is held in operating relationship against the shoulder  39  and spacer  41  by a locking fastener assembly  50  embodying features of the present invention. In this regard, the locking fastener assembly  50  is threaded onto the threaded outer end section  45  of the spindle  12  and seats against the inner bearing race  47  of the bearing assembly  29 . 
   The locking fastener assembly  50  is threaded onto the end section  45  of the spindle  12  to take up undesired play in the bearing assemblies  28  and  29  and, accordingly, hold them both in proper operating position and relationship. If the fastener assembly  50  is threaded too snugly against the bearing race  47 , the bearing assemblies  28  and  29  will both be over-loaded and their operating life shortened. If the fastener assembly  50  is not threaded sufficiently far onto the end section  45 , the bearing assemblies  28  and  29  will have too much play and their operating life will be shortened. The locking fastener assembly  50  is designed to be turned onto the threaded end section  45  of the spindle  12  to a desired position and then held securely in that position by locking forces exerted internally of the assembly according to the invention. 
   Referring now to  FIGS. 3–10 , the locking fastener assembly  50  comprises only two components, a nut  52  and a retainer washer  54 . Both are forged steel elements. In the preferred embodiment shown here, the nut  52  is formed from medium carbon steel and then heat treated to an average hardness of  33  on the Rockwell C scale. The washer is also formed from medium carbon steel and then heat treated to an average hardness of  39  on the Rockwell C scale. 
   The nut  52  comprises a nut body  62  which is internally threaded at  64  for receipt of the threaded end section  45  of the spindle  12 . Externally, the nut body has a hexagonal shape surface  66  which is adapted to mate with a standard socket wrench for tightening and loosening the nut  52 . 
   Extending generally axially away from the nut body  62  at the inner end of the internal threads  64  is a skirt  68 . The skirt  68  extends away from the generally spherically convex load bearing surface  72  of the nut body  62  and through the retainer washer  54 . The skirt  68  is formed outwardly in a manner hereinafter discussed so that it retains the washer  54  on the nut  52  in loose relationship. 
   According to the invention, the generally spherically convex load bearing surface  72  on the nut body  62  is, in fact, an annularly undulating surface extending entirely around the nut body, as best seen in  FIG. 9 . The surface  72 , which will hereinafter be described in greater detail, may be formed using any desired technique but, in the present instance, is formed by cold forging using a die insert which is machined to the desired complex curvature shape using conventional ball end mill techniques. 
   The washer  54  comprises an annular washer body  82  having a generally spherically concave load bearing surface  84  at its inner end and a clamp surface  86  for engaging the aforedescribed inner bearing race  47  at its outer end. The clamp surface  86  is formed on the outer end face  88  of the body  82  and a washer flange  92  which encircles it. 
   The generally spherically concave load bearing surface  84  on the inner end of the washer body  82  is also an angularly undulating surface extending entirely around the washer body, as best seen in  FIG. 10 . The surface  84 , which will hereinafter be described in greater detail, is also formed by cold forging using a die pin which is machined on one end to the desired complex shape using conventional ball end mill techniques. 
   The outer end face  88  of the body  82  and flange  92  on the washer body  82  is slightly frusto-conical in shape. The end face  88  is inclined upwardly at an angle of approximately 3″ from the outer periphery  94  of the flange to the inner periphery  96  of the body  82 . 
   The flange  92 , which is approximately 0.12 inches (3.0 mm) thick in the washer  54  illustrated, is segmented by six cut-outs  98  around its circumference so as to define six radially extending flange sections  102 . The end face  88  is also interrupted by six Vee-shaped, depressions  104  extending radially inwardly from corresponding cut-outs  98 . This effectively separates the annular clamp surface  86  into six arcuate clamp surface segments  106 , the arcuate outer extremities of which, between cut-outs  98 , are able to resiliently flex axially of the washer  54 . Although the flange  92  is shown here separated into six flange sections  102 , however, it should be understood that the invention contemplates using a greater or lesser number depending upon the size of the washer and thickness of the flange. 
   Extending radially inwardly from the end face  88  is an ear  108 . The ear  108  is of a size and shape suitable to slide loosely in an axially elongated slot  49  formed on one side of the threaded end sections  45  of the spindle  12 . As will hereinafter be further discussed, when the fastener assembly  50  is installed, the ear  108  and slot  49  cooperate to prevent rotation of the washer  54  relative to the spindle  12 . Although the use of ear  108  and slot  49  cooperating to prevent washer  54  rotation is shown here in the context of vehicle hub  20  mounting, it should also be understood that the invention contemplates the use of other conventional means for preventing washer rotation. 
   Referring now in greater detail to the generally spherically convex load bearing surface  72  on the nut body  62 , it comprises a series of oppositely inclined side bearing faces,  73  with peaks in the form of plateau surface segments  74  and with narrow valley bottoms at lines  75 . Each pair of side bearing faces  73  with a valley floor line  75  between them forms what approximates an inverted Vee shape. 
   The plateau surface segments  74  are formed in the cold forging process so that they are all convex and lie on the surface of an imaginary sphere whose center is on the axis of the nut body  62 . In the nut  52  which is illustrated, and which has an outside diameter between flats of the hexagon of approximately 2.125 inches (54 mm) and a nut body  62  thickness of approximately 0.50 inches (12.7 mm), the radius of that sphere is 2.00 inches (50.8 mm). 
   Each inclined side bearing face  73  is also formed so that it is convex and is curved both radially and circumferentially of the nut body  62 . As will hereinafter be described, these convex surfaces  73  are formed so as to be complementary with corresponding concave side bearing faces in the generally spherically concave load bearing surface  84  on the washer body  82 . 
   In the nut body  62  illustrated, the height of each plateau surface segment  74  formed by adjacent side bearing faces  73 , i.e., the vertical height from the valley floor lines  75 , is 0.015 inches (0.38 mm). According to the invention, and for reasons hereinafter discussed, this height is slightly greater than the clearance between the threads on the end section  45  of the spindle  12  and the threads  64  in the nut body  62  when they are assembled. 
   Referring now in greater detail to the generally spherically concave load bearing surface  84  on the washer body  82 , the surface comprises a uniform series of inclined side bearing faces  116  with peaks in the form of plateau surfaces  118  and with wider valley floors in the form of valley surfaces  122 . Each pair of inclined bearing faces  116  with a valley surface  122  forms what approximates a Vee shape. 
   The valley floor surfaces  122  are formed in the forging process so that they are all concave and lie on the surface of an imaginary sphere whose center is on the axis of the washer body  82 . The radius of that sphere is 2.00 inches (50.8 mm). As such, it will be seen that the plateau surface segments  74  on the nut body  62  are perfectly complementary in shape to the valley floors  122  on the washer body  82 . 
   In the washer body  82  illustrated, the height of each plateau surface segment  118 , i.e., the vertical height from the valley floor  122 , is slightly less than 0.015 inches (0.38 mm). As a result, when nut  52  and washer  54  are seated against each other in nested relationship, each plateau surface segment  74  will seat uniformly on a corresponding valley floor  122  while opposed inclined bearing faces  73  and  116  will be slightly separated. 
   When the opposed bearing surfaces, surface  72  on the nut body  62  and surface  84  on the washer body  82 , are nested in locking relationship, however, the trailing inclined bearing faces  116  of the washer body  82  seat against the leading inclined bearing faces  73  on the nut body  62 . Because these opposed inclined bearing faces  73  and  116  are formed so as to be complementarily convex and concave, respectively, and all their radii of curvature axially of the assembly  50  and from its axis equal those of the aforementioned valley floor surfaces  122 , locking surface contact is maintained between them even if the nut  52  and washer  54  are not precisely parallel to each other because the nut does not thread perfectly squarely onto the spindle. 
   The nut  52  and washer  54  are assembled to create the locking fastener assembly  50  by inserting the skirt  68  of the nut through the washer in the manner best seen in  FIG. 6 . The skirt  69  is then dimpled outwardly by forming at six evenly spaced locations  69  around its periphery so as to underlie an annular inward projection  83  in the washer body and, accordingly, loosely but securely connect the nut  52  and washer  54  while permitting the nut to rotate freely relative to the washer. 
   In use for securing a wheel hub  20  on the spindle  12  in an axle assembly  10  for a truck or some other vehicle, for example, after a wheel hub  20  has been seated on its supporting bearing assemblies  28  and  29 , a fastener assembly  50  is slipped over the threaded end section  45  of the spindle  12  so that the ear  108  in the washer  54  slides along the slot  49  in the spindle until the internal threads  64  in the nut body  62  engage the external threads on the spindle. The nut  52  is then threaded onto the spindle  12  by hand until the clamp surface  86  on the washer body  82  engages the inner bearing race  47 . As the nut  52  rotates while being threaded onto the spindle  12  in this way, the washer  54  moves axially with it but is prevented from rotating because its ear  108  is axially slidable in, but rotationally fixed by, the slot  49  in the spindle. 
   As the nut  52  rotates, its undulating bearing surface  72  slips easily over the opposed undulating bearing surface  84  on the washer  54  as the nut pushes the washer before it. When the clamp surface  86  engages the inner bearing race  47 , however, further rotation of the nut is resisted with greater and greater effect by the interlocking effect of the opposed inclined side bearing faces on the nut  52  and washer  54 , respectively, as the nut turns and axial pressure builds up in the bearing assemblies  28  and  29 . As this pressure builds up, the flange sections  102  begin to flex, creating a resilient force tending to keep the inclined bearing faces of opposed side bearing surfaces  72  and  84  in interlocked relationship. 
   The flange sections  102  are designed to resiliently flex through an axial distance which is slightly greater than the clearance between the spindle  12  threads and nut body  62  threads. Because the flange sections  102  are able to flex slightly more than this clearance, the washer  54  can move axially under load to some degree without degradation of the lock between washer  54  and nut  52 . At the same time, because the height of the plateau surface  118  above the valley surface  122  in the washer body  82  is slightly greater than the clearance also, once a locking relationship is established with the proper preload the nut  52  and washer  54  can move slightly relative to each other without loosening the fastener assembly  50 . 
   When a predetermined torque setting is reached in turning the nut  52  of the locking assembly  50  onto the spindle  12 , the bearing assemblies  28  and  29  are properly preloaded. The locking assembly  50  can then be relied upon to resist all axial forces tending to cause the nut  52  to back off. Increased axial load from the wheel hub  20  merely causes the nut  52  and washer  54  to become more securely locked together against relatively rotation. Only by applying loosening torque to the nut  52  again, as with a hex wrench, can the locking assembly  50  be removed. 
   Although the invention in a locking fastener assembly has been described in the context of a vehicle wheel hub mounting arrangement, it should be understood that it might be otherwise employed. Its two-part simplicity, rugged construction, virtually fail-proof action and low manufacturing cost may make it very attractive in many applications. 
   While a preferred embodiment of the invention has been described, it should be understood that the invention is not so limited, and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.