Self-locking fastener with captive washer

Abstract: This invention relates to a wedge-locking fastener assembly (10) in which a washer (34) is connected to flanged nut (20) by a series of tabs (40) that extend around the outer edge of the flange (32) on a nut (20).

Description: This application refers to a self-tightening fastener according to the first part of claim 1. Background of the Invention Self-tightening fastener assemblies having cammed wedge locking surfaces are known in the art. The fastener assembly described in this application includes a nut and a washer having confronting cammed faces. It is desirable to captively retain the washer on the nut to facilitate fastening the fastener on a workpiece. An example of a self-tightening fastener of the above-mentioned type including a retainer may be found in US-A-5 203 656 which uses an annular retainer that is a separate component with respect to the nut and the washer. Another nut having a captively-retained washer is disclosed in European Patent Specification No. 0350711, in which the nut has a flared section that is received inside the washer opening. Another variation of this product is illustrated in US-A-5 626 449 in which the nut has an internal flared section that is received inside the center opening of a complementary washer. Summary of the Invention The broad purpose of the present invention is to provide an improved wedge locking fastener having a captively retained washer. This object is achieved by a self-tightening fastener according to claim 1. In the preferred embodiment of the invention, a cup-shaped washer has an integral annular cylindrical skirt that extends around the outer edge of the flange. Tabs extend radially inwardly from the periphery of the skirt around the flange of the nut. The arrangement is such that the washer can move axially as well as rotatably with respect to the nut to permit the wedge-locking cams to wedge the nut between the cams on the washer and the threads on the bolt. When the nut is turned in a tightening direction, it tightens the washer on the workpiece. When the nut tends to rotate in the loosening direction, such as in response to vibration, the washer remains fixed, but the nut becomes tighter in the manner described in my prior patents. Another embodiment of the invention employs a pair of washers. The first washer adjacent the nut has a cam surface engaging the nut and a flat bottom surface. The second washer has a cup-shaped configuration and encloses the first washer with tabs that engage the flange of the nut. This embodiment is easier to manufacture than the other embodiment because it employs a conventional washer that is disclosed in my U.S. Patent No. 5 080 545. Still further objects and advantages of the invention will become apparent to those skilled in the art to which the invention pertains upon reference to the following detailed description. Description of the Drawings The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which: FIGURE 1 is a perspective view of a nut with a captive cup-shaped washer illustrating the preferred embodiment of the invention; FIGURE 2 is a sectional view taken through a fastener assembly constructed according to the invention for securing two workpieces together; FIGURE 3 is a view taken in the same direction as Figure 2, but showing the nut and washer combination in side elevation; FIGURE 4 is an enlarged view of the interior of the washer to show the camming faces; FIGURE 5 is an enlarged bottom view of the bottom of the nut to show the camming faces; FIGURE 6 is an enlarged view of a section of a typical cam profile; and FIGURE 7 illustrates another embodiment of the invention in which the cup-shaped washer and the internal washer are separate components. Description of the Preferred Embodiment Figure 1 shows a fastener assembly 10 illustrating the preferred embodiment of the Invention. Figures 2 and 3 show fastener assembly 10 mounted on a steel bolt 12 having a threaded shank extending through two workpieces 14 and 16. The bolt has a conventional button-shaped head 18 to prevent the head from being gripped by a wrench or pliers. A steel nut 20 has an internal threaded surface 22 meshed with a continuous helical thread 24 on bolt shank 26. The nut is fastened on the bolt by a wrench, not shown, engaging a multi-sided head 28. Preferably head 28 has six flat sided surfaces arranged in the conventional hexagonal configuration. The nut has an end camming face 30 forged with an integral annular flange 32. Flange 32 has a diameter larger than the maximum diameter of the nut head. Consequently, the circular bottom face of the flange has a substantially larger surface area than the hexagonal cross section of the nut head. A steel, non-flexing washer 34 is captively mounted on the nut. The washer has a generally planar lower face 36 connected to an integral annular skirt 38 which extends toward the nut and around flange 32. The upper edge of the skirt has a plurality of retaining tabs 40 that are bent radially inwardly toward the nut head and above the top of the flange as illustrated in Figure 2. The tabs are equi-angularly spaced and permit the nut flange to rotate within the washer skirt, and permit a sufficient axial motion with respect to the washer so the camming faces on the nut and the washer can slide to provide the wedge-locking action. The work-engaging face of washer at 44 is flat and devoid of any obstruction, so that it can slide on the workpiece. The inside surface of the washer has a camming face 45 as best shown in Figure 4. The washer also has a central non-threaded opening 46 for receiving the threaded bolt shank. Both nut camming face 30 and washer camming face 45 each have twelve camming structures. Each camming structure comprises a ramp 48 and a shoulder 50. The ramps and shoulders are identical, however, arranged in such a manner that when the nut is turned in a turning direction, the shoulders on the nut push the shoulders on the washer as the nut becomes tightened with the washer on the bolt. A typical camming ramp and shoulder are illustrated in Figure 6. The slope angle 52 of the shoulder is about 40°. The term "slope angle" designates the angle that shoulder 50 makes with respect to an imaginary radial plane 54 extending normal to nut turning axis 42. The slope angle 56 of each ramp is about 8°. The shoulders and the ramps of each camming surface are connected so that each camming face has a continuous uninterrupted undulating contour. The fastener can also function with a single ramp and shoulder on the camming faces of the nut and the washer or a greater number than shown in Figures 4 and 5. Nut 20 is threaded on shank 26 of the bolt by rotating the nut in the clockwise direction when viewing the top of the nut. During the nut tightening operation, the bottom flat face of the washer becomes frictionally anchored to the surface of workpiece 14. Further rotation of the nut In the same direction causes the cam shoulders on the nut to push the cam shoulders on the washer until the nut is fully tightened, applying a tensile stress on the bolt shank. When the nut is rotated In the opposite or loosening direction, either by friction or deliberately, the cam ramps on the nut tend to slide up the cam ramps on the washer. The nut thus moves to a wedged, locked position between the washer ramps and the threads on shank 26. The lock action is enhanced by the fact that the axial thickness dimensions of the shoulders is less than the thread pitch distance of the threads on shank 26. Figure 7 shows another embodiment of the invention in which another self-tightening fastener 100 employs the same nut, bolt and workpiece as is illustrated in the embodiment of Figure 2. However, this embodiment of the invention employs a relatively flat washer 102 and a cup-shaped washer 104. Flat washer 102 is similar to the washer illustrated in my prior Patent No. 5,080,545 including an upper cam face 106 which is generally identical to the inside face of the cup-shaped washer of Figure 1. Cam face 106 is engageable and complementary with the camming face 30 of the flanged nut. Bottom surface 108 of the washer is flat. The washer also has an inner opening 110 which is aligned with the central threaded opening of the nut. Cup-shaped washer 104 is substantially identical to the cup-shaped washer of Figure 1 including a flat work-engaging surface 109 and a central opening 110aligned with the central opening of flat washer 102. Cup-shaped washer 104 has a cylindrical periphery 112 which encloses the flat washer, and extends upwardly. The upper edge of periphery 112 has a plurality of equi-angularly spaced retaining tab means 114 which wrap around the flange of the nut. Periphery 112 of the cup-shaped washer locks the edge of the flat washer while tab means 114 permit the cup-shaped washer to rotate on the bolt shank and to move axially along the bolt to provide the wedge-locking action. The embodiment of Figure 7 is similar to the embodiment of Figure 2 except that the cam means on the washer are on a separate washer instead of being integrally formed with the cup-shaped washer. The tightening and loosening functions are the same as the embodiment of Figure 2.

Claims: A self-tightening fastener for co-acting with a threaded stud or bolt (12) to apply a tightening force to a workpiece (14, 16), comprising: a nut having a central opening with internal threads (22) disposed about a turning axis, the nut (20) having a multi-sided head (28) for engaging a turning tool for applying tensile stress to said stud or bolt (12) when tightened thereon, and an annular flange (32) with a peripheral edge, a non-flexing annular member (34) having a non-threaded central opening aligned with the central opening of the nut (20), means forming a first cam surface (30) on the flange (32) of the nut (20) and means forming a second cam surface (45) on said annular member (34), the second cam surface (45) engaging said first cam surface (30) for driving both said nut (20) and said annular member (34) when the nut (20) is tightened in a turning direction about said turning axis on said stud or bolt (12), and for locking said nut (20) on said stud or bolt (12) when the nut (20) is rotated on the stud or bolt (12) with respect to the annular member (34) in the opposite direction about said turning axis; means for connecting the nut (20) to the annular member (34) to prevent separation thereof but permitting both limited relative axial motion and relative rotational motion of the nut (20) with respect to the annular member (34), characterized in that said annular flange (32) is an integral part of the nut (20) and that said annular member (34) includes a flat radial wall axially aligned with said flange (32), a continuous annular skirt (38) extending axially from said radial wall beyond said flange (32), and plural tabs (40) extending inwardly from said skirt (38) to overly said flange (32) and prevent the nut (20) from separating from the annular member (34). A fastener as defined in claim 1, in which the first and second cam surfaces (30, 45) each has a sloping cam ramp (48) and a cam shoulder (50), the sloping face of the ramp (48) on the second cam face (45) sloping in the opposite direction as the sloping face of the ramp (48) of the first cam face (30). A fastener as defined in claim 1 or 2, in which the annular member (34) has an inner surface with said means forming the second cam surface (45) comprising integral cam structures formed on said inner surface, and a flat work-engaging outer face (44). A fastener as defined in any one of claims 1 to 3, in which the multi-sided head (28) has six flat sides. A fastener as defined in any one of claims 1 to 4, in which the first and the second cam surfaces (30, 45) are axially aligned when placed on a stud or bolt (12). A fastener as defined in claim 1, characterized in that said means forming the second cam surface (106) comprises a separate annular disc (102) seated between the nut (20) and the radial wall of the annular member (104). A self-tightening fastener assembly (10) comprising: an elongated, externally threaded stud or bolt (12); and a self-tightening fastener according to any one of claims 1 to 6.

Inventors: MCKINLAY ALISTAIR N, MCKINLAY, ALISTAIR N.
Applicants: HONG KONG DISC LOCK CO, HONG KONG DISC LOCK COMPANY LTD.
Application year: 1997
Main classification: F16B39
IPC codes: F16B39