MULTIPLE BELLEVILLE WASHER NUT CONSTRUCTION

Abstract: A nut (10) has a plurality of stacked Belleville washers (12, 14, 16, 18) held in unitary relation within a cage (20). One washer (16) is constructed of a material softer than that composing the other washers to provide a prevailing torque locking action. The nut is internally threaded (30) at an angle offset with respect to a plane (34) normal to the nut bore axis. In a use embodiment, a pressure washer (26) is mounted in a free-spinning manner in a cylindrical flange (22) of the cage (20).

Description: MULTIPLE BELLEVILLE WASHER NUT CONSTRUCTION BACKGROUND 1. Background of the Invention The present invention relates generally to nuts which have a plurality of washers or laminations forming the nut body and, more particularly, to such a nut which has the capability of being reused without sacrificing locking retention characteristics . 2. Description of Related Art Laminated nuts are known which include laminations or washers stacked together with a threaded opening common to each of the washers and unitarily secured within a cage. In use, the nuts are free running on a bolt until seated at which time when a locking load is applied by additional nut rotation, the various washers compress and flatten out establishing a mechanical thread interference via change of the hole size which serves to lock the nut to the bolt. An example of such prior art nuts are those set forth in U-S. patent 4,383,787, FREE SPINNING LAMINATED NUT WITH AUTOMATIC LOCK by Richard L. Reynolds. The patented nut although fully adequate for many purposes is not completely satisfactory on reuse in that it may suffer reduction of locking ability after even a single locking and release cycle. More particularly, if the nut is removed after once having been tightened down and locked onto a bolt consructed of relatively softer metal, the threads do not return to their original condition such that when reapplied to a bolt somewhat reduced locking action is experienced. SUMMARY OF THE INVENTION In accordance with the practice of the present invention, the reusability disadvantages of the prior art multiple washer nuts are minimized by the utilization of a combination of multiple washers arranged into a nut configuration having an offset thread. More particularly, a plurality of so-called Belleville washers are assembled or stacked onto one another within a suitable cage, such as a hexagonal cage. The threading of the nut bore is so formed as to be angularly canted or offset from the usual vertical arrangement of the threads to the nut bore longitudinal axis, which offset is in the same direction for each thread . When a nut of this invention is placed onto a bolt in tightened relation, the nut washers flatten out so that the threads on the bolt and on the nut flankingly contact each other in a locking manner. In this way, assuming removal prior to reuse, the individual washers can reassume a condition much closer to that of their original unstressed state increasing the prospects of achieving a renewed locking condition. This result is even further enhanced where the bolt material is softer than the nut washers (a not unusual condition) since the bolt threads do not have to be distorted as much with an offset nut thread to achieve a desired predetermined locking force. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational, partially sectional view of a caged multiple washer nut in accordance with the present invention; FIG. 2 is an end elevational view directed into the nut bore,- FIG. 3 is a side elevational, sectional view of FIG. 1; FIG. 4 is an enlarged sectional depiction of the threads of a laminated nut in accordance with this invention shown engaging corresponding threads on a bolt as in FIG. 3; FIG. 5 is a graphical depiction of acceptable threads on a nut of the present invention compared with a prior art nut on multiple installations; and FIG. 6 is a graph of the present invention peak off-torque compared with a prior known multiple washer nut. DESCRIPTION OF A PREFERRED EMBODIMENT For the ensuing description of the present invention, reference is now made particularly to FIGS. 1 and 2 where the multiple washer nut of the present invention is enumerated generally as 10. In its major elements, the nut 10 includes a plurality of Belleville washers 12, 14, 16 and 18 arranged in a stacked relationship within an outer cage 20 defining a generally unitary relationship. The outer edges of the washers and the general geometric configuration of the cage are such as to provide a nut of hexagonal cross- section. An edge portion of the cage material extends away from the washers in a direction generally parallel to the axis of the nut bore and partially turns back on itself to form a cylindrical flange 22 which is received within a central opening 24 of a pressure washer 26. The pressure washer opening has a diameter such as to be free-spinning with respect to the cage and washers of the nut proper. Before proceeding with the description of the more detailed aspects of the nut of this invention, it will be worthwhile to consider a proposed use of this nut in one of its more advantageous applications. In this application, the nut with pressure washer 26 is received on a bolt member and on being threaded therealong sufficiently, the washer 26 will apply a desired predetermined amount of force onto a receiving surface. When that force has been achieved the nut will have self-locked onto the bolt and remain that way irrespective of external vibrational or shock forces. One such apparatus requiring a nut as described would be a spindle nut for an automotive wheel drive, for example . As to detailed function of the described nut in this application, as the nut is advanced along the bolt and the washer 26 contacts a plate or other device against which the force is to be applied, the reaction force on the Belleville washers 12-18 tends to flatten them out and thereby effect locking of the nut to the bolt. The nut is then advanced in its forward motion until the predetermined force is exerted via the washer 26. At this time, the nut becomes locked via the interference between the nut threads and the bolt threads . Also, the washer 16 is a so-called prevailing torque washer in that it is constructed of a softer material than the other conical washers which causes it to direct an increased amount of restraining torque or locking torque onto the bolt than that of the other washers when the described nut is subjected to the predetermined load as it receives a bolt therein. Still further, it is a fundamental aspect of the present invention to provide a modified thread on the nut which is such as to produce an offset of the nut thread as compared to a receiving bolt thread serving to enhance the locking features of the nut as well as enable the nut to be reusable. Turning now to FIG. 4, there is shown in cross- section a threaded portion of the nut 10 of this invention enumerated as 30 with corresponding threaded portions of a bolt 32 on which the nut is received. For purposes of description, the bolt is depicted as having a 30-degree thread with the threads extending uniformly away from the bolt longitudinal axis . The threads on the nut, however, are each offset a preferred angle from a plane 34 normal to the nut bore axis . Best performance to date has been achieved with a nut having an offset of approximately 4 degrees. However, it is believed that some variation of the optimal value for this offset angle may be experienced depending upon the degree of out-of-flatness of the Belleville washers. In a frequent situation, the bolt is constructed of a softer material or one having a lower tensile strength than that of the nut. Assembly of the nut and bolt producing a clamp load results in some distortion of the bolt threads . As the described nut is tightened onto a bolt, when the nut Belleville washers are deflected approximately 4 degrees the nut thread flanks then match the bolt thread flanks which results in an overall less distortion of the bolt threads while retaining the required amount of locking force. Although the present invention has been described in connection with a preferred embodiment, it is to be understood that those skilled in the art may provide modifications which come within the spirit of the invention as described and within the ambit of the appended claims .

Claims: CLAIMS What is Claimed is : 1. A multiple washer nut including a plurality of conical washers nested in a stack with a common bore and a cage unitarily securing the washers together, said nut having a forward side which is first received on a threaded bolt for advancing therealong and a rear side, the improvement comprising: a continuous thread formed in the bore angularly offset with respect to a plane normally intersecting the bore central axis. 2. A multiple washer nut as in claim 1, in which the nut thread is offset toward the rear side. 3. A multiple washer nut as in claim l, in which the offset angle is such that as the conical washers flatten out during pressurized installation of the nut the nut thread flanks against the bolt thread. 4. A multiple washer nut as in claim 1, in which the amount of angular offset of the nut thread is substantially the same as the conicalness of the washers . 5. A multiple washer nut as in claim 1, in which one of the washers is constructed of a metal that is softer than the metal from which the other washers are constructed. 6. A reusable threaded nut assembly for advancing along a bolt to apply a predetermined amount of force against an object comprising: a plurality of Belleville washers nested together with a common bore; a cage encompassing the washers and retaining them as a unit, said unit having a forward side which leads as the nut assembly advances along the bolt to apply pressure; a generally semicylindrical flange integral with the cage on the forward side; a pressure washer having a central opening received within the semicylindrical flange, said washer being free-spinning within the flange; and a thread formed on walls forming the bore which is angularly offset away from the forward side an amount sufficient that the nut thread flanks with the bolt thread during pressurizing application of said pressure washer. 7. A reusable threaded nut as in claim 6, in which the nut thread is offset about 4 degrees. 8. A reusable threaded nut as in claim 6, in which one of the washers experiences an amount of interference force on pressurized threading along the bolt exceeding that of the other washers, and said one washer includes a bore opening with reduced cross- sectional portions than that of the other washers . 9. A reusable threaded nut as in claim 8, in which the one washer is constructed of a material softer than that of which the other washers are constructed. 10. A reusable threaded locking nut and washer combination for applying a predetermined amount of force against an object as the nut and washer advance along a bolt, comprising: a plurality Belleville washer nested together with a common bore, one of said washers being constructed of a metal softer than that from which the other washers are constructed; a cage with walls deformed about the washers to retain them as a unit, said cage having a forward side and a rear side; cage wall portions on the forward side forming a flange with a continuous radially outwardly facing opening; a pressure washer with a central opening received within the flange opening and so-dimensioned as to be free-spinning therein; and a thread formed in washer walls about the common bore offset an angular amount such when the nut and washer are advanced on the bolt to the point where the predetermined force is applied by the pressure washer the bolt and washer threads will generally flank against one another.

Inventors: MITTS RICHARD K, MITTS, RICHARD, K.
Applicants: MITTS RICHARD K, MITTS, RICHARD, K.
Application year: 1997
Main classification: F16B37
IPC codes: F16B39