Patent Publication Number: US-9423200-B1

Title: Virtual preloaded bearing

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described was made in the performance of official duties by one or more employees of the Department of the Navy, and thus, the invention herein may be manufactured, used or licensed by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND 
     The invention relates generally to bearings for gun-mounts for shock absorption. In particular, the invention relates to a circumferential array of bearings, preloaded in a gun-mount to absorb recoil, thereby distributing stresses on the gun-mount and reducing overall mount deflection. 
     Conventional techniques for handling large radial loads involve tapered roller bearings. For example, hubs on automobile wheels use tapered roller bearings to withstand the radial load of such a motor vehicle traveling along a road. Other applications that experience a comparably slower spin rate, such as gun mounts, often employ the use of shims between a mount base and rotating yoke base. As a gun recoils, the radial load transmits through the yoke base into the central azimuth bearing and shims into the mount base. 
     A disadvantage to this configuration is that the shims do not permit a very stiff joint. As a result, rocking between the shim and the mount base is evident and can lead to high wear rates. One obvious solution involves drastically increasing the size of the azimuthal bearing to minimize deflection from the radial gun fire loads. However, this approach also imposes severe weight and manufacturing constraints. 
     Conventional techniques for detecting fatigue defects in gun and mortar mounts include inspection of the system after a given number of firings, with mean time between failure being calculated theoretically. With the advent of finite element analysis, theoretical computation of fatigue and mean times between failures has greatly improved. However, due to the complexity of some systems, empirical data provides a more accurate determination of fatigue life. 
     Outside of gun and mortar mounts, empirical fatigue testing has been conducted for over half a century. This has been limited to material samples, consisting of varying materials, tempers, and environmental conditions. Recently with the increased capability of servo motors and computer control, entire mechanical systems have undergone system level fatigue testing. 
     SUMMARY 
     Conventional load bearing systems yield disadvantages addressed by various exemplary embodiments of the present invention. In particular, a preload bearing is provided for mounting into an orifice in a shock-inducing platform. The bearing includes a cylindrical housing insertable into the orifice of the platform with a housing axis oriented vertically in relation to the platform, the housing having a closed bottom end and an open top end; a scraper that attaches to the bottom end of the housing for receiving compressive load from underneath; a crown roller disposed to extend radially from the housing; a shaft coaxial with the crown roller disposed within the housing along a roller axis perpendicular to the housing axis; and a cap that covers the open top end of the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and various other features and aspects of various exemplary embodiments will be readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, in which like or similar numbers are used throughout, and in which: 
         FIG. 1  is a isometric view of a load mount; 
         FIG. 2  is an elevation cross-section view of an exemplary preloaded bearing; 
         FIG. 3  is an isometric exploded view of the preloaded bearing; 
         FIG. 4  is an elevation cross-section view of a conventional load mount featuring a central bearing; 
         FIG. 5  is a first elevation cross-section view of the exemplary load mount with preloaded bearings; 
         FIG. 6  is a second elevation cross-section view of the exemplary load mount with preloaded bearings; and 
         FIG. 7  is an elevation cross-section view of the load mount. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
     Exemplary embodiments described herein provide a trainable gun-mount with increased stiffness as compared to conventional designs, thereby improving weapon accuracy. Additional advantages include improving load dispersion throughout and maintainability of the trainable gun-mount, as well as decrease the gun-mount&#39;s weight. Accordingly, the gun-mount includes a yoke base affixed to a central bearing. The yoke base includes a pair of trunnions from which gunfire recoil force imparts into uprights of the yoke. 
     In these embodiments, a series of roller bearing assemblies with crowned rollers are circumferentially mounted to the yoke base equidistant from the central bearing. These roller bearing assemblies are installed from the top of the yoke base to aid in maintenance. After installation, axial loads imposed on the roller bearing assemblies impart a preload between the yoke base and the mount base while they remain affixed via the central bearing, thereby improving load distribution. Stiffness substantially increases between the yoke base and the mount base as compared to conventional designs, thereby improving gunfire accuracy. 
     The purpose of these embodiments is to minimize deflection and weight in a bearing assembly that experiences transient radial loads, such as impulse shocks. This is accomplished by redistributing radial loads imparted on a central bearing across concentrically mounted roller bearing devices that are preloaded after installation, thereby increasing the overall stiffness of the assembly. The radial loads are dispersed across a larger area of contact thus lowering the load requirement of the central bearing, increasing stiffness of the assembly and decreasing overall system weight as compared to a single larger bearing of equivalent stiffness. 
     Thus a simple light weight design is desired to disperse the radial load from the central bearing while increasing stiffness and decreasing weight. Additional benefits from this design include simplified maintenance, as the roller bearing devices have ready accessibility for removal and do not require complete disassembly of the gun-mount system. The resulting design is the virtual preloaded bearing; named “virtual” for replacing a much larger single bearing with a central bearing and a distributed series of smaller roller bearing devices that provide the same functionality. The exemplary design provides the distinct advantage over previous designs of being lighter, stiffer and easier to maintain. By contrast, larger bearings of equivalent stiffness are costly and heavy, and shims provide poor stiffness to the assembly, as well as being difficult to replace and maintain. 
       FIG. 1  shows an isometric assembly view  100  of a mount base  110  for gun or mortar. A mount base  110  has a pair of mount plates  120  on a flat platform  130  that flank a gun yoke base  140  therebetween. The plates  120  support parallel yoke upright arms  150 . The platform  130  defines axial (X) and lateral (Y) directions, and is perpendicular to the vertical (Z) direction. The yoke base  140  includes a central bearing  160  in a turret well for disposing the gun (not shown). 
     Force load is applied to a pair of trunnions  170  disposed on each yoke upright arm  150 . The trunnions  170  are incorporated within horizontal bearings  175 . The platform  130  includes a pair of exemplary virtual preloaded bearing devices  180 . The central bearing  160  pivots in pitch, i.e., rotating in the lateral (Y) axis. In addition, each yoke upright arm  150  includes an exemplary bearing device  180  attached by a bracket  190 . The bearing devices  180  are substantially equidistant from the center of the central bearing  160  to more ideally distribute preload forces, whether disposed on the yoke base  140  or in the brackets  190 . 
       FIG. 2  shows an elevation cross-section assembly view  200  of an exemplary configuration for the preloaded roller bearing device  180 . A sealed crown roller bearing  210  fits onto a cylindrical shaft  220 . These bearings  210  press into two corresponding holes of a yoke  230 . This sub-assembly fits into a housing  240  having an attachment lip  245  at its top. A pair of threaded caps  250  double nut the yoke  230  inside the housing  240  and provide the necessary torque via the drive socket located on top of the caps  250 . The housing  240  attaches to the mount base  110  by screws  260  that pass through the lip  245 . A scraper  270  fixes to the bottom of the housing  240  with screws  280 . The scraper  270  clears the contact surface of the platform  130  for the crowned roller bearing  210 . 
       FIG. 3  shows an isometric exploded view  300  of exemplary bearing components  310 . The yoke  230  includes a first opening  320  for receiving the shaft  220  and a second opening  330  for receiving an alignment pin  340  for insertion therein. The common axis of the shaft  220  and yoke  230  through the first opening  320  is perpendicular to the longitudinal axis of the housing  240 . The pin  340  aligns the yoke  230  in the second opening  330  of the housing  240 . The concatenated caps  250  cover the open top of the housing  240  within the lip  245 , and the scraper  270  attaches at the bottom of the housing  240 . 
       FIG. 4  shows an elevation cross-sectional view  400  of a conventional mount base  110  with load distribution. The central bearing  160  in the yoke base  140  is shown disposed on the mount base  110  supported on proximal and distal bolts  410 . A first vertical gap δ x1    420  represents the distance between the flat platform  120  and the yoke base  140 . A bolt preload force  430  in the vertical (Z) direction at the proximal bolt  610  secures the yoke base  140  to the mount base  110 . A recoil force  440  applied at the trunnions  170  induces a recoil moment  450  through the yoke upright arm  150 . The recoil force operates substantially in the axial (X) direction, with the recoil moment induces pitch motion involving the recoil force operating a vertical (Z) distance between the trunnions  170  and the platform  120 . A total force  460  at the distal bolt includes the preload and recoil forces. The distal bolt  410  also receives horizontal force  470  in the axial (X) direction. 
       FIG. 5  shows an elevation cross-sectional view  500  of a mount base  110  with a preload installation flange  510  that includes one of the roller bearing devices  180  in the yoke base  140 . A second vertical gap δ x2    520  denotes the vertical distance between the flat platform  120  and the mount base  110 . The second vertical gap  520  is smaller than the first vertical gap  430 . The mount base  110  provides a first exemplary load distribution with the roller bearing devices  180  on the yoke base  140 . The proximal and distal bolts  410  receive respective (and equivalent) preload forces  430 . A bolt in the installation flange  510  receives a total force  530  from the preload and recoil forces. 
       FIG. 6  shows an elevation cross-sectional view  600  of the mount base  110  with a second exemplary load distribution with the roller bearing devices  180 . A mounting assembly  610  on each yoke upright arm  150  includes the bracket  190  and its associated roller bearing device  180 . A third vertical gap δ x3    620  represents the distance between the flat platform  120  and the yoke base  140 . The third vertical gap  620  is larger than the second vertical gap  520 . 
     The preload forces  430  are applied to the bolts  410 . An additional load  630  is applied to the roller bearing device  180  at the installation  510 . A counter-recoil force  640  on is applied to the trunnions  170  to produce a counter-moment  650 . This produces a compensating load  660  at the mounting assembly  610 . These combined counter recoil reaction forces  630  and  660  compensate for the forces transmitted by applied counter-recoil force  640  and thereby reduce rocking motions on such mounting systems. 
       FIG. 7  shows an elevation view  700  of the yoke upright arm  150  from a bilateral midline between the span of the loading rod (not shown) along the lateral (Y) direction. The central bearing  160  and the roller bearing device  180  at the installation  510  are also shown. The roller bearing devices  180  are located substantially equidistant from the central bearing  160 . The yoke base  140  connects the loading rod (not shown) to the mount base  110 . The exemplary bearing devices  180  are torqued inducing a preload between the mount base  110  and the yoke base  140 ; thereby preventing loss of contact between the roller bearing devices  180  and the mount base  110  during radial loading force  640  at the trunnions  170 . 
     The Virtual Preloaded Bearing Assembly is applicable to any situation involving a bearing with a high radial load and low revolutions per minute. This setup reduces overall system weight while maintaining equivalent stiffness response. Obvious applications include gun mounts. 
     The exemplary design was conceived for use on the Dragon Fire 105 mm Trainable Gun Mount (TGM) Demonstration Program for the U.S. Air Force to reduce deflection in the mount and simultaneously reducing weight. This design has immediate use for the Ghostrider AC-130J and Stinger II AC-130W Gunship 105 mm TGMs and can be retrofitted on the 30 mm TGM to increase stiffness. The Virtual Preloaded Bearing has utility not only on gun mounts but on all other applications involving bearings experiencing radial load and low revolutions-per-minute in which stiffness and weight are of concern. 
     While certain features of the embodiments of the invention have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments.