Patent Grant
9423200
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.
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.
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:
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'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.
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.
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.
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.
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.
| Number | Name | Date | Kind |
|---|---|---|---|
| 515018 | Rapieff | Feb 1894 | A |
| 2396247 | Chadwick | Mar 1946 | A |
| 2410614 | Trotter | Nov 1946 | A |
| 4967640 | Dodd | Nov 1990 | A |
| 6276260 | Bianchi | Aug 2001 | B1 |
