Ordnance – Mounts – With recoil check
Reexamination Certificate
2002-02-22
2004-02-24
Johnson, Stephen M. (Department: 3641)
Ordnance
Mounts
With recoil check
Reexamination Certificate
active
06694856
ABSTRACT:
BACKGROUND OF THE INVENTION
Many devices, such as turreted artillery, aircraft landing gear, various kinds of reciprocating machinery, vehicle shock absorbers and struts, seismic event attenuation devices, etc., undergo or isolate severe impulse loading, that is high loading over very short durations. Proper handling of these loading conditions typically is essential to the survival, if not the proper functioning of the device. For example, the accuracy of stabilized turreted, rapid-fire gun systems is limited by the structural flexibility of the gun barrel and the gun mounting structure. To improve the accuracy of sustained rounds, high frequency recoil forces that excite the structural dynamics of the turret must be dissipated. Although artillery applications are referred to prominently herein, the principles and embodiments of the invention described below apply to any application with respect to which severe impulse loading is of concern.
Referring to
FIG. 1
, some high-caliber, rapid-fire guns G employ damping systems D to damp recoil forces transmitted to the gun mounting structure, or fork F, along a direction T that is generally aligned with gun trajectory. Typically, damping systems D rely on passive dampers.
As shown in
FIG. 2
, a passive damper
10
typically includes a cylinder
15
, having a chamber that contains a working fluid. A piston
25
has a head
30
, received in chamber
20
, and a piston rod
35
extending from head
30
and through an aperture
40
in cylinder
15
. The head
30
is moveable within the cylinder between ends
31
and
32
, and typically has apertures or valves (not shown) that pass working fluid as head
30
moves against the working fluid. Alternatively, head
30
and chamber
20
may define a narrow passage (not shown) through which the working fluid passes.
Cylinder
15
defines a first eye
45
, or other mounting convention, for installation to fork F. Piston rod
35
terminates in a second eye
50
, or other mounting convention, for installation to gun G. A first spring retainer
55
, connected to cylinder
15
, and a second spring retainer
60
, connected to piston rod
35
, retain a recoil spring (not shown in
FIG. 2
, but see recoil spring
165
in
FIG. 6
) that biases piston
30
relative to cylinder
15
into a battery position.
When gun G discharges, gun G recoils with a force that urges piston
30
and cylinder
15
to translate relatively, against a restoring force of the recoil spring
62
and the viscous force of the working fluid against which piston
30
works. As piston
30
works against the working fluid, the working fluid becomes heated in an amount corresponding to the work. Thus, the energy associated with a recoil force is converted into or dissipated in the form of heat.
Energy dissipation directly corresponds to the viscosity of the working fluid. Viscosity is a measure of the resistence of fluid to angular deformation. That is, as viscosity or fluid resistence increases, the amount of work which a piston must undertake to move relative to the associated cylinder increases. Increasing the work that the piston exerts against the fluid increases the heat content or temperature of the fluid. The amount of heat generated and dispersed by the working fluid directly corresponds to the amount of recoil energy dissipated. In other words, increasing the viscosity of the working fluid which, during recoil, causes the piston to generate more heat in the working fluid, results in dissipating more energy of the recoil.
If the amount of energy a damper dissipates is too little, gun G recoils against forks F with an impact that can distort the forks F, adversely effecting gun accuracy, and can damage the forks F, associated electronics and other non-isolated physical structures. Large loads not damped, but transferred to, for example, the frame of a helicopter or other mobile gun transport, also will adversely impact transport handling properties or render the transport unstable or uncontrollable. If the amount of energy dissipated is too much, the gun recoil may be insufficient to compress the recoil spring, which in turn may prevent the gun from returning to the battery position. If gun G does not return to the battery position, gun G may not be able to expel spent cartridges, receive a new round or may experience other failures. Accordingly, energy dissipation must be carefully managed or predicted so that gun G is more accurate and does not prematurely breakdown due to inadequate recoil energy dissipation, or fail due to overly aggressive energy dissipation.
Passive dampers can not adequately damp guns because the amount of energy which passive dampers dissipate generally remains constant, whereas the recoil energy varies. A typical passive damper employs a working fluid that has a generally fixed or predictable viscosity. Fixed viscosity results in generally constant energy dissipation. Accordingly, a working fluid selected for a passive damper may be appropriate for damping a minimum anticipated recoil energy. In order to ensure that a recoil spring returns a gun to battery position. The amount of damping provided in such arrangements generally falls well short of most recoils realized. Consequently, less than an optimal amount of recoil energy is dissipated by the fluid. On the other hand, the amount of recoil energy realized varies according to factors such as round temperature, age, production facility, etc. Consequently, guns and gun mounts experience higher recoil forces than necessary, which introduces structural instabilities that adversely impacts accuracy. Guns and gun mounts also wear much faster than if equipped with more effective damping.
Although not in the context of artillery, dampers exist that provide for varying damping. Some variable dampers include actuated valves for controlling, thereby impacting effective damping, of the damper. However, these dampers rely on moving components to adjust damping, which is cumbersome and not readily adaptable to rapid extreme impulse loads.
Other variable dampers eliminate the mechanical viscosity control components by utilizing active working fluids having viscous properties that change under the influence of electric or magnetic fields. Active fluids, such as Magnetorheological (MR) and Electrorheological (ER) fluids, have the unique ability to change properties when electric or magnetic fields are applied thereacross, respectively. This change mainly is manifested as a substantial increase in the dynamic yield stress, or apparent viscosity, of the fluid.
MR fluids are preferred because of their superior performance. For example, as compared to ER fluids, MR fluids possess an order of magnitude higher yield stress and a much wider operating temperature range. Specifically, the COTS MR fluid, VersaFlo™ by the Lord Corporation, is far less sensitive to contaminants than ER fluids and can be operated in a temperature range from −40 to 150 degrees Celsius. A key advantage of MR fluids is that they require activation voltages of less than 100 volts, an order of magnitude less than ER fluids. This low-voltage operation capability is particularly attractive where heavy power amplifiers cannot be accommodated. In summary, the advantages of MR fluids derive from their ability to provide robust, rapid response interfaces between electronics controls and mechanical systems in real time.
MR devices, such as rotary brakes and linear displacement dampers have been commercialized. However, while the overall use of MR fluid in these devices has increased, both in terms of effectiveness and creativity, the analytical modeling and systematic design aspects have lagged. To a large extent, this can be attributed to the complex phenomenological behavior of these fluids.
MR fluids exhibit nonlinear effects due to applied field, applied load, strain amplitude, and frequency of excitation in dynamic displacement conditions.
FIG. 3A
is a schematic drawing of the COTS Lord Rheonetics™ damper, white
FIG. 3B
shows representative test data obtained from this device. The plots
Chen Peter C.
Wereley Norman
Johnson Stephen M.
The University of Maryland
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