GUN PIPE OSCILLATION DAMPER

Abstract: A damping device for a gun pipe (1) having a muzzle brake (2) comprises a recoil brake (3) and an oscillation damper (9) to prevent natural oscillations in the gun pipe when firing a shot, from propagation to the recoil brake. The connection of the oscillation damper to the recoil brake (3) and the gun pipe breeching (5) is such that the force transfer coupling between the breeching and the recoil brake is reduced with respect to said natural oscillations. The oscillation damper (9), which may take the form of a column of Belleville springs (10), is dimensioned so that the damping device as a whole has a rigidity substantially less than the recoil brake alone and forms an oscillatory system with a natural frequency substantially lower than the frequency of said natural oscillations of the gun pipe, when firing a shot.

Description: Gun Pipe Oscillation Damper Technical Field Present invention relates to an elastic oscillation damper to prevent natural oscillations which, when firing a shot, arise in a gun pipe having a muzzle brake, from propagation to a recoil brake for the gun pipe. The invention also concerns a damping device for a gun pipe with a muzzle brake, comprising a recoil brake and said oscillation damper. Background Art It is known to provide a gun with one or more damping devices to give the recoiling parts of the gun a controlled deceleration when firing a shot. Guns of a larger caliber are in addition often provided with a muzzle brake mounted at the muzzle end of the gun pipe, serving to reverse the direction of a part of the gas flowing out behind a launched shell and thus absorb a part of the recoil forces. However, when a projectile leaves the gun pipe, the pressure of gas against the muzzle brake causes the pipe to be stretched in its longitudinal direction and the pipe is then brought into longitudinal natural oscillations. These natural oscil¬ lations, having a frequency depending directly on the geo¬ metric design of the gun pipe and the material from which the pipe is made, are transferred to the recoil brake of the gun. Measurements have shown that the natural oscillations of a gun pipe may cause the momentary value of the force supplied to the recoil brake to vary nearly ± 100 % about an average value, which corresponds substantially to the recoil force from the shell discharge itself. As a result, the maximum material tensions are also increased accordingly. When exposed to a combination of oscillating force strain and high material tensions, the risk of material fatigue is always present. Hence- an object of the present invention is to provide an elastic oscillation damper for a damping device of the type initially described, to appreciably prevent the natural oscillations of the gun pipe from propagation to the recoil brake of the gun, when firing a shot. Disclosure of Invention The invention concerns an elastic oscillation damper of the type initially described, being designed to be connected to the recoil brake and a gun pipe breeching in such a way that the force transfer coupling between the breeching and the recoil brake is reduced with respect to the natural oscillations of the gun pipe, when firing a shot; the oscillation damper according to the invention being characterized in that the dimenions of the oscillation damper are such that the damper along with the recoil brake form a damping device having a rigidity substantially less than the recoil brake alone and constituting an oscillatory system with a natural frequency substantially lower than that of said natural oscillations of the gun pipe, when firing a shot. Advantageously, the elastic oscillation damper consists of a plurality of Belleville springs, preferably of the same shape, and being assembled in such a number to form a spring column that at maximum deflection, the springs in all are capable of elastically absorbing the maximum recoil force to which the recoil brake may be exposed, without the internal shearing forces in each individual spring exceeding the limit of elasticity. The invention also conserns a damping device for a gun pipe having a muzzle brake; said device comprising a recoil brake, preferably in the form of a viscous damper, and an oscillation damper to prevent natural oscillations in the gun pipe when firing a shot, from propagation to the recoil brake; the oscillation damper being coupled to the recoil brake and a gun pipe breeching in such a way that the force transfer coupling between the breeching and the recoil brake is reduced with respect to said natural oscillations. According to the invention the damping device is characterized in that the dimensions of the oscillation damper, preferably being designed as a column of Belleville springs, are such that the damping device as a whole has a rigidity substantially less than the recoil brake alone and forms an oscillatory system with a natural frequency substantially lower than that of the natural oscillations of gun pipe, when firing a shot. The substantially reduced rigidity of the damping device now causes parts of the recoil forces which previously were transferred- to the recoil brake, to be absorbed as inertial forces in the gun pipe and components connected thereto, at the same time as the fast oscillations of the gun pipe to a far lesser extent are transferred to the recoil brake due to the lower natural frequency of the system. In a preferred embodiment of the damping device according to the invention, the connection of the elastic oscillation damper to the recoil brake and the gun pipe breeching is designed so that the oscillation damper is exposed mainly to compression, when firing a shot. A particularly preferred embodiment of the damping device according to the invention, which is provided with a connection member for forced transfer from the gun pipe to a rod extending from one side of the connecting member to the recoil brake, when firing a shot, is characterized in that the elastic oscillation damper is mounted onto a portion of the rod to the recoil brake, which is on the other side of said connecting member; the recoil brake rod being movable in relation to the connecting member, preferably by loose guidance through the connecting member. Brief Description of Drawings Further features of present invention will appear from the following description of an example of a preferred embodiment by reference to the appended drawings, on which: Figure 1 illustrates a gun pipe having a prior art recoil brake, Figure 2 shows a typical sequence of discharge force transfer from the gun pipe to the recoil brake in the embodiment of Figure 1, Figure 3 is a cross sectional and a perspective view, respectively, of a Belleville spring in an oscillation damper according to present invention, Figure 4 is an enlarged sectional view of Figure 1 showing the oscillation damper installed according to the inventio , and Figure 5 shows a sequence of the discharged force transfer from the gun pipe to the recoil brake with an oscillation damper installed as demonstrated in Figure 4. Description of Preferred Ernbodiments Reference is first made to Figure 1 which shows a schematic outline of a gun pipe 1 provided with a muzzle brake 2 and a damping device constituted by a prior art recoil brake 3. The recoil brake 3 consists of a sylindrical hydraulic damper with piston and piston rod 6. A connecting member designed as an ear 4 is fixed to the cannon pipe breeching 5 for connection thereof to the rod 6 from the recoil brake, so that the recoiling parts of the gun is retarded by the recoil brake when firing the gun, the recoil brake rod 6 being permanently attached to the ear 4 by means of a lock nut 7. Figure 2 shows a typical oscillation sequence of the force which, when firing a shot, is transferred from the gun pipe 1 to the recoil brake 3 in an arrangement such as that shown in Figure 1. In Figure 2, the horisontal axis is the time axis, while the vertical axis indicates the forces in kN. The sequence shown relates to a test carried out by discharging a given type of shell with a specific propellant charge and gun pipe elevation, and indicates the measured momentary value of the force supplied to the recoil brake, from the instant when the gun is fired (t = 0) , till 175 s has elapsed. After the firing instant, the curve in Figure 2 rises to an average value of approx. 300 kN, which corresponds to the recoil force of the shell discharge itself. However, when the projectile has left the muzzle completely, an oscillating force with large amplitude is added to this average force, which causes the forces supplied to the recoil brake to vary between 0 and 650 kN, i.e. approx. ± 100 % about said average value. This oscillating force has a frequency which substantially corresponds to the longitudinal natural oscillations of the gun pipe, and is caused by the fact that the gas pressure against the muzzle brake stretches the pipe and brings it to oscillate. Recoil brakes in known damping devices of the kind shown in Figure 1, are in principle viscous dampers which serves to transform kinetic energy to thermal energy. By coupling an elastic oscillation damper, e.g. a spring, along with such a viscous damper, a visco-elaεtic damping device is achieved which according to the invention, is designed to attenuate the oscillating forces caused by the natural oscillation of the gun pipe. To achieve effective damping of oscillations, first of all the natural frequency of the oscillatory system constituted by the gun recoil brake and the oscillation damper, must be adjusted to lie within a desired range on the frequency axis, so that oscillations with frequency above a certain value are strongly attenuated. This is achieved by means of an elastic oscillation damper with the right rigidity in relation to the co-oscillating mass of the damping device. A further damping effect is achieved by the fact that a less rigid damping device (including recoil brake and elastic oscillation damper) will allow a larger portion of the forces which originally were transferred from the gun pipe to the recoil brake, to be absorbed as inertial forces in gun pipe and ear. This means that there are less recoil forces transferred to the recoil rod when the elastic oscillation damper is installed. This damping effect is an addition to the phase attenuation described above. Measurements have shown that the longitudinal natural frequency of a gun pipe with a total length of 6.5 m, including muzzle brake and breeching, is approx. 400 Hz. Hence, for the achievement of oscillation damping the natural frequency of the oscillating system which is consituted by the damping device, must be substantially lower. The natural frequency of this system is a function of the total rigidity incorporated in the oscillating system, including the co-oscillating mass. Both these quantities are difficult to determine, since both rigidity and mass are unevenly distributed across the system. However, to a certain degree the natural frequency may be estimated from a simplified calculation model. On this basis, the oscillation damper is dimensioned and tested so as to achieve a natural frequency which is well below the frequency of the gun pipe oscillations, which to the largest degree possible are to be prevented from transfer to the recoil brake. The only kind of springs means which in the present case is suitable for use in the elastic oscillation damper, and which is capable of absorbing the forces in question with little deformation, and having restricted external geometric dimensions, is Belleville or cup springs. Figure 3 shows a cross section through a Belleville spring of an oscillation damper for the present object, and Figure 4 shows a series of such Belleville springs 10 assembled to form the desired oscillation damper. In the shown embodiment according to the invention, the large and small diameters a, b of the Belleville spring are determined by the space available on the location where it is to be mounted, i.e. on an extension 8 of the recoil brake rod 6. It is also possible to prepare an adapter for the installation of the springs therein, thereby avoiding the need for extended the recoil brake rod itself to obtain enough space for the column of springs. Due to internal shearing forces in the Belleville springs when deflected, a plurality of thin springs must be used in stead of a few thick ones. The springs are arranged in a spring column 9 so that the total spring constant equals the sum of the individual spring constants. However, from the table below, which for the present type of Belleville spring shows the relationship between the deflection of an individual spring and its spring force, it appears that the spring force of a spring is not a linear function of the deflection across the entire deflection range of the spring. The largest force is absorbed at a deflection of approx. 3 mm. Deflection (mm) Spring force (N) As demonstrated in Figure 2, the momentary value of the recoil force varies between 0 and approx. 650 kN. Therefore, there will be no stretch in the springs of the oscillation damper and hence, it is sufficient to arrange springs only on one side of the ear 4, thereby exposing the springs to compression only, when firing a shot. Judged by the simple calculation model mentioned above, a number of 50 - 60 springs mounted on the extension 8 of the recoil brake rod will give the oscillating system a natural frequency of 125 - 150 Hz, which is well below 400 Hz, i.e. the frequency of the force oscillations exerted on the recoil brake rod. Figure 5 shows the sequence of the recoil force which, when firing, is transferred from the gun pipe 1 to the recoil brake 3 in the damping device having an oscillation damper 9 mounted according to Figure 4. As in Figure 2, the vertical axis indicates the forces in kN and the horisontal axis the time in ms. The lauching is carried out with the same given type of shell, and the same propellant charge and gun pipe elevation as in the case demonstrated in Figure 2. By comparing Figures 2 and 5, it clearly appears that a substantial improvement is achieved. The maximum force is reduced to less than the half the value, and the oscillations are as good as eliminated. In other words, the sequence of force transfer from gun pipe to recoil brake is changed substantially in favourable direction. A note is made to the fact that the longitudinal natural oscillations of the gun pipe are unchanged. The task of the oscillation damper is merely to prevent the force oscillations from reaching the recoil brake of the damping device.

Claims: Claims 1. An elastic oscillation damper to prevent natural oscillations which, when firing a shot, arise in a gun pipe having a muzzle brake, from propagation to a recoil brake for the gun pipe; said oscillation damper being designed to be connected to the recoil brake and a gun pipe breeching in such a way that the force transfer coupling between the breeching and the recoil brake is reduced with respect to said natural oscillations, c h a r a c t e r i z e d i n that said oscillation damper (9) is dimensioned so that the damper along with the recoil brake (3) form a damping device having a rigidity substantially less than the recoil brake alone and consti¬ tuting an oscillatory system with a natural frequency substantially lower than the frequency of said natural oscillations of the gun pipe, when firing a shot. 2. An oscillation damper accordning to claim 1, c h a r a c t e r i z e d i n that the oscillation damper (9) comprises a plurality of Belleville springs (10) , preferably of the same shape; said Belleville springs being assembled to form a spring column. 3. An oscillation damper accordning to claim 2, c h a r a c t e r i z e d i n that said Belleville springs (10) are assembled in such a number that at maximum deflection, the springs. in all are capable of elastically absorbing the maximum recoil force to which the recoil brake (3) may be exposed, without the internal shearing forces in each individual spring exceeding the limit of elasticity. 4. An oscillation damper accordning to claim 2, c h a r a c t e r i z e d i n that the Belleville springs (10) are dimensioned to get a maximum deflection when firing a shot, which approximately corresponds to the deflection at which an individual spring has its maximum spring force. 5. A damping device for a gun pipe (1) having a muzzle brake (2) ? said device comprising a recoil brake (3) , preferably in the form of a viscous damper, and an oscillation damper to prevent natural oscillations in the gun pipe when firing a shot, from propagation to the recoil brake; the oscillation damper being coupled to the recoil brake and a gun pipe breeching (5) in such a way that the force transfer coupling between the breeching and the recoil brake is reduced with respect to said natural oscillations, c h a r a c t e r i z e d i n that said oscillation damper (9) , preferably being designed as a column of Belleville springs (10) , is dimensioned so that the damping device as a whole has a rigidity substantially less than the recoil brake alone and forms an oscillatory system with a natural frequency substantially lower than the frequency of said natural oscillations of the gun pipe, when firing a shot. 6. A damping device according to claim 5, c h a r a c t e r i z e d i n that the connection of said elastic oscillation damper (9) to the recoil brake (3) and the gun pipe breeching (5) is designed so that the oscilla¬ tion damper is exposed mainly to compression, when firing a shot. 7. A damping device according to claim 5 or 6, and provided with a connecting member (4) for force transfer from the gun pipe to a rod (6) extending from one side of the connecting member to the recoil brake (3) , when firing a shot, c h a r a c t e r i z e d i n that said elastic oscillation damper (9) is mounted onto a portion (8) of the rod (6) to the recoil brake, which is on the other side of said connecting member (4) ; the recoil brake rod (6) being movable in relation to the connecting member, preferably by loose guidance through said connecting member.

Inventors: ARNESEN GERT, BERGERSEN BJOERN, ARNESEN, GERT, BERGERSEN, BJOERN
Applicants: FORSVARETS FORSKNINGS, FORSVARETS FORSKNINGSINSTITUTT
Application year: 1992
Main classification: F41A25
IPC codes: F41A21, F41A25