The present invention relates to a shell to be fired from a barrel, where the shell constitutes a shell body comprising at least two warheads axially arranged one after another in the shell body, which at least two warheads comprises explosive charges arranged for shaped charge fragmentation effect in the direction of travel of the shell. The present invention also applies to a procedure for firing said shell.

Conventional mortar shells are normally of the type circumferential, lateral airburst, which entails that fragmentation that forms when the shell detonates, is radially dispersed outwards from the entire shell body. Fragmentation of the shell body is "natural", which means that the shell body, which normally is normally composed of iron or steel, is burst into fragments of varying forms and sizes. During combat in built-up areas, it is desirable to avoid damages to the civilian population. Shells with circumferential, lateral airburst fragmentation effect make it difficult to limit effect only towards military targets. The risk is great that fragments will be dispersed in directions resulting in undesirable effect. Fragments from naturally fragmented shell bodies are irregular in form and vary from very small to large fragments of the shell body. Furthermore, naturally fragmented, irregularly shaped fragments entail substantial air braking of the fragmentation and little effect on target, especially when the shells burst a great distance from the target.

It has been previously known to reduce the circumferential, lateral fragmentation effect of a shell by using explosive charges with shaped charge effect. To increase the fragmentation effect of the shell it is also known to use several shaped charges sequentially after each other in a series, where each shaped charge initiates with a specific time delay. US 5 191 169 Figure 1 depicts such a shell (1) where a number of shaped charge modules (16), also known as Explosively Formed Penetrator (EFP) modules, are arranged one after another. Shaped charge modules (16) comprising seven shaped charges (22) each, of which one shaped charge is arranged in the centre of the shaped charge module while the others are evenly distributed around the central shaped charge (22). Shaped charge (22) comprises; one shaped charge liner (24), one explosive charge (26), and one detonator (28). The intended direction of warhead effect for the central shaped charge is directed in the direction of travel of the shell. The circumferential, lateral airburst shaped charge is however angled, radially outwards in relation to the central shaped charge and thereby prevents disrupting a shaped charge module in front of it. The arrangement in US 5 191 169, where the shaped charge behind is radially angled or deflected, does not however solve the problem of the dispersion of fragments from the surrounding shell body .

An additional disadvantage of the arrangement in US 5 191 169 is that the dispersion of fragments from the shaped charge increases with the number of shaped charge modules in the shell.

Inventions objective and its distinctive features

One main objective of the present invention is a shell comprising warheads arranged for shaped charges in the direction of travel of the shell with greatly reduced radial dispersion of fragments and where fragmentation effect on a well-defined has increased. An additional objective of the present invention is a procedure for firing a shell as described above. The objectives so named, as well as other purposes, not mentioned here, are satisfactorily achieved within the framework specified in the present independent patent claims.

Thus, in accordance with the present invention, a shell has been accomplished constituting a shell body comprising a minimum of two warheads axially arranged one after the other in the shell casing, where the warheads comprise explosive charges arranged for shaped charge fragmentation effect in the shell's direction of travel, where dispersion of fragments is radially greatly reduced and where fragmentation effect to a well-defined area has been increased. Characteristic for the present invention is that the shell body also comprises the ejecting device for ejecting the warheads from the shell body in accordance in a determined time sequence in the direction of travel of the shell, and initiating device for initiating the explosive charges of the warheads in accordance with determined time sequence.

The following additional aspects for a shell, as claimed in the present invention, apply: that the ejecting devices and initiation devices are arranged in the warheads, that the warheads also comprise a programmable time delay unit for time delayed ejection and initiation of the warheads, that the shell also comprises a sensor unit arranged in the nose section for activating the ejecting devices of the warheads that the rears of the warheads comprise an endpiece, said endpiece being shaped so that a warheads following behind at any rate can partly be contained in a warhead in front, that the warheads comprise a fragmentation plate, said fragmentation plate comprising pre-fragmented metallic fragmentation baked into a powder metallurgic material, that the pre-fragmented metallic fragments comprise a heavy metal or a mixture of heavy metals, that the warhead comprises a casing; said casing comprising a plastic matrix made of a metallic powder.

Characteristic for the procedure during firing of the shell as described above are the following; that the warheads of the shell are ejected from the shell body in the direction of travel of the shell with the same time delay in relation to each other and that the warhead explosive charges detonate simultaneously after a determined time delay.

Advantages and effects of the invention

The present invention involves several advantages and effects. Separating the warheads from the shell before initiating the explosive charges of the warheads, fragmentation from the shell body is prevented from dispersing radially. Separating the warheads from one another before initiating the explosive charges of the warheads minimizes the disruptive effect of the warhead behind on the warhead in front of it. Reduced dispersion means that shaped charge effect on a well- defined area increases. Using several fragmentation plates compared with using one or a couple of fragmentation plates results in the increase in the amount of fragmentation the shell can accomplish. Further the use of pre-fragmented heavy metal fragmentation provides a lower dispersion effect since pre-fragmented heavy metal fragments are more uniform in shape with a higher density. The air braking effect of fragmentation in the atmosphere is reduced while penetration force increases compared with naturally fragmented steel fragmentation.

Varying the dispersal frequency and bursting frequency of the warheads enables the variation of fragmentation dispersal and fragmentation effect to conform to the position and character of the target. Additional advantages and effects as claimed in the present invention will be presented in the study and in observation of the following detailed description of the invention, including a number of the most advantageous forms of execution, patent claims, and the appended drawing figurers where:

Figure 1 depicts a longitudinal section of a shell comprising four warheads arranged for shaped charge effect,

Figure 2, depicts a longitudinal section of a warhead as shown in Figure 1,

Figure 3 diagrammatically depicts the dispersion of fragments A from the warheads with burst interval H.

Detailed description of embodiments

Figure 1 depicts a preferred embodiment of the shell 1 as claimed in the present invention. The shell 1 is shaped like a conventional mortar shell 1 but could be another type of shell 1, for example an artillery shell 1. Shell 1 comprises a shell body 2, a nose section 3, and a rear section 4. The shell body 2 comprises four warheads radially arranged one after the other 8, formed for shaped charge effect. The shell 1 is arranged for shaped charge effect with well-defined effect on target from the warheads 8. The rear section 4 in Figure 1 comprises a forward tubular section 7 designed for assembling conventional horseshoe-shaped propellant charges for firing the shell 1 out of a barrel. The rear part of the rear section 4 is arranged with a number of fins 6 for guidance of the shell 1 during the flying phase of the shell 1.

The shell 1 in Figure 3 is primarily intended to air burst over a target located in an urban environment where the objective is to put effect on target while avoiding unwanted side effects on the civilian population and civilian equipment.

The purpose is therefore that fragments from the shell 1 and its warheads 8 shall be ejected in the direction of travel of the shell 1 forward direction and that no, or if possible fragmentation with a very limited range shall be radially dispersed. The coverage area (A) on target of the shell 1 can be adjusted, for an air burst, to the position and character of the target by selecting a suitable height of burst (H) . A low height of burst (H) results in a small coverage area (A) and a high height of burst (H) results in a large small coverage area (A) . To attain this effect, the shell 1 is equipped with a sensor unit 5, said sensor unit 5 can be comprised of a time delay or proximity fuse 5, which can be programmed for the suitable height of burst (H) , Figures 1 and 3. The warheads 8 of the shell 1, Figure 2, comprise a fragmentation plate 10 and a warhead casing 11 also designated the casing 11. Every warhead 8 comprises an explosives charge 12 and a programmable detonation device 13, also designated the Safety, Arming, and Ignition (SAI) unit 13, said detonation device 13 comprises a gas generator 15 for ejecting the warheads 8 from the shell body 2 and a detonator 14 for detonation of the explosive charge 12 of the warheads 8. The detonation device 13 further comprises one time delay unit (not depicted in Figure 2) for time delayed ejection and initiation of the warheads 8.

The rear section of the warheads 8 preferably comprise a tubular endpiece 16 for facilitating fitting the warhead 8 behind, at least partially, in a warhead 8 in front of it, that is, the warheads are thereby 8 stackable in each other, whereby valuable space can be saved in the shell 1. The tubular shape of the endpieces (16) also has a stabilising effect when ejecting the warheads 8 from the shell body 2. The fragmentation plate 10 in Figure 2 comprises pre fragmented metal fragments, preferably comprising one heavy metal or a mixture of heavy metals, for example tungsten. The metal fragments are preferably baked into a matrix material, with the purpose of holding the pre-fragmented heavy metal fragments together and functions as the pusher plate when the explosive charge 12 detonates. The matrix material can, for example, be composed of a powder metallic material formed to its final shape through, for example, isostatic pressing. The fragmentation plate 10 is shaped, together with the detonating explosive charge 12, to generate an even dispersal of fragments over the target area (A) . Warheads 8 are comprised of a casing 11 that is arranged to provide a suitable confinement (charge) for detonation of the explosive charge 12. The casing 11 preferably comprises a material that provides very little fragmentation effect upon detonation of the explosive charge 12. Fragments that do form will have a very short range. Explosive charge 12 is preferably comprised of a low sensitivity explosive, for example of type nitramine. The detonation device 13 for the warheads 8, which can be an SAI device 13, handles the functions for: safety, arming and initiation of the warheads 8. The SAI unit 13 also controls the gas generator 15 for separation of the warheads 8.

The shell 1 is fired from the barrel, for example a mortar barrel, like conventional shell 1. When the shell 1 gets close to the target the time delayed fuse 5 activates and the shell 1 effect phase initiates.

Nose section 3 of the shell 1 is ejected by a separation charge (not depicted in Figure 1); said separation charge is arranged in the rear section of the fuse 5, alternatively, an airbag may be used as a separation charge.

Prior to ejection from the shell body 2, the time delayed fuse 5 activates the SAI unit 13 in the warheads 8. After the nose section 3 with the time delayed fuse 5 has been ejected from the shell body 2, the ejection sequence for the warheads 8 starts. The gas generators 15 in the warheads 8 then handle ejection of the warheads 8 from the shell body 2, which entails separating the warheads 8 from each other .

The warheads 8 are ejected from the shell body 2 starting with the warhead 8 farthest to the front, closest to the nose section 3 of the shell 1, followed by the remaining warheads 8 in rapid succession. At the same time as the warheads 8 leave the shell body 2, the SAI unit 13 arms the explosive charges 12 in the warheads 8.

When all of the warheads 8 have left the shell body 2, the SAI unit 13 detonates the explosive charges 12 through the detonators 14 at which time the warheads 8 detonate and fragments are dispersed forward in the direction of travel of the shell 1. The time delay unit in the SAI unit 13 initiates the warheads 8 so that all of the warheads 8 detonate, preferably simultaneously. Alternatively, he time delay unit can be pre-programmed so that the warheads 8 detonate with different time delays. For example, the time delay can be such that all warheads 8 detonate at the same range from a target. It is also possible to have different time delays for ejection of the warheads 8 and different time delays for initiation of the explosive charges 12 of the warheads 8.

The purpose of time-delayed ejection is to achieve a pre-determined distance between the warheads 8 so that the warheads 8 do not disrupt each other when they detonate. The distance between the warheads should, preferably, be the smallest possible but still large enough so that the warheads 8 do not disrupt each other. The time of flight for the warheads 8, after ejection from the shell body 2, should be as short as possible so that the warheads 8 do not have time to change course. The result is that all fragmentation plates 10 in the warheads 8 simultaneously disperse their fragments at a well-defined target area (A) .

The shape of the fragmentation plates 10 can also be adapted to achieve a pre-determined dispersion pattern of fragments on target. Additionally, area dispersion (A) on target can be varied by varying burst interval (H) .

Possible alternative uses for the shell

When using the shell 1 as a conventional mortar shell 1, the entire shell 1 can be detonated without ejecting the warheads 8 from the shell body 2. All of the warheads 8 detonate simultaneously in the shell body 2, which means that all of the explosive charges 12 initiate simultaneously. The shell 1 then has a circumferential, lateral fragmentation effect, partly from the fragmentation plate 10 that to some extent disperses radially, and partly from fragments of the shell body 2 that are dispersed radially.

Another possibility is to separate the warheads 8 at high altitude over the target and allow them to travel individually for a period of time to disperse the warheads 8 over a large target area (A) . However, this option means the loss of exact control over where each warhead 8 applies its effect.

Figure 3 depicts a shell 1 that is enroute to a target in a trajectory with a steep angle of impact, which is the traditional method for deploying a mortar for indirect fire with a high trajectory. However, there is nothing to prevent using the shell 1 for direct fire with a flat trajectory.