Multiple pulse cartridge ignition system

The U.S. Government has interests in this invention pursuant to Contract #DAAA21-87-C-0160 awatded by the Department of the Army

Field of the Invention

The present invention is in the field of cartridge ignition systems and, more particularly, relates to an electronically controlled dual event or multi-pulse ignitor which can sense the temperature of the cartridge and adjust the ignition for a cartridge.

Background of the Invention

One of the most important design variables in ammunition development is the performance of a cartridge over the operating temperature range. This performance is currently limited by the operating pressure at hot temperatures.

Attempts to improve cartridge performance over a range of temperatures have typically relied on mechanical devices and propellant innovations. Propellant design, for example, has long focused on chemically creating a propellant to reduce performance differences over temperature. A mechanical design which has been explored uses control tube concepts to modify the initial travel of the projectile as a function of temperature using material thermal expansion or bimetallic strips.

United States Patent 4,930,421, issued June 5, 1990, to Macdonald, entitled "Partitioned, Fluid Supported, High Efficiency Traveling Charge for Hyper-velocity Guns," discloses a traveling charge projectile that utilizes a microprocessor and a plurality of sequentially fired igniting-priming-expelling charges to initiate respective charge segments containing propellant.

The ignitor can be reprogrammed externally.

In contrast, the instant invention provides an ignition system known as a Smart Cartridge Ignition System, described hereinbelow, that controls the performance of a cartridge so that it is substantially invariant over ambient and cold temperature ranges

Summary of the Invention

According to the present invention, an electronically controlled multi-pulse ignitor for a cartridge as defined in independent claim 1 and a method for igniting a cartrige as defined in independent method claim 10 are provided for launching a projectile.

Advantageous embodiments are claimed in dependent claims 2 to 9 and 11 to 14.

Brief Description of the Drawings

• Figure 1A schematically shows a block diagram for one example of an electronically controlled multi-pulse ignitor system constructed in accordance with the present invention.
• Figure 1B illustrates a process flow diagram for one example of an electronically controlled multi-pulse ignitor system algorithm constructed in accordance with the present invention.
• Figure 2 and Figure 2A show a partially cut-away view of one example of a cartridge including an electronically controlled multi-pulse ignitor system constructed in accordance with the present invention.
• Figure 3 schematically shows a view of an example of a cartridge system constructed in accordance with the present invention in an initial cartridge configuration.
• Figure 4 schematically shows an example of a cartridge system constructed in accordance with the present invention in a translational cartridge configuration.
• Figure 5 schematically shows a view of one example of a cartridge system constructed in accordance with the present invention in a cartridge configuration after main charge ignition.
• Figure 6 graphically shows a comparison of one example of performance of a cartridge system constructed in accordance with the present invention against a conventionally ignited cartridge

Detailed Description of the Preferred Embodiment

Referring now to Figure 1A, a block diagram for one example of an electronically controlled multi-pulse ignitor system constructed in accordance with the present invention is shown. The system comprises a temperature sensor 16, a pressure sensor 105, a movement sensor 80, an electronics module 9, a first initiator 61 and a second initiator 70. Depending upon the cartridge system being ignited, a firing pulse will be generated either by an electronic firing pulse 5 in the case of an electronically fired cartridge, or a percussive firing pulse 6, in the case of a percussion fired cartridge. Electronics module 9 comprises a temperature profile memory 11 and an algorithm 10. Electronics module 9 includes electronics suitable for processing data and executing algorithm 10. It is contemplated herein that the novel process be constructed, and has been so constructed by the inventors, using standard electronics. Other useful embodiments may be constructed using digital circuitry and/or programmable computer, application specific integrated circuits, or microprocessor devices, components or equivalents using well known design principles.

Temperature profile memory 11 stores a temperature and event delay performance profile for a given cartridge. The temperature profile may be empirically derived from temperature and performance data for a cartridge using standard profiling techniques. The electronics module controls the first initiator 61 and the second initiator 70 by processing temperature data from the temperature sensor 16, pressure sensor 105 and movement sensor 80 with the temperature profile information as discussed in detail below with reference to the figures.

Referring now to Figure 1B, a process flow diagram for an electronically controlled multi-pulse ignitor system constructed in accordance with the present invention is shown. The process flow diagram shows one example of an algorithm 10. The algorithm 10 is initiated by the receipt of a firing pulse at event 12. The firing pulse is transmitted to a second event, fire primer event 14, where the first initiator is fired. The fire primer event 14 provides a signal to a decision event 18 for determining an appropriate delay. The decision event 18 receives current temperature data from temperature sensor 16 within the cartridge system. Decision event 18 determines an appropriate delay by comparing the current temperature data with the stored cartridge temperature profile information, and it sends a count down period to event timer 20. Event timer 20 counts down amount of time determined at event 18 before finng the second ignitor.

During the countdown period, a second decision event 26 decides whether or not it is safe to fire the second ignitor. The safe determination is made using a first safety signal 22 from either the pressure sensor 105 and/or a second movement safety signal 24 from the movement sensor 80. If the pressure sensor 105 is activated, the first safety signal 22 is positive, allowing firing. Similarly, if movement is detected from the movement sensor 80, the second safety signal 24 is positive for allowing firing. In one embodiment, if either the pressure sensor activated event 22 or the movement sensor activated event 24 is negative, the safe to fire decision 26 transmits an abort signal to abort firing at event 28. If both the pressure sensor activated event 22 and the movement sensor activated event 24 are positive, the safe to fire decision 26 transmits a firing signal to fire the second ignitor at event 30.

Referring now to Figure 2 and Figure 2A, a partially cut-away view of one example of a cartridge including an electronically controlled multi-pulse ignitor system constructed in accordance with the present invention is shown. It will be understood that the configuration shown herein is by way of example and that the invention is not so limited. A projectile 50 includes a cartridge 58 wherein an ignition system 60 is located.

Referring now particularly to Figure 2A, an expanded, more detailed, schematic view of the cartridge 58 and ignition system 60 is shown. The ignition system 60 includes a first initiator 61, an electronics module 9, the second initiator 70 and a main charge ignition 67. The first initiator 61 includes an ignitor tube translation system 64, a firing contact 62, and a first initiator charge 90 The ignitor tube translation system 64 includes an exterior tube 402 at least partially movably sheathed around an interior tube 404. Attached to the electronics module 9 is a safety sensor 80 and a pressure sensor 105. The main charge ignition 67 further includes a second initiator 70 and a candelabra ignitor 102. The safety sensor 80 is coupled to the electronics module 9 by wire 97. The pressure sensor 105 is coupled to the electronics module 9. Similarly, the second initiator 70 is coupled to the electronics module by conductor 92.

The electronics module 9 may advantageously comprise analog and/or digital electronics, or both for implementing algorithm 10. Alternatively, the electronics module may include a CPU processor programmed to carry out the steps of algorithm 10. A memory or look up table may be used to store the temperature profile of a selected cartridge. Those skilled in the art, having the benefit of this disclosure, will understand that several equivalent embodiments of the invention are contemplated herein. For example, in the case of an electrically fired cartridge, like the 120mm M256 Tank Cannon, the electronics module can be completely powered from the firing pulse. In contrast, for a percussion fired cartridge, the power for the electronics can be contained in the cartridge but can be isolated by a mechanical switch which can be thrown when the firing pin strikes the primer.

The delay between the first and second initiator firings is a function of temperature. Longer delays allow more forward movement of the projectile, thereby increasing free volume. The delay is typically longer at higher temperatures than at lower temperatures, so that more free volume is available to keep the pressure low. It follows that the delay is shorter at lower temperatures, so that there is less volume, increasing the performance. Temperature profiles for different cartridge types will vary and event timing will vary accordingly. Useful second event timing may advantageously be derived empirically from data such as is shown below with reference to Figure 6. For example, about a 5 millisecond delay between firing of the first and second events has been shown to improve performance of the standard shell measured tested in the temperature ranges shown in Figure 6. Those skilled in the art and having the benefit of this disclosure will understand that other cartridge types may require different, and widely varying, timing delays.

The ignitor tube translation system 64 of the example embodiment includes two interlocking tubes 402, 404 which contain a small propellant charge 90. The translation mechanism is dependent upon the geometry of the projectile and cartridge in which a dual event ignition system is integrated. The first initiator 61 ignites the small propellant charge 90, moving the projectile forward. Any other system which moves the projectile forward without igniting the main charge can be used.

Since a dual event ignition system constructed for a particular cartridge will use the same propellant charge over all temperatures, the safety sensor 80 may advantageously be integrated into the system to ensure that the first ignitor functions properly before the second ignitor is initiated. In one embodiment, a ring movement sensor coupled to the translator tubes opens a circuit in the electronics module after the projectile translates forward and separates the interlocking tubes. The open circuit serves as a signal to subsequently arm the second ignitor. A second embodiment consists of a simple plug which is shorted when attached to the rear of the projectile and is pulled from the projectile by the translation event, thereby opening the circuit.

Referring now to Figure 3, a schematic view of an example of a cartridge system constructed in accordance with the present invention in an initial cartridge configuration is shown. A projectile 50, with a cartridge having an electronic multi-pulse ignition system 60 is placed within a gun tube 40 prior to ignition of the first ignitor.

Referring now to Figure 4, an example of a cartridge system constructed in accordance with the present invention in a translational cartridge configuration is shown schematically. Figure 4 shows events after firing of the first ignitor charge 90. It can be seen that the projectile 50 is moving forward with respect to the initial position. In operation, as exterior tube 402 moves forward it separates from interior tube 404. Safety sensor 80, being also mechanically coupled to the ignitor tube translation system 64, then operates to send a movement sensor activation signal to the electronics module 9 to indicate whether or not it is safe to fire the second ignitor 70, as explained above with respect to the process flow diagram of Figure 1. At the same time, the pressure from firing the first ignitor charge 90 activates a signal in an optional pressure sensor 105 indicating that it is safe to trigger the second initiator 70 for firing the main charge ignition system 67.

Referring now to Figure 5, a schematic view of one example of a cartridge system constructed in accordance with the present invention in a cartridge configuration after main charge ignition is shown. As shown in Figure 5, the cartridge is launched by firing of the main charge ignition system as indicated generally by flame indicators shown as shading 500. In accordance with this example of the invention, the main charge ignition system is not lit until after a count down period after firing of the first initiator.

Referring now to Figure 6, a graphical comparison of one example of performance of a cartridge system constructed in accordance with the present invention against a conventionally ignited cartridge is shown. The Figure 6 graph includes a first vertical axis 610, second vertical axis 612 and a horizontal axis 614. Also shown are a first curve plotted curve 602 and second plotted curve 604. The first vertical axis 610 indicates muzzle velocity in meters per second for a first cartridge, namely, model TERM-KE. The second vertical axis 612 indicates muzzle velocity in meters per second for a second cartridge, namely, model M829A2.

The TERM-KE cartridge, plotted on curve 602, incorporates the electronic multi-pulse ignition system of the invention, and the M829A2 cartridge, plotted on curve 604, is a conventional ignition system typical of high performance 120mm tank ammunition. Horizontal axis 614 indicates test temperatures in degrees Fahrenheit. Note that test data for temperatures between -25 degrees F and + 120 degrees F shows the TERM-KE cartridge maintained essentially the same muzzle velocity while the conventional M829A2 cartridge showed a drop of over 10% in muzzle velocity as the temperature diminishes.