Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
  • B60R21/00—Arrangements or fittings on vehicles for protecting or preventing injuries to occupants or pedestrians in case of accidents or other traffic risks
  • B60R21/02—Occupant safety arrangements or fittings, e.g. crash pads
  • B60R21/16—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags
  • B60R21/26—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow
  • B60R21/263—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow using a variable source, e.g. plural stage or controlled output
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
  • B60R21/00—Arrangements or fittings on vehicles for protecting or preventing injuries to occupants or pedestrians in case of accidents or other traffic risks
  • B60R21/02—Occupant safety arrangements or fittings, e.g. crash pads
  • B60R21/16—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags
  • B60R21/20—Arrangements for storing inflatable members in their non-use or deflated condition; Arrangement or mounting of air bag modules or components
  • B60R21/217—Inflation fluid source retainers, e.g. reaction canisters; Connection of bags, covers, diffusers or inflation fluid sources therewith or together
  • B60R21/2171—Inflation fluid source retainers, e.g. reaction canisters; Connection of bags, covers, diffusers or inflation fluid sources therewith or together specially adapted for elongated cylindrical or bottle-like inflators with a symmetry axis perpendicular to the main direction of bag deployment, e.g. extruded reaction canisters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
  • B60R21/00—Arrangements or fittings on vehicles for protecting or preventing injuries to occupants or pedestrians in case of accidents or other traffic risks
  • B60R21/02—Occupant safety arrangements or fittings, e.g. crash pads
  • B60R21/16—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags
  • B60R21/26—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow
  • B60R21/264—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow using instantaneous generation of gas, e.g. pyrotechnic
  • B60R21/2644—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow using instantaneous generation of gas, e.g. pyrotechnic using only solid reacting substances, e.g. pellets, powder
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06D—MEANS FOR GENERATING SMOKE OR MIST; GAS-ATTACK COMPOSITIONS; GENERATION OF GAS FOR BLASTING OR PROPULSION (CHEMICAL PART)
  • C06D5/00—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets
  • C06D5/06—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets by reaction of two or more solids
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F42—AMMUNITION; BLASTING
  • F42B—EXPLOSIVE CHARGES, e.g. FOR BLASTING, FIREWORKS, AMMUNITION
  • F42B10/00—Means for influencing, e.g. improving, the aerodynamic properties of projectiles or missiles; Arrangements on projectiles or missiles for stabilising, steering, range-reducing, range-increasing or fall-retarding
  • F42B10/32—Range-reducing or range-increasing arrangements; Fall-retarding means
  • F42B10/48—Range-reducing, destabilising or braking arrangements, e.g. impact-braking arrangements; Fall-retarding means, e.g. balloons, rockets for braking or fall-retarding
  • F42B10/56—Range-reducing, destabilising or braking arrangements, e.g. impact-braking arrangements; Fall-retarding means, e.g. balloons, rockets for braking or fall-retarding of parachute or paraglider type
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F42—AMMUNITION; BLASTING
  • F42B—EXPLOSIVE CHARGES, e.g. FOR BLASTING, FIREWORKS, AMMUNITION
  • F42B12/00—Projectiles, missiles or mines characterised by the warhead, the intended effect, or the material
  • F42B12/02—Projectiles, missiles or mines characterised by the warhead, the intended effect, or the material characterised by the warhead or the intended effect
  • F42B12/36—Projectiles, missiles or mines characterised by the warhead, the intended effect, or the material characterised by the warhead or the intended effect for dispensing materials; for producing chemical or physical reaction; for signalling ; for transmitting information
  • F42B12/56—Projectiles, missiles or mines characterised by the warhead, the intended effect, or the material characterised by the warhead or the intended effect for dispensing materials; for producing chemical or physical reaction; for signalling ; for transmitting information for dispensing discrete solid bodies
  • F42B12/58—Cluster or cargo ammunition, i.e. projectiles containing one or more submissiles
  • F42B12/60—Cluster or cargo ammunition, i.e. projectiles containing one or more submissiles the submissiles being ejected radially
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F42—AMMUNITION; BLASTING
  • F42B—EXPLOSIVE CHARGES, e.g. FOR BLASTING, FIREWORKS, AMMUNITION
  • F42B3/00—Blasting cartridges, i.e. case and explosive
  • F42B3/04—Blasting cartridges, i.e. case and explosive for producing gas under pressure
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
  • B60R21/00—Arrangements or fittings on vehicles for protecting or preventing injuries to occupants or pedestrians in case of accidents or other traffic risks
  • B60R21/02—Occupant safety arrangements or fittings, e.g. crash pads
  • B60R21/16—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags
  • B60R21/26—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow
  • B60R21/264—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow using instantaneous generation of gas, e.g. pyrotechnic
  • B60R21/2644—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow using instantaneous generation of gas, e.g. pyrotechnic using only solid reacting substances, e.g. pellets, powder
  • B60R2021/2648—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow using instantaneous generation of gas, e.g. pyrotechnic using only solid reacting substances, e.g. pellets, powder comprising a plurality of combustion chambers or sub-chambers

Definitions

• This invention relates to a dual or multi-stage gas generator that utilizes an improved gas generant formulation or formulations.
• Gas generators also known as inflators, have numerous commercial and military applications. For example, they may be used to deploy airbags used in automobiles, to inflate floatation devices, and may be used in oxygen generating devices. For further example, gas generators may be used to inflate airbags used in deploying and aiming submunitions.
• Gas generators operate by burning a propellant contained therein extremely rapidly, usually in the millisecond range. Until now, gas generators have typically burned the propellant in airbags in one stage, causing, providing less than optimal control over the deployment.
• the propellants used in airbags have generally contained sodium azide, which, upon ignition, yielded particulates, including hot metallic oxides, and corrosive products, thus requiring expensive filtering systems to be certain these products do not damage the munitions or related equipment.
• Alternative propellants have produced high temperature effluent and/or gases including various oxides of nitrogen (NO x ), which also have required systems to protect the equipment.
• Such airbag systems have also required various protective coatings, in order to prevent damage to the bags caused by the harmful by-products of combustion.
• these gas generant formulations Upon combustion, these gas generant formulations generate very hot copper-based, iron-based, or molybdenum-based solid byproducts, as well as NO, NO , SO 2 , CO, and CO 2 . Such byproducts many times can escape controls. Some of these combustion byproducts are extremely toxic to humans and may be of great concern even if such gas generant byproducts are produced in only small quantities.
• U.S. Patent No. 5,876,062 relies on using a resistance wire to ignite the propellant. Vibration of the airbag system can cause the ignition wire to break, leading to malfunction of the system. Furthermore, a filtration system is also required.
• U.S. Patent No. 6,199,906 relies on electronic logic to determine the extent to which the airbag is deployed. However, the system still generates noxious effluent and attempts to eliminate them through certain gas ports.
• the system recognizes that there may be accidental ignition of some portions of the system when exposed to heat or fire.
• This invention relates to a gas generator having two or more compartments, each with a separate initiator, with one compartment discharging before another, i.e., the compartments discharge sequentially.
• An objective of the present invention is to provide a gas generator with reduced weight, size and fewer geometric constraints from the design perspective. It is also an objective to eliminate the need for a filter system. It is also an objective to provide a gas-generating inflator, which eliminates or at least reduces the size of the internal structural members of the pressure vessel, i.e., combustion chamber. It is a further objective to provide a less costly gas generator, both in terms of fewer parts and lower process manufacturing operations.
• One embodiment may include a gas generator including at least two chambers. Each chamber may be capable of discharging gas at a different time and different volumetric rate and each chamber may contain an initiator and the same propellant that is in the other chamber(s).
• the gas generator may include a propellant that is composed of on a weight basis approximately (a) 84-95% of an oxidizer, (b) 3.4-13.4% of a fuel, and (c) 1.5-2.6% of a binder.
• the products of combustion of the propellant may be non-toxic gases.
• the propellant fuel may be selected from CL-20, RDX, HMX, GAP, NGU, TATB, LLM-105, EDNA, and mixtures thereof.
• the binder may be selected from PCL, PIB, GAP, polyvinylpyrrolidone, and mixtures thereof.
• the oxidizer may be ammonium nitrate.
• the propellant may include on a weight basis approximately 70-95% energetic nitramine fuel, 5- 25% energetic polymer binder and 0.1-5% flash suppressant.
• a second embodiment may include a process for controlling the rate of inflation of an airbag.
• a gas generator having at least two chambers that are each capable of discharging gas at a different rate may be connected to the airbag.
• Each of the chambers may be caused to discharge gas or effluent at a different, predetermined time.
• the process may include causing the effluent of each of said chambers to flow into the airbag.
• the gas generator may be positioned in a vehicle and may be activated in response a vehicle collision.
• the airbag may be used for ejecting one or more submunitions from a weapon and the gas generator may be activated in response to a trigger signal.
• the trajectory of a submunition may be controlled by deployment of the airbag.
• a third embodiment may include a process of using a multi-stage gas generator, having on a weight basis approximately 70-95% energetic nitramine fuel, 5-25% energetic polymer binder and 0.1-5% flash suppressant,for propelling small, medium and large caliber ammunition from a weapon system.
• the gas generator may be inserted into a barrel of a weapon system and ammunition may be inserted.
• the gas generator may be activated and gas expelled from the gas generator may be used to propel the ammunition.
• a fourth embodiment may include an eco-friendly gas generant propellant.
• the eco-friendly gas generant propellant may be composed of (a) 84-95% of an oxidizer on a weight basis, (b) 3.4-13.4% of a fuel on a weight basis, and (c) 1.5-2.6% of a binder, on a weight basis.
• the products of combustion of the propellant may be non-toxic gases.
• the eco-friendly gas generant propellant fuel may be selected from CL-20, RDX, HMX, GAP, NGU, TATB, LLM-105, EDNA, and mixtures thereof.
• the eco-friendly gas generant propellant binder may be selected from PCL, PIB, GAP, polyvinylpyrrolidone, and mixtures thereof.
• the eco-friendly gas generant propellant oxidizer may be ammonium nitrate.
• the same propellant may be used in each compartment or chamber.
• the propellants may have different geometries in each compartment, which results in different rates of gas evolution from each compartment.
• a gas generator of the present invention may be designed to reach maximum inflation or full deployment in the same amount of time as the current, single-stage gas generators. However, compared to previously known gas generators, the generator of the present invention may have a more rapid initial inflation, with a more progressive propellant geometry, followed by a more gradual inflation rate in the subsequent stages. The sequential inflation rates may improve safety to vehicle occupants and/or provide improved final velocity control for the ejection of munitions and submunitions.
• one propellant or gas generant used in a gas generator according to the present invention may include (1) ammonium nitrate as the oxidizer, which is non-toxic and non-corrosive, as opposed to existing airbag propellant formulations, (2) a fuel having a high energy density and high stability, such as CL-20, or other suitable fuels, the characteristics of which will be described below, and (3) a binder such as polycaprolactone (PCL), polyisobutylene (PIB), or glycidyl azide polymer (GAP).
• PCL polycaprolactone
• PIB polyisobutylene
• GAP glycidyl azide polymer
• Fuels that may be used as alternatives to, or in combination with, CL-20 for the fuel of the present invention have comparable or greater values of the following physical characteristics: density, heat of formation, and heat of decomposition.
• a second propellant may include approximately 70-95% energetic nitramine fuel, 5-25% energetic polymer binder and 0.1-5% flash suppressant.
• the generation of hot metal particles e.g., cupric oxide (CuO)
• CuO cupric oxide
• expensive filtering systems as used in current airbag systems, may not be needed.
• coated airbags may be avoided.
• FIG. 1 shows a two-stage gas generator.
• the parts of one embodiment are identified in FIG. 1A and typical dimensions are shown in FIG. IB.
• the parts are shown in FIG. 1C and the dimensions in FIG. ID.
• FIG. 2 shows the deployment of a two-stage gas generator compared to that of a single-stage gas generator.
• FIG. 3 shows a typical single-stage gas generator of the prior art.
• FIG. 4 shows an airbag deploying several submunitions S in a weapon system including gas generator 40 in a spine tube 41.
• FIG. 5 shows an airbag deploying a parachute to decelerate a submunition and to control its speed and trajectory.
• FIG. 6 shows propellant grain configurations: FIG. 6 A - neutral burning, FIG. 6B - progressive burning, FIG. 6C - uniform burning.
• FIG. 7 shows a logarithmic plot of burning rate vs. pressure at various temperatures.
• FIG. 8 shows a representative ignition train
• FIG. 9 shows various ignition systems in FIGS. 9 A-F.
• FIG. 10 shows an electrically operated initiator.
• FIG. 11 shows ignition initiation for different configurations cut into the grain face of the propellants.
• This invention relates to a new type of gas generator.
• This new type of gas generator may be used in various military and commercial applications, such as for example, in airbags used for deploying submunitions, aiming warheads, automobile airbag systems, flotation devices, producing oxygen in oxygen generating devices and other applications.
• These gas generators have at least two chambers, which condition allows the respective gas volumes to be produced under different conditions, i.e., the profile of pressure vs. time for the gas volume produced by each chamber can be different.
• the gas generator can be adapted to the need of the particular application.
• a dual-chamber gas generator can be used, with one chamber being designed to provide an initial very quick, partial deployment of the airbag, when compared to previously known gas generators.
• the second chamber may be designed to provide a second, much slower expansion of the airbag, when compared to previously known gas generators.
• a two-stage gas generator may be used in an automobile airbag system that is designed to activate upon rapid deceleration of the vehicle, such as that which occurs upon impact between an automobile and an object.
• An inertial switch may trigger the gas generator or inflator to deploy an airbag in the system.
• the sequential release of gas from each chamber of the gas generator, and subsequent gradual inflation of the airbag may provide, for example, improved control of the trajectory of a munition or submunition during its horizontal and transitional paths and during its downward free fall.
• FIG. 1 A dual stage, or two-stage, generator according to one embodiment of the present invention is shown in FIG. 1.
• a gas generator 10A is shown in FIG. 1 A.
• two combustion chambers 1 exist within the housing enclosure 2, and are separated by a 3.00-mm thick wall 3.
• Each combustion chamber contains a propellant 4, with both propellants having the same formulations but different geometry.
• Propellant geometry is selected to produce the desired first-stage and second-stage performance.
• Two igniters may be present, one for each combustion chamber.
• the two igniters may be designed to function with a 5-20 ms. difference between the progressive, or quicker or high R Q , burning propellant and the neutral, or slower or low R Q , burning propellant.
• the igniters may include an ignition enhancer 5, which surrounds the initiator 6 and is designed to boost the power of a propellant upon ignition.
• Rupture disks 7 allow the released gas to be funneled into the gas ports 8, where the gas is released.
• Certain embodiments, e.g., a miniature design such as that used in side airbags, may include a slag filter 9.
• the slag filter 9 may be used advantageously as a heat sink, and not necessarily as a particulate filter. The hot gases produced by the gas generator pass through the slag filter and lose heat to the slag filter by conductive heat transfer.
• the slag filter may be coated with a sodium aluminosilicate powder, also known as zeolite, e.g., Zeolite CVB-100.
• zeolite e.g., Zeolite CVB-100.
• the gas generant includes CL-20, GAP, and KNO 3.
• the zeolite coating acts to reduce the gas temperature, thereby reducing the likelihood of burn damage to equipment, as well as premature detonation of the explosive.
• the zeolite coating can also trap harmful gases such as NO x and CO.
• the zeolites may act as molecular traps for larger-size diatomic and polyatomic gases.
• the percent of zeolites used in the slag filter may range from between 1 and 10%, more preferably from between 3 and 1%, and most preferably at 5%, by weight of the filter.
• suitable high-surface-area materials may be used to produce the same result.
• a gas generator for a typical airbag can be quite small.
• the overall dimensions for one airbag can be approximately 85 mm x 44 mm.
• the dimensions of such a typical gas generator 10B are shown in FIG. IB.
• FIGS. 1C and ID a smaller-size or miniature size dual-stage gas generator design is shown.
• Gas generators IOC and 10D are principally the same as those shown in FIGS. 1 A and IB, but they are smaller in size, with less mass of the propellant.
• the partition between the two combustion chambers is aimed at eliminating unnecessary safety concerns, namely preventing propagation to the adjacent combustor port. If one propellant is deployed, the heat produced by the reaction may heat up the propellant in the adjacent chamber, and, upon deploying the second, a severe high pressure may cause the airbag to malfunction.
• the gas generant in each chamber of the dual-chamber gas generator is generally the same, formulation-wise, with each gas generant having a different geometry.
• the gas generants may have a cylindrical, hexagonal, or rosette (the most efficient) geometry, with 37, 19, 7, or 1, perforations, or none at all.
• the second gas generant in the second chamber, as well as any subsequent gas generants in additional chambers may be less progressive with fewer perforations, neutral, or regressive as compared to the first gas generant.
• the ratio of gas generation in the first chamber to that in the second chamber is greater than one.
• the change of pressure as a function of time may be two or more times greater than the change of pressure as a function of time for the gas produced from the second chamber.
• Solid propellants are often divided into two classes, gas generator and rocket motor propellants. This division is based primarily on their energy content.
• Gas generator propellants generally contain ammonium nitrate as an oxidizing agent and have only a small amount or no metallic additives.
• Double-base compositions and those containing nitramines, e.g., RDX, HMX, EDNA, NGU, etc., ammonium perchlorate, etc., as the oxidizer may sometimes be included as a gas generator, as in the case of N-5, the gas generator of the U.S. Army's Wide Area Munition (WAM) reserve battery.
• WAM Wide Area Munition
• Ammonium perchlorate is one of the popular oxidizers for rocket motor propellants; metals such as aluminum are often added to increase the energy content. As the energy content of the propellant increases so does the flame or combustion temperature. Flame temperatures of most gas generator propellants range from 1600° to 3000° F (870° to 1650° C), while rocket propellants generally have flame temperatures that range from 3000° to 6000° F (1650° to 3315° C).
• solid propellants are used that have a flame temperature between 1600° and 3000° F (870° to 1650° C).
• the fuel used may be synthetic rubber, or a plastic selected on the basis of chemical structure, mechanical properties, and processability.
• Some of the materials commonly used are butadiene-acrylic acid, butadiene/methylvinylpyridine, cellulose acetate, nitrocellulose, polyisoprene, and polyvinylchloride.
• the oxidizing agent most commonly used in almost all gas generator propellants is ammonium nitrate. All composite propellants contain additives in one form or another to achieve the desired burning rate, temperature sensitivity, flame temperature, gas output, and physical properties.
• Multibase solid propellants are also used as gas generants. As a matter of fact, this is the type of solid propellant formulation used in the WAM battery gas generator. These, as previously discussed, generally have a higher flame temperature, between 2300° and 3500° F (between 1260° and 1926° C), and have more solid particles in the exhaust. These homogeneous formulations are basically of unstable chemical compounds such as nitrocellulose and nitroglycerin, which are capable of combustion in the absence of all other materials, i.e., they are extremely easy-to-ignite propellants. The most common propellant of this type, sometime referred to as "double-base" propellant, is largely a colloid of nitroglycerin and nitrocellulose.
• Mixing of double-base propellant ingredients may be carried out, for example as in the case of N-5 propellant, by charging raw ingredients to a mixer in a particular sequence to achieve desired properties of the finished propellant.
• Mixers in common usage are horizontal and vertical types, i.e., the axis of rotation of the mixing blades is either vertical or horizontal.
• the action of the blades may thoroughly disperse, mix and incorporate the various ingredients into one homogeneous blend. This mixing may be closely controlled as to rate, or speed of blade rotation, and time. Over-mixing or under-mixing can produce a propellant that does not meet ballistic or physical property requirements.
• Solid propellant grains may be formed by extrusion, as in the case of N-5 propellant, by compression molding, or by casting. Since most propellants are limited by their chemistry to one or two of these methods and since some grain geometries are more suited to one processing method than the other, it is seldom possible to form a particular grain by all the available methods. Therefore, it is necessary to determine whether the specific formulation and shape desired are suited to the processing techniques available. Grains can be machined by equipment found in most well equipped machine shops.
• the energy release rate of a solid propellant gas generator depends greatly on the grain configuration.
• the possible geometric configurations are virtually limitless. Most applications require a relatively constant energy for a time of 20 to greater than 100 seconds, or a short duration of 1 to 10 seconds at a relatively high-energy release rate.
• Typical propellant grain configurations are shown in FIG. 6.
• the end-burning rate or cigarette-burning rate for example as shown in FIG. 6A, is restricted on the diameter and one end, leaving the other end exposed and free to burn uniformly, i.e., undergo neutral burning, for the entire length.
• This configuration is used for the longer duration, low energy release rate.
• the configuration shown in FIG. 6B has restrictor, which is also shown as 114 in FIG. 11, or deterrent applied to all surface of the grain except the inner diameter. When this exposed propellant is ignited, it will burn outwardly, exposing more and more propellant as the flame front progresses. This configuration will produce a progressive energy release rate.
• the grain configuration shown in FIG. 6C has the inner and outer diameter unrestricted.
• the energy release will be of uniform rate; however, the time of burning will be considerably shorter than with the end burner shown in FIG. 6A.
• Many other configurations and special geometries are used to obtain the desired energy release rate. Commonly used geometries may include 7 and 19 perforations, cylindrical granules, which are progressive, and multi-perforated rosette type configurations, which have high efficiency and energy release rate.
• the energy release rate of a propellant grain may reference the start of the ignition cycle to the end [d (dp/dt)/dtj. This rate may also be referred to as the relative quickness (R q ) or vivacity.
• Relative quickness is controlled by propellant geometry, i.e., grain diameter, perforation diameter, web length and the number of perforations. Such propellants are referred to as quick propellants and generate pressures in a closed chamber in fractions of a millisecond.
• Quick propellants almost always require deterrents, or inert material, to slow their burning time to an acceptable safe rate. Such deterrents are applied to the surface of the propellant in one of many coating techniques.
• deterrent coatings examples include, but are not limited to, polyester plasticizer (Paraplex) (Hercote), diethylene glycol dimethacrylate (DEGDMA) and dibutylphathalate (DBP).
• the first two deterrent coatings have proven very effective in reducing the rate of energy release upon ignition of propellant grains. DBP may be less- preferred, however, as it appears to migrate over extended periods of time, in particular at temperatures above 140° F (60° C).
• the coating When propellants are deterrent-coated, the coating normally impregnates the grain throughout, but remains on the surface in relatively higher concentration. This may result in a burning slow-down, i.e., a pressure reduction/control, in the initial stage of the ballistic cycle.
• the coating due to its low molecular weight, migrates to the center of the grain until equilibrium is attained, when equal distribution of the coating is attained throughout the grain.
• the energy release rate is relatively higher than expected leading to LAT failures or higher sigma.
• Propellant burning rate is the rate at which the combustion zone progresses into a mass of propellant, and may be referred to as the mass burning rate. Burning rate is a function of the particular propellant formulation, the chamber pressure, and the propellant temperature. Normally, burning rate, at a specific propellant temperature, may be expressed as:
• burning rate versus pressure is plotted on a logarithmic paper, the curve is a straight line, with the slope of the line as "n" and with "a” as the burning rate intercept at 1 psia or 1000 psia.
• the pressure exponent (n) is not a constant, that is, it may vary at high or low pressures.
• the pressure exponent remains a constant over a limited range of pressures.
• burning rate data may be derived from empirical data or burning rate plots.
• Propellant burning rate is also dependent on the ambient propellant temperature.
• the temperature sensitivity is usually not a constant. It varies with ambient temperature, decreasing at high and low temperatures, hence it is usually given for a specific temperature range; normally 160° to -65° F (71 to -53°C).
• Temperature sensitivity at constant pressure, ⁇ p is given by:
• ⁇ k ⁇ p / (l - n)
• An ignition system that may be used for the present invention may include an electrically actuated initiator, a pyrotechnic or secondary charge, and the propellant grain, as will be described below.
• the initiator ignites the secondary charge, which ignites the propellant grain surface.
• the secondary charge should provide energy over an adequate time to complete ignition of the grain surface and pressurize the gas generator free volume.
• boost is frequently used in identifying the sustaining charge of an ignition system.
• Energy output of the initiator is small when compared to the total energy required for grain ignition, as its function is only to ignite an easily ignitable pyrotechnic material in close proximity.
• Some designs require additional energy during the initial portion of firing to compensate for heat losses into the inert gas generator components; for this, the grain initial burning surface is contoured, through grooves, slots or holes, to provide additional burning surface. This contouring soon burns out leaving the desired burning surface.
• an ignition system In designing an ignition system to meet specified requirements, e.g., for use within embodiments of the present invention, certain parameters may be fixed, or they may be varied, e.g., within narrow limits. Fixed parameters relate to the initiating mechanism for the igniter, type and configuration of the propellant, chamber design, and nozzle or orifice size. Igniter performance, which may be varied to comply with the end-item requirements under the conditions imposed by other design features, may be affected by factors including the following:
• Step 3 is a regressive requirement since thermal equilibrium is approached asymptotically.
• Proper ignition design should, therefore, include the following:
• a fast-burning charge designed to rapidly pressurize the case and burn out on pressurization; and A sustainer that has an energy output that approximates a right triangle as a function of time.
• the sustainer is initiated by the pressurization charge and regresses from a maximum initial output to zero at the point at which thermal equilibrium is attained.
• This ignition system model serves as the basis for design of ignition systems having "smooth" pressure-time characteristics: i.e., rapid pressurization to operating pressure, with no significant peaks, followed by neutral pressure-time curve throughout burning.
• Empirical equations have been developed to estimate the igniter energy requirement. Final tailoring of the igniter may be conducted through ballistic testing of the gas generator system.
• ignition systems consist of the following components: initiator, 91; primer, 92; booster, 93; and sustainer, 94, where the booster and sustainer form the secondary charge.
• initiator 91
• primer 92
• booster 93
• sustainer 94
• type "C” and type "E” ignition systems may be used in certain embodiments.
• Other ignition systems may also be used.
• initiation devices may be divided into two main categories, electrically operated or mechanically operated.
• Electrically operated initiators 100 are either hot wire- or exploding bridge-wire-initiated.
• Mechanically operated initiators are actuated by impact or shock. Electrically operated initiators may be used in preferred embodiments.
• a hot wire initiator may have a resistance wire or element mounted between two electrodes 102, 103. This element may be coated with a low ignition temperature pyrotechnic bead. Electric current flowing through the bridge- wire 101 or element raises the temperature of the pyrotechnic to above its auto-ignition temperature, initiating the pyrotechnic and the remainder of the pyrotechnic train. The resistance of the wire and the ability of the initiator elements to conduct heat away from the pyrotechnic may determine the no-fire and all-fire characteristics of the initiator. High current initiators, e.g., 1 ampere/1 watt to 5 ampere/5 watt, have large heat sinks or heat dissipation ability.
• Exploding bridge- wire initiators are similar to the hot wire type except that a high-energy electric pulse applied across the bridge- wire 101 causes it to vaporize, thereby converting electrical energy into thermal energy and igniting the adjacent pyrotechnic material.
• a gap is often used in the initiator circuitry to provide an open circuit to direct currents; but for a high - voltage pulse this gap is bridged and the resistance wire is exploded.
• FIG. 11 shows the type of saddle that might be expected with various configurations. It shows that, by the proper use of either or both systems, the desired ignition pressure-time curve may be obtained.
• ignition sustainers are often used.
• One type of ignition sustainer may be a small pellet and/or a disc 111 of energetic propellant bonded to the surface of the grain 113. Grooves 112 cut in the grain face provide increased burning surface and aid in obtaining rapid ignition.
• the secondary charge if properly designed, may prevent a "pressure saddle" or momentary lowering of the pressure because of heat losses to the surrounding metal components.
• Selection of an initiator may depend on the means available for providing heat energy to the primary ignition material.
• An electrical current may be applied through a low-resistance, e.g., 0.02 to 5.0 ohms, bridge-wire, imbedded in a heat-sensitive pyrotechnic composition.
• a rule of thumb is that the lower the energy of the solid propellant, the greater the ignition system output required.
• Physical parameters that influence the design of the ignition charge system are free volume, grain configuration, and propellant burning surface. Rapid ignition is assisted greatly by pressurization, but caution should be taken to prevent pressure overshoot during the ignition phase. When determining the requirements for a gas generator system, careful consideration should be given to the ignition system before fixing any physical configuration.
• the more progressive gas generant undergoes rapid ignition and generates sufficient pressure to inflate the airbag to 35-85% of its full capacity, preferably 45% to 85% of its capacity, and most preferably 65%-85% of its full capacity.
• the gas generant in the second chamber provides the remaining inflation of the airbag to achieve an overall internal gas pressure equal to the pressure rated for that airbag for that specific subsystem. That is, when the gas has been completely generated from both chambers of the novel system, the final gas pressure in the airbag is equal to that from the current, one- stage, gas generators.
• the rate of gas generation in the proposed art is controlled by means of providing propellants that generate different rate of gas release. By providing different rates of gas release, the pressure versus time curve would have two slopes for the two-stage system.
• One slope e.g., one corresponding to the first gas generant in the first chamber, could have a very steep slope [(dp) ⁇ /)dt) ⁇ ], while the second slope for the second gas generant could have a less steep slope [(dp) 2 /(dt) 2 .
• the effective time to maximum volume which corresponds to the full deployment of the airbag, would still be the same, but would be controlled in a manner that would prevent a powerful shock to the airbag.
• this performance is advantageous because it may prevent severe accidental mishaps and possible fatalities, which may occur when an airbag deploys in a vehicle moving at speeds over 100 mph (165 km per hour) or deploys into children, light-weight passengers, or passengers who are smoking pipes.
• this performance is advantageous, as it provides improved control over the trajectory and prevents mishaps resulting from radical changes in trajectory that result from currently used airbag systems.
• Embodiments of the present invention may have gas generator systems with even more than two chambers to allow even better control of the pressure vs. time curve, thus enabling the designer to match nearly any pressure vs. time profile.
• raw sodium azide used as the gas-generating composition in most gas generators (for airbag applications), has a relatively high toxicity, which creates handling problems during the manufacturing process. Furthermore, if military personnel or civilians are exposed to remaining portions of the device, toxicity or environmental pollution concerns may need to be considered.
• propellants that are described herein and that may be used in new gas generators according to the present invention are believed to be novel.
• One comprises an oxidizer, a fuel, and a binder that is used to hold the components together.
• An embodiment of a propellant, described herein, has outstanding performance, is more environmentally acceptable than currently used propellants, and does not require the filtration systems currently needed in gas generators.
• the oxidizer is preferably ammonium nitrate, which may constitute approximately 89.5 ⁇ 5.5 % of the propellant.
• the oxidizer should be phase-stabilized to prevent melting and recrystallization to different particle size.
• An example of a suitable phase stabilizer is potassium nitrate (KNO 3 ), which may be present at a concentration of 0.5% to 7% and which may also prevent flash generation; the preferable concentration of the potassium nitrate is 0.5%) to 1%.
• KNO 3 potassium nitrate
• This nitrogen-rich oxidizer when stabilized is insensitive to impact, shock and electrostatic discharge, which makes it safe to handle, to manufacture, and to package.
• the phase-stabilized ammonium nitrate prevents phase transition of the oxidizer during thermal cycling.
• the fuel may constitute approximately 8.4 ⁇ 5.0 % of the propellant.
• Suitable fuels include nearly all nitramines, including CL-20 (C 10 H 2 N 12 O 1 ) (Thiokol Corporation), RDX (C 3 H 6 N 6 O 6 ), HMX (C 4 H 8 N 8 O 8 ), GAP(C 3 H 5 N 3 O) discipline (glycidyl azide polymer, or polycyclidyle azide) (3M Corporation, Minnesota), EDNA (ethylene dinitramine), TATB, LLM-105 and mixtures thereof.
• the preferred fuel is CL-20.
• the binder may constitute approximately 2.1 ⁇ 0.5% of the propellant and acts (1) as a binder to hold components together and (2) to prevent fracture of crystals, which would result in gas generating too fast.
• Suitable binders include polycaprolactone (PCL), polyisobutylene (PIB), polyvinylpyrrolidone and mixtures thereof.
• GAP can be used as a combined fuel and binder. However, its combustion byproducts are toxic and increased amounts of ammonium nitrate are needed to overcome this negative. These higher concentrations of ammonium nitrate make the formulation difficult to process and to ignite.
• a gas generant may include the following: approximately 70-95% of CL-20 energetic nitramine fuel; 5-25% of energetic polyglacidyl azide (e.g., glacidyl azide polymer or GAP) or energetic polymer binder, e.g., polyisobutylene (Vistanex polymer) or PIB; and 0.1-5.0% of a flash suppressant such as potassium nitrate.
• the gas generant may be used in a two-stage gas generator and may be particularly useful for propulsion systems of small, medium and large caliber ammunition.
• ingredients may optionally be added to the formulation. These may include (1) materials to control stability, such as for example ethyl centralite, Akardite I, Akardite II, diphenyl amine, or 2-nitrodiphenyl amine, which may be used at about 0.1-1.0%; (2) materials to control ballistic spikes and high initial pressure rise, a coating material, such as for example ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, allyl methacrylate or Hercote polyester, which may be used at about 0.1 -3.0%; and (3) materials to increase gravimetric density and dissipate static, such as for example graphite, which may be used at about 0.05-1.0%.
• materials to control stability such as for example ethyl centralite, Akardite I, Akardite II, diphenyl amine, or 2-nitrodiphenyl amine, which may be used at about 0.1-1.0%
• materials to control ballistic spikes and high initial pressure rise such as for example ethylene
• the propellant formulation may be processed either as a wet or dry mixture and pressed into tablets, disks or other shapes or extruded into granules.
• Commonly used blending techniques such as those discussed in M.E. Fayed & L. Otten, Handbook of Powder Science and Technology (1984), Emil R. Riegel, Chemical Process Machinery (2 nd Ed. 1960, and Wolfgang Pietsch, Size Enlargement by Agglomeration Ch. 4 (1991), can be used.
• the propellant used in the different chambers may generally have the same chemical composition, but they often differ in geometry, which impacts the rate of burning of the propellant in each chamber. For example, a propellant with more perforations has more surface exposure, which results in faster burning.
• the density of the propellant is also an important indicator of its suitability.
• the preferred density should be approximately 92% or greater than the theoretical density. If the density is too low, not as much propellant can be fit into the chambers. Second, if the density is low, the propellant has a greater likelihood that it will fracture, leading to a different geometry of propellant, which will, as discussed above, have an effect on the burn rate.
• the combustion of the propellant is safe, with the flame temperature of the gaseous products of reaction being less than 120° F (48° C).
• the products of combustion are generally limited to non-hazardous gases, namely water vapor, nitrogen, and carbon dioxide (CO ). These products are not hazardous to the environment. In addition, they are not corrosive, which means that uncoated airbags can be used in the system.
• the amount of propellant in the novel gas generator is much less than is needed in currently used generators. Typically 70-100 gm of propellant is used in the prior art, while 5-8 gm is needed for the novel generator used for deploying submunitions.
• the tank should have a capacity at least as large as the airbag for which the gas generator is used. Any commonly used ballistic test procedures can be used to evaluate the performance of the gas generator.
• the inflator should be capable of producing and/or releasing a sufficient quantity of gas to the airbag within the time limitation required of the air bag systems. Given the time limitation involved in military airbag systems, the airbag should deploy in roughly about 5- 100 milliseconds, depending upon the size of the airbag. Inflators should generally be capable of filling an air bag in these time frames with 15 to 200 liters, depending on the intended application.
• the gas generator receives a signal from an exterior or interior source, and then sends this signal to each initiator.
• the timing of the inflation of the airbag can be triggered by either a trigger signal transmitted to the gas generator, a sensor, such as an infrared (IR) sensor in the submunition that detects targets that match a defined set of IR requirements, a detector such as a direction sensor determining the point in the trajectory, a timer, data programmed into a computer incorporated in the weapon, or other techniques.
• the initiators function sequentially, with a delay, which may be on the order of millisecond(s), between the ignition or activation of each initiator.
• Example 1 A two-stage gas generator A two-stage gas generator is shown in FIG. 1.
• FIG. 1A shows the parts of the generator, while FIG. IB shows representative dimensions.
• the total weight of propellant in this system is approximately 5 to 10 gm.
• a smaller design is shown in Fig. 1C, with corresponding, representative dimension being shown in Fig. ID.
• Embodiments shown in FIG. 1 may be used, for example, in airbag systems for deploying submunitions or in airbag restraint systems in automobiles.
• thermochemical simulation program written in FORTRAN.
• the program shows the theoretical, thermochemical performance of the gas generant.
• the output shown lists, among other things, the expected theoretical density, the reaction temperature inside the chamber, the ratio of specific heats (shown as gamma), and the energy or impetus. It also lists the expected byproducts of combustion in moles, wt%, mole%, and volume%. The output values shown are based on 100 grams of propellant.
• Example 3 Submunition deployment A munition system is assembled by surrounding a rocket with submunitions.
• An airbag may be inserted between the rocket and the submunitions.
• the system also includes a gas generator having at least two chambers. When the system is in the vicinity of the intended target(s), the gas generator becomes operational and inflates the airbag, thus deploying the submunitions.
• the gas generator can inflate the airbag in a more predictable fashion than the one-chamber gas generator. This means that the submunitions will be deployed closer to the intended target.
• Example 4 Using an airbag to control the trajectory of a submunition. Once the submunition of Example 3 is beginning its downward trajectory, an airbag connected to a parachute P on the submunition is inflated in order to deploy the parachute P. See FIG. 5A.
• This gas generator 50A has two or more chambers, and there is better control over the deployment of the parachute and, therefore, the trajectory of the submunition vs. earlier systems containing only one chamber in the gas generator.
• the parachute reduces the speed of the submunition and also balances it during its horizontal, transitional path and its downward freefall.
• An alternative to the parachute is the use of the airbag itself to provide buoyancy to the submunition. See FIG. 5B.
• the airbag is attached to the submunition and, when inflated, acts like a balloon-type object.
• This airbag is inflated by the gas from the gas generator 5 OB and, rather than providing drag, which is provided by the parachute, the airbag provides buoyancy, which also impacts the trajectory of the submunition.
• FIG. 5B where the parachute P is replaced with an airbag A, shown as a balloon-like object, which is inflated by the gas generator 5 OB.
• a gas generator can be used to propel ammunition. Instead of gunpowder being used in ammunition casing, a gas generator can be used.
• the gas generator can be enclosed in a separate component, e.g., plastic or ceramic, placed in the muzzle before the ammunition.
• the gas generator can be loaded into the barrel 59 of the weapon, with no need for a casing, as shown in FIG. 5C, with gas generator 50C and projectile 58.
• the amount of gas generant needed to propel munitions can be calculated using well-known formulas, which relate the amount of gas generant to the pressure generated and to the velocity of the munition. For example:
• the M919 cartridge is a 25mm, armor piercing, fin stabilized, discarding sabot, with tracer.
• the first chamber of a typical two-chamber gas generator might generate 8-20% of the total amount of gas needed to inflate the airbag within, e.g., 10 milliseconds.
• the preferred fraction of the gas from the first chamber is 10-15%), and the most preferred amount is 15% of the total amount of gas needed.
• the ignition system for the second chamber should ignite approximately at the end of the gas generation from the first chamber, and the rate of inflation from that chamber should control the final activity for which the airbag is used. For example, a rate combined burn time for both the first and second stage of, preferably, between 60 and 90 milliseconds is needed to eject the submunitions from a munition or to deploy a parachute to control the trajectory of a submunition.

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• Combustion & Propulsion (AREA)
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• Organic Chemistry (AREA)
• Air Bags (AREA)
• Feeding, Discharge, Calcimining, Fusing, And Gas-Generation Devices (AREA)

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• 2003
  • 2003-09-10 JP JP2004536442A patent/JP2005538834A/ja active Pending
  • 2003-09-10 WO PCT/US2003/028373 patent/WO2004024653A2/en active Application Filing
  • 2003-09-10 EP EP03752198A patent/EP1539657A2/en not_active Withdrawn
  • 2003-09-10 AU AU2003270501A patent/AU2003270501A1/en not_active Abandoned
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