VARIABLE OUTPUT AIRBAG INFLATOR

Abstract: A multi-stage airbag inflator (10) is operable initially, when activated, to cause an airbag to deploy slowly and then, after a delay, to deploy rapidly, includes a housing having at least first and second chambers of preferably different size, separated by a bulkhead (40). Preferably one chamber is smaller since it can be used to produce a smaller amount of gas to cause an initial slow deployment of the airbag. A gas generant charge is ignited in the first chamber (30), and after some delay, a gas generant charge in the second chamber (32) is ignited. The multi-stage inflator can be used to provide the varying inflation rates needed to adjust the inflation of airbags to accommodate the severity of the crash and the position of a vehicle occupants.

Description: VARIABLE OUTPUT AIRBAG INFLATOR The present invention relates to gas generators or mflators, for inflating vehicle restraint cushions, commonly known as a rbags . Airbags have been used for some time to provide impact protection to occupants of motor vehicles. More particularly, this invention relates to an improved inflator that can provide varying rates of inflation of the airbag. The rate of airbag inflation can be controlled through the inventive inflator to adapt to various crash conditions and/or occupant positions. In airbag systems there is typically a cushion or bag which, m a crash, is inflated to provide protective cushioning to the vehicle occupants. To inflate the airbag such systems employ an inflator to produce inflation gas. Various mflators operating upon different principles are known. For each operating principle, there is a slight difference m performance such as the rise and fall of pressure m the cushion over time. As such, for different applications, mflators operating on different principles are preferred. For airbag systems to be effective they must be activated at the moment of crash and a proper inflating time is an absolute necessity. On the other hand, if the airbag inflates too rapidly, the passenger may be injured by the inflating airbag. To prevent such injury by the inflating airbag, it is necessary that the inflating speed of the bag be controlled. Therefore, a multi-stage airbag device has been proposed m order to satisfy these contradictory requirements as described above . The multi-stage airbag device works such that the airbag is inflated to a predetermined level during the initial stage of the crash and after a brief interval it is inflated completely. With such a multi-stage airbag device, the chances of injury to an out-of-position vehicle occupant can be reduced and a wider range of crash conditions can be accommodated. The time intervals between the initial stage deployment and the subsequent stage deployments are set m relation to the quantity of gas used m the first stage and other factors. However, an improper interval adversely affects the airbag as a safety device. For example, if the interval is too short, it may cause injury, but if the interval is too long, the shock absorption action of the airbag will be weakened and may result injuries to the vehicle occupant. For this reason, a high degree of precision is required for the delayed ignition signal generator whose function it is to activate the first gas generant and thereafter the second and third gas generant . A typical delayed ignition signal generator is made up of complex electronic circuitry. Because of the complexity of the system and the attended high cost, its applicability to such infrequently used devices such as airbags, is limited. While such adaptive systems are desirable, they typically require additional components on the inflator. Further, it is even more difficult to provide an adaptive pyrotechnic inflator that will meet the size requirements for vehicles, especially for driver side and side impact applications. Numerous approaches have been suggested for adaptive airbag systems. For example, US 4 998 751 discloses a two-stage automotive airbag inflator that comprises an elongated housing with a bulkhead located the housing which separates two beds of pyrotechnic gas generant. The bulkhead of the US 4 998 751 inflator is perforated and the inflator uses two igniter tubes. US 4 998 751 also teaches that the igniters are different m that they have different burn rates and that a fuse runs between the two-igniter tubes. US 5 368 329 discloses a dual stage inflator where the surface area of the gas generant wafers is increased by shattering the wafers through the use of a dual function squib. US 5 400 487 discloses a variable inflation system for airbags that uses a processor for selecting which of a plurality of gas generators will be individually initiated to provide optimal protection to the occupant. The processor m conjunction with acceleration sensors and occupant position sensors determines the number of gas generant beds to be ignited and the delay between each firing. US 5 564 743 discloses a multiple stage airbag inflator system wherein the inflator housing contains two separated chambers, each containing gas generating material and an ignition system. The wall tnat separates the two chambers has a frangible section designed to rupture m response to a predetermined level of gas pressure m one of the chambers, thus providing fluid communication between the chambers. US 5 630 619 discloses a hybrid adaptive inflator for airbags. While the present invention is not concerned with hybrid mflators, this patent does teach the use of two pressure vessels and pyrotechnic heating devices m each pressure vessel . The two vessels are connected to a central chamber that comprises burst discs. US 5 630 619 is representative of the state of the art m adaptive inflator design. US 5 765 866 discloses an airbag inflator comprising a metal housing, a knitted wire filter, stainless steel burst foils and a gas generant composition that contains from 5 to 25 weight % mica. US 5 765 866 fails to suggest a multi-stage inflator that contains at least two chambers that have different volumes and amounts of pyrotechnic gas generant . There is provided m accordance with the attacheα claim 1 and the claims dependent thereon an adaptive, multi-stage pyrotechnic inflator that reliably provides gas to a motor vehicle's airbag over a large range of crash situations For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference is made to the accompanying drawings and descriptive matter m which preferred embodiments of the invention are illustrated. Brief Description of the Drawings Fig. 1 is a perspective view of the exterior of an embodiment of an inflator according to the invention; Fig. 2 is a cross sectional view of an inflator according to the invention taken along line 2 - 2 of Fig.l; Fig. 3 illustrates a number of pressure-time curves from the firing of the inventive inflator with time delays between the firing of the first chamber and the second chamber varying from 0 to 25 micro seconds; and Fig. 4 is a cross-sectional view of a three chambered inflator according to the invention. Detailed Description of the Invention With reference to Fig. 1, an embodiment of an inflator according to the invention is generally designated by reference numeral 10. The inflator 10 includes first and second ends 12,14. While various forms are possible, such a spherical, cubic and the like, it is preferred that the inflator have a generally cylindrical shape. The inflator has exit portals 16, 18 placed about its circumference. Exit portals 16 are associated with the first chamber (not shown) while exit portals 18 are associated with the second chamber (not shown) . The inflator 10 also has two electrical connectors that are associated with two discreet igniters (one for each combustion chamber) , a first electrical connector 20 for the first igniter and a second electrical connector (not shown) at the second end 14. With reference to Fig. 2, which is the inflator 10 of Fig. 1 cross section, taken along the line 2-2 of Fig. 1. There is shown a generally cylindrical inflator with a first end 12 and a second end 14. Each end has an electrical connector 20 for receiving an electrical signal when the inflator is to be fired. The connectors 20 are in association with squibs 21 that ignite the enhancer compositions 22. In the event of a crash, an electronic module (not shown) delivers an electrical impulse to the selected squib which lights an ignition train, which in turn lights the gas generant pellets 28. The connectors 20 supply electrical current to the squibs . The squibs comprise a filament that ignites the enhancer composition. The enhancers 22 may be any of a number of known compositions that are readily ignited by the squibs and burn at a high rate and temperature. The gases and hot burning particles from the ignited enhancer 22 exit through portals 24 the enhancer housing 26. The gas and particles then ignite the gas generant pellets 28 m the first combustion chamber 30 and/or the second combustion chamber 32. The gases produced by the burning enhancer and the gas generate pellets then pass through a pellet retention plate 34. The retention plates may comprise a metal plate with numerous holes drilled through it, a screen or a sheet of expanded metal. The retention plate 34 simply retains the pellets m the combustion chambers 30, 32 and allows for the essentially unrestricted movement of the gas from the combustion chambers 30, 32 to the first fllter g/coolmg chamber 36 and the second flltermg/cool g chamber 38. The two flltermg/coolmg chambers 36, 38 are separated by a solid bul nead 40. The bulkhead 40 is placed along the axis of the inflator 10 to provide for equal or different volumes m the first and second chambers. It should be unαerstood that the term chamber includes the combustion chamber and the flltermg/coolmg chamber wherein the bulkhead 40 separates the two chambers . Depending upon the actual service requirements of the inventive mflator, the first chamber may be from 20 to 80% of the total inflator volume. In a more preferred embodiment, the first chamber is 55-75% of the total mflator volume. In similar fashion, the first combustion chamber may contain from 20 to 80% of the total amount of the gas generant composition, more preferably from about 55 to 75% and most preferably from about 55 to about 65%. In embodiments where there are three or more chambers, the gas generant may be divided equally among the chambers or unequally, depending upon the design requirements of the mflator. The gases after passing through the filtration/coolmg chambers 36, 38 exit the mflator 10 at exit portal 16 for the first chamber and exit portal 18 for the second chamber. The interior of the exit portals are preferably covered with a foil 42 such as aluminum or stainless steel foil to prevent the incursion of water vapor. This foil 42, sometimes referred to as a "burst foil" is typically of a thickness of from 0.01 to about 0.20 mm. The foil is typically adhered to the interior wall of the filtration/coolmg chamber through the use of an adhesive. The filtration/coolmg chambers 36, 38 are filled with any heat absorbing material such as knitted wire, ceramic beads, metal shavings and the like. The heat absorbing material serves to reduce the temperature of the generated gas and to trap any slag or particulate matter produced during the combustion of the gas generant 28. The mflator 10 can be constructed of any metal such as steel and aluminum. The mflator is preferably constructed of steel and can be cast or milled into the various components as illustrated m Fig. 2 and then assembled through the use of welds 46. Preferably, the welds are created by an inertia welding process similar to that known m the industry. Fig. 3 is a graphical representation of a number of firings of one embodiment of the inventive mflator. Inflators as illustrated m Fig .2 were prepared as described below and ignited m a sixty liter tank fitted with a pressure transducer. The solid lines indicate the tests where the smaller chamber was fired first followed by a time delay of 0, 10, 15 or 20 milliseconds before igniting the larger chamber. The dashed lines represent the tests where the larger chamber was fired first, followed by a t me delay of 10, 15, 20 or 25 milliseconds before firing the smaller chamber. With reference to Fig. 4, and the description provided for Fig. 2, an embodiment of an mflator, cross-section, according to the invention is generally designated by reference number 60. The inflator 60 includes first and second ends 12, 14 respectively, and a third end 54. In this configuration, the inventive multi-stage mflator is "T" shaped with the generally cylindrical shapes of each chamber intersecting at a bulkhead 40. The third end 54 has exit portals 48 placed about the circumference of the third filtermg/coolmg chamber 50. The flator 60 has three electrical connectors 20 associated with three discrete igniter assemblies 44 (one for each combustion chamber) . The method of operation is identical to that described for Fig. 2, except that a third combustion chamber 52 and a third filtermg/coolmg chamber 50 are present. As disclosed previously, the combustion chambers 30, 32 and 52 may contain equal amounts of gas generant pellets 28, or, preferably unequal amounts. In this embodiment, the third combustion chamber 52 contains an amount of gas generant that is less than the first combustion chamber 30 and more than the second combustion chamber 32. In similar fashion, the volume and therefore the amount of the media m the third coolmg/filtration chamber 50 is preferably different from the other two coolmg/filtration chambers 36, 38. A solid bulkhead 40 separates each of the coolmg/filtration chambers 36, 38 and 50. In operation, the inventive mflator is connected to a controller (not shown) which produces appropriate electrical signals upon sensing a crash. Depending upon the severity of the crash, and other factors such as the position of a passenger m the seat, the controller will cause one or more of the igniter squibs to fire. The time delay between the firing of the chambers and the order of firing will also be calculated by the controller. In this manner, the amount of gas fed to the cushion may be varied to inflate the cushion to varying "hardness" , or to create different pressure levels over time the cushion or to address the "second impact" crash situation. As disclosed above, the two or more combustion chambers may contain the same amount of gas generant or different levels of gas generant. For example, the first chamber may generate 70% of the total gas volume and the second chamber may comprise 30% of the total volume. It thus becomes apparent that the flator 10 may be modified for various applications and provide a wide variety of outputs. It is an aspect of the present invention to provide a new and improved multi-stage airbag mflator system that functions optimally over a wide range of crash situations. It is another aspect of the present invention to provide a new and improved multi-stage airbag mflator. It is yet another aspect of the present invention to provide a new and improved multi-stage airbag mflator having controllable performance characteristics to provide multiple level energy absorptive capabilities. The foregoing and other aspects and advantages of the present invention are accomplished m a new and improved multiple stage airbag flator system having an mflator including a housing having gas discharge ports m direct communication with an airbag to be inflated. The housing includes at least two separated chambers, each containing a quantity of gas generating material for producing gas and an ignition system therefor for rapidly inflating the airbag. The housing has an internal impermeable wall (bulkhead) forming the separated chambers . The ignition system in one or more chambers is activated to provide a selected amount of gas for inflation of the airbag. Also, a time delay means is included the system for activating the multiple ignition systems m response to an identified crash type . Referring to Fig. 2, an mflator 10 was constructed of steel using conventional techniques and equipment. Welds 46 where placed at the junction of the various parts after filling the combustion chambers 30, 32 with pellets of a non-azide gas generant. Representative gas generant compositions useful m the inventive flator housing include fuels such as the alkali metal azides, ammotetrazoles, tetrazoles, bitetrazoles, tπazoles, the metal salts thereof, guanidme nitrate, ammoguanidme nitrate and mixtures thereof; combination with an oxidizer such as the alkali and alkaline earth metal nitrates, chlorates, perchlorates, ammonium nitrate and mixtures thereof . A preferred gas generant comprises a mixture of nitroguanidme and ammonium nitrate. Typically, the gas generant or gas producing material can comprise about 15 to about 70 weight % fuel, about 2 to about 80 weight % oxidizer and about 1 to about 30 weight % other materials, such as coolants and processing aids. The gas generant can be formed into various shapes using various techniques known to those skilled m the art. It is desirable to pelletize the gas generant composition. To do so, up to about 5.0 weight %, typically 0.2-5 weight % of a pressing aid or binder may be employed. These may be selected from materials known to be useful for this purpose and include molybdenum disulfide, graphite, elastomers, polyesters, boron nitride, silicon dioxide, talc, calcium stearate and clays . The gas generant composition may optionally contain a catalyst at up to about 3 weight %, typically between about 1 and about 2 weight % . Copper chromate and malorie blue (a ferro-ferric cyanide) are representative combustion catalysts. In these test mflators and with reference to Fig. 2, the first combustion chamber 30 contained 35 grams of generant pellets 28. The second combustion chamber 32 contained 25 grams of the generant pellets 28. The squibs 21 are connected by electrical connectors 20 to a sensor means (not shown) which detects a vehicle crash. The sensor initiates a firing signal which activates one or both of the squibs 21, which ignites the enhancer composition 22 which m turn, ignites the gas generating composition 28. A controller (not shown) determines which squib to fire first and the time delay (if any) between the firing of the squibs and therefore the two combustion chambers. The igniter assembly 44 is attached to the mflator housing through any useful means and is preferably attached via a weld 46. As used herein, a "squib" is understood to be any device that will initiate the first fire m the combustion tram and may be, for example, an electrical device having two electrodes insulated from one another and connected by a bridge wire. The bridge wire is preferably embedded m one or more layers of a pyrotechnic material designed to give a flash of heat of sufficient intensity to ignite the enhancer composition 22. Those skilled m the art will understand that various electrical, electronic, mechanical and electromechanical initiators, such as a semi-conductor bridge initiator, can be used m the present invention. The gas generant 28 is ignited by the very hot gases and particles that are generated by the combustion of the enhancer composition 22, which exit the igniter assembly portals 24. The resulting ignition of the gas generant results m the production of gases which pass through the pellet retainer 34 and then through the coolmg/filtration chambers 36, 38. In general, the gases generated upon the ignition of gas generant pellets 26 pass through the pellet retainer 34 and proceed m a direction essentially parallel to the axis of the chamber while passing through the filtration/coolmg media contained within the filtration/coolmg chambers 36, 38. The gases, upon impacting the bulkhead 40, are forced to turn ninety degrees and exit through the apertures 16, 18 after rupturing the burst foils 42. The cooling /filtration chambers 36, 38 are filled with a filtration/coolmg media such as ceramic chips, metal chips or preferably knitted wire. The Knitted wire is preferably made of stainless steel, however, low carbon steel may be used. The combustion gases, after passing through the coolmg/filtration material exit the mflator housing 10 at exit portals 16, 18. A number of exit portals 16, 18 can be varied and are spaced about the circumference of the housing at the end of the coolmg/filtration chambers distal to the combustion chambers. The exit portals 16, 18 are preferably sealed with a foil 42, preferably stainless steel burst foil, on the inside of the housing. When the pressure inside the chambers 36, 38 exceeds a given value, the foils rupture and the gases escape the mflator through apertures 16, 18 which then inflate the airbag (not shown) . EXAMPLE I Testing of Inflator Eight mflators substantially as described above and m Fig. 2 were constructed wherein the smaller combustion chamber contained 25 grams of ammonium nitrate/nitroguanidme gas generant pellets. The larger chamber was filled with 35 grams of gas generant. Compressed knitted 304-stamless steel wire (0.023") was placed m the coolmg/filtration chambers; 25 grams m the smaller chamber and 50 grams m the larger chamber. The enhancers contained 2 and 4 grams of a conventional enhancer composition, respectively. The assembled mflators were evaluated m a sixty liter test tank fitted with equipment to record the pressure and time profile. The mflators were installed into the tank and ignited. The resulting pressure versus time curves are found m Fig. 3. These data clearly indicate that the inventive mflator can provide a broad range of pressures at a given point m time. For example, using the dual chambered mflator according to the invention, a pressure of from 125 to 300 kPa can be delivered at 20 milliseconds (ms) post ignition. This range of pressures can be accomplished through firing the smaller chamber first and then firing the larger chamber 20 ms later for the low pressure of 125 kPa and by firing both chambers simultaneously for the high pressure of 300 kPa. EXAMPLE II Particulate and Gas Analysis Three mflators were assembled as described m Example I and were evaluated m a 100 cubic foot test chamber. This test is designed to simulate the interior volume of the standard automobile. Gas analysis and particulate analysis is also possible using this test. The test equipment consisted of a 100 cubic foot steel chamber containing a steering wheel simulator. To the chamber was attached a vacuum pump, a bubble flow meter, filters and a Fourier Transform Infrared Spectrophotometer (FTIR) . The mflator was attached to the simulated steering wheel assembly within the chamber, the chamber was sealed and the gas generant ignited. Gas samples were analyzed using the FTIR at zero time (background) at a 1 , 5, 10, 15 and 20 minute intervals from ignition. Airborne particulate production can also be measured using the 100 cubic foot test chamber by filtering post-ignition air from the chamber through a fine filter and measuring the weight gained by the filter. The airborne particulate was collected using a single stage collection device. The quantity of airborne particulate was determined using an analytical balance. Post-analysis particulate filters were dried for two hours at 104°C to determine the level of water or volatile materials in the filters. No detectable mass loss was observed. Table 1 contains the results from this testing. Two 25 ms delay tests were run and one 15 ms delay. In all three experiments, the large chamber was fired first. TABLE 1 Airborne Particulate Effluent Data * Filter was not use n t is t me interval The gas samples were also analyzed for ammonia, benzene, carbon dioxide, carbon monoxide, formaldehyde, hydrogen chloride, hydrogen cyanide, methane, nitric oxide, nitrogen dioxide, sulfur dioxide and water vapor using the FTIR. Samples were transferred directly to the FTIR via six feet of inch OD fluoropolymer tubing. Table 2 contains the gaseous effluent results . TABLE 2 (5aseous Eff luent Toxicity Resu ts Ammo Ben Carbon Carbon Formalde Hydrogen Hydrogen Methane Nitric Nitrogen Sulfur Water nia zene Dioxide Monoxide hyde chloride Cyanide Oxide dioxide dioxide Vapor Analysis Method FTIR FTIR FTIR FTIR FTI FTIR FTIR FTIR FTIR FTIR FTIR FTIR Detection Limit (pp ) 5 5 50 10 2 2 2 5 2 0.5 5 500 Analysis Delay (min) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 1 6 <5 1292 600 <2 <2 <2 12 2 0.8 <5 7833 5 8 <5 1555 694 .2 <2 .2 15 3 1.1 <5 8779 EXAMPLE A 10 8 <5 1532 689 ^ 2 <2 <2 1 <2 0.9 <5 8828 15 7 5 1526 683 .' ^ o 15 2 0.9 <-5 8620 20 8 5 151? 6 n 0 11 p 0 9 • 5 8385 TWA 20* 8 <5 1508 677 <2 ^ 15 <2 0.9 <5 8599 1 <5 <5 1308 614 2 <2 <2 9 <2 <0.5 <5 7032 5 <5 <5 1531 700 2 <2 <2 11 2 <0.5 <5 8659 EXAMPLE B 10 6 <5 1548 694 < 2 <2 <2 11 2 <0.5 <5 8485 U3 15 7 -5 1499 683 ■- 2 <2 <2 11 2 <0.5 <-5 8216 20 8 <5 1482 675 2 <2 <2 11 <2 <0.5 <5 7997 TWA 20 <5 <5 1497 682 <-2 <2 2 11 <2 <0.5 <5 8238 1 <5 <5 1333 645 ■' 2 <2 -2 13 3 <0.5 <5 6110 5 < S <5 1528 707 2 . o 2 1 i 3 <0.5 <5 7037 EXAMPLE C 10 6 <5 1508 689 « ^ 2 <2 <2 13 3 <0.5 <-5 6749 15 8 <5 1493 686 <2 <2 <2 13 4 <0.5 <5 6626 200 9 <5 1491 692 2 <.2 13 3 <0.5 <5 6510 TWA 20 <5 <5 1488 688 - 2 <2 v 13 3 <0.5 <5 6686 *TWA _ 20 - 11 me wei ghted average a 20 mi nut s

Claims: 1. A multi-stage airbag mflator (10) comprising: a housing divided into at least two chambers that are adjacent to each other and separated by an impermeable bulkhead (40) ; (b) a first combustion chamber (30) containing a solid gas producing material provided m one of the at least two chambers; (c) a second combustion chamber (32) containing a solid gas producing material provided m another one of the at least two chambers; (d) a first ignition means (21) for igniting said gas producing material m the first combustion chamber (30) ; (e) a filter/coolmg chamber (36) associated with said first combustion chamber (30) ; (f) a second ignition means (21) for igniting said gas producing material m said second combustion chamber (32) ; (g) a filter/coolmg chamber (38) associated witn said second combustion chamber (32) , and (h) apertures (16, 18) m said first and second filter/coolmg chambers (36, 38), wherein said apertures are sealed with a foil (42) . 2. The multi-stage airbag mflator (10) according to claim 1 wherein said foil (42) is stainless steel foil. 3. The multi-stage airbag inflator (10) according to claim 2 wherein said stainless steel foil (42) is of a thickness of 0.091 to 0.20 mm, said foil further characterized by an adhesive on at least one surface of said foil . 4. The multi-stage airbag inflator (10) of claim 1 wherein said gas producing material comprises 15-70 weight % of a fuel and 2-80 weight % of an oxidizer. 5. The multi-stage airbag inflator (10) of claim 4 wherein the fuel is selected from alkali metal azides, alkaline earth metal azides, aminotetrazoles and the metal salts thereof, tetrazoles and the metal salts thereof, bitetrazoles and the metal salts thereof, triazoles and the metal salts thereof, nitroguanidine , guanidine nitrate, nitrates and mixtures thereof. 6. The multi-stage airbag inflator (10) of claim 4 wherein the oxidizer is selected from transition metal oxides; alkali metal nitrates, chlorates and perchlorates; alkaline earth metal nitrates, chlorates and perchlorates; ammonium nitrate and mixtures thereof. 7. The multi-stage airbag inflator (10) of claim 1 wherein said apertures (16, 18) are placed along the circumference of said inflator. 8. The multi-stage airbag inflator (10) of claim 1 wherein the inflator consists of two chambers. 9. The multi-stage airbag inflator (10) of claim 1 wherein said apertures (16, 18), said bulkhead (40) and said combustion chambers (30, 32) are in a positional relationship that requires the gases generated by said solid gas producing material to impact upon said bulkhead and change direction before exiting said apertures.

Inventors: BOWERS DONALD, CANTERBERRY J B, SOLOMON DANIEL STEVEN, BOWERS, DONALD, CANTERBERRY, J., B., SOLOMON, DANIEL, STEVEN
Applicants: BREED AUTOMOTIVE TECH, BREED AUTOMOTIVE TECHNOLOGY, INC.
Application year: 2000
Main classification: B60R21
IPC codes: B01J7, B60R21, C06B31, C06B35, C06B43, C06D5