Patent Application
20110057429
The present invention relates generally to gas generating systems, and to autoignition compositions employed in gas generator devices for automotive restraint systems, for example.
The present invention relates to autoignition compositions that upon ignition provide the flame front and pressure front necessary to safely ignite gas generant compositions in combustible communication therewith. As known in the art, gas generators are typically provided with an autoignition composition that in the event of a fire ignites responsive to a desired threshold temperature. As a result, the gas generant is ignited prior to melting for example, thereby safely igniting the main gas generant composition to inhibit or prevent the likelihood of an explosive event once the gas generant begins to combust.
An ongoing challenge is to simplify the manufacture of a gas generator by reducing the constituents required in the production thereof. For example, in many gas generators used in vehicle occupant protection systems, several discrete compositions are provided to serve correspondingly discrete functions. These compositions often include a primary gas generating composition that when combusted is employed to provide sufficient quantities of gaseous products to operate the associated restraint device, such as an airbag or seatbelt pretensioner. A booster composition is utilized to elevate the pressure and heat within the gas generator prior to combustion of the primary gas generant, thereby creating favorable conditions within the inflator for acceptable combustion of the primary gas generant. Of course, still yet another composition is the auto-ignition composition employed to provide safe combustion of the other compositions in the event of a fire. The auto-ignition composition is designed to ignite at temperatures below the melting point of the primary gas generant for example, thereby ensuring the controlled combustion of the primary gas generant, as opposed to an explosive reaction perhaps.
The use of potassium chlorate within an autoignition composition has been considered given the autoignition properties of this oxidizer. Furthermore, carboxylic acid in combination with potassium chlorate typically provides a desired autoignition temperature of 200 degrees Celsius or less. Nevertheless, these types of compositions typically do not provide anything but auto-ignition function when employed in gas generators used in vehicle occupant protection systems, for example. As known in the art, gas generating systems may be used for providing a supply of inflation or actuation gas to a gas-actuated element of a vehicle occupant protection system. An ongoing challenge is to simplify the manufacture of a gas generating system by reducing the size, weight, and number of constituents required in the production thereof. For example, in many gas generators used in vehicle occupant protection systems, several discrete compositions are provided to serve correspondingly discrete functions. These compositions often include a primary gas generating composition that when combusted provides sufficient quantities of gaseous products to operate an associated restraint device, such as an airbag or seatbelt pretensioner.
While each separate composition contributes to efficient and effective operation of the gas generating system, each composition also adds weight, cost (in materials and assembly time), and volume to the system. For example, to facilitate operation of each composition and to prevent mixing between the various compositions, the booster composition, gas generant, and autoignition compositions are typically stored in separate tubes or chambers. Provision of a separate storage chamber for each composition generally adds to the weight, cost, and assembly time needed to construct the gas generating system. In addition, if a relatively greater the amount of combustible material is burned during operation of the system, a correspondingly greater amount of effluent and heat will be usually generated by the burning of the material. Therefore, it would be advantageous to reduce the number of gas generating system components and the number of compositions used in the operation of the system.
The above-referenced concerns and others may be resolved by gas generating systems including an autoignition composition containing a first oxidizer selected from metal chlorates, such as potassium chlorate, a carboxylic acid or dicarboxylic acid as a primary fuel, a secondary oxidizer selected from metal and nonmetal nitrates, nitrites, oxides, basic metal nitrates, and other known oxidizers, and a secondary fuel selected from azoles including tetrazoles, triazoles, and furazans, and salts thereof. Other constituents including extrusion aids, such as fumed silica and/or graphite, may be included in relatively small amounts.
In further accordance with the present invention, a gas generator devoid of a booster composition tube, and a vehicle occupant protection system incorporating the gas generator are also included.
Compositions useful in the present invention contain a first oxidizer selected from alkali, alkaline earth, and transitional metal chlorates, and mixtures thereof, such as potassium chlorate, at about 10-60 weight %; a primary fuel selected from carboxylic acids and dicarboxylic acids, such as DL-tartaric acid, at about 15-45 weight %; a secondary oxidizer selected from metal and nonmetal nitrates, nitrites, oxides, and other known oxidizers at about 30-50%; and a secondary fuel selected from tetrazoles, triazoles, furazans, and salts thereof at about 0-30 weight %, said weight percent calculated with regard to the weight of the total composition. Extrusion aids or processing additives such as graphite or fumed silica may be added in relatively smaller amounts, such as 0.1-2% by weight of the total composition for example.
The present compositions contain a metal chlorate such as potassium chlorate; a primary fuel selected from carboxylic acids and dicarboxylic including DL-tartaric acid, L-tartaric acid, D-tartaric acid, succinic acid, glutamic acid, adipic acid, mucic acid, fumaric acid, oxalic acid, galactaric acid, citric acid, glycolic acid, L-malic acid, and compounds having at least one —COOH— group, and mixtures thereof; a second fuel selected from an azole including tetrazoles, triazoles, furazans, salts thereof, and mixtures thereof; a secondary oxidizer selected from metal and nonmetal nitrates or other known oxidizers not containing a perchlorate. The carboxylic acid or dicarboxylic acid will preferably have a primary hydrogen or PKA less than or equal to 3. Nevertheless, it has been found that with certain fuels/salts, the pKa of the base acid may range up to 5.0 or less.
In one embodiment, the total fuel constituent including the carboxylic fuel and the second fuel is provided at about 20-45% by weight of the total composition; the oxidizer constituent is provided at about 20-50% by weight of the total composition; and the potassium chlorate or metal chlorate is provided at about 10-60% by weight of the total composition wherein the weight percent of the chlorate is separately calculated from that of the oxidizer. The composition may be formed by wet or dry mixing the constituents in a granulated form in a known manner, and then pelletizing or otherwise forming the composition for further use. The constituents may be provided by Fisher Chemical, Aldrich Chemical, GFS, and other known suppliers.
Compositions that may be employed in the present inventive inflators are exemplified by the following Examples:
A known autoignition composition was prepared by homogeneously mixing dried and granulated D-glucose at about 26.875 wt % and potassium chlorate at about 73.125 wt %, the percents stated by weight of the total composition. The composition autoignited at about 144 C as measured by DSC analysis. The propellant formed from the constituents resulted in an approximate 55.5% gas yield. The impact sensitivity of this formulation had an HD50 of 2.0 inches as conducted in conformance with the Bruceton Test.
An exemplary formulation was provided that functions as a booster, an autoignition, and a gas generant composition. The formulation contains 5-aminotetrazole at about 19.0 wt %, DL-tartaric acid at about 20.0 wt %, strontium nitrate at about 35.0 wt %, and potassium chlorate at about 26.0 wt %. The constituents were previously and separately ground to a relatively small size in a known manner. They were then dry-mixed to form a substantially homogeneous composition. The composition autoignited at about 140 C as measured by DSC analysis. The propellant formed from the constituents resulted in an approximate 67% gas yield. The impact sensitivity of this formulation had an HD50 of 11.5 inches as conducted in conformance with the Bruceton Test. The composition was aged for about 480 hours at 107 C and still autoignited at about 145.1 C as determined by DSC analysis.
An exemplary formulation was provided that functions as a booster, an autoignition, and a gas generant composition. The formulation contains 5-aminotetrazole at about 19.0 wt %, DL-tartaric acid at about 19.0 wt %, strontium nitrate at about 50.0 wt %, and potassium chlorate at about 12.0 wt %. The constituents were granulated and dry-mixed to form a substantially homogeneous composition. The composition autoignited at about 141 C as measured by DSC analysis. The propellant formed from the constituents resulted in an approximate 68.2% gas yield. The impact sensitivity of this formulation had an HD50 of 8.8 inches as conducted in conformance with the Bruceton Test. As shown in
An exemplary formulation was provided that functions as a booster, an autoignition, and a gas generant composition. The formulation contains DL-tartaric acid at about 28.0 wt %, strontium nitrate at about 32.0 wt %, and potassium chlorate at about 30.0 wt %. The constituents were previously and separately ground to a relatively small size in a known manner. They were then dry-mixed to form a substantially homogeneous composition. The composition autoignited at about 153 C as measured by DSC analysis. The propellant formed from the constituents resulted in an approximate 66.1% gas yield. The impact sensitivity of this formulation had an HD50 of 8.1 inches as conducted in conformance with the Bruceton Test.
As indicated in Examples 1-4, compositions formed in accordance with the present invention (Examples 2-4) preferably autoignite at or below about 180 C and provide a booster function as well. The compositions of the present invention may also produce substantial quantities of gas, and exhibit sufficient burn rates thereby producing sufficient amounts of gas when activated. Compositions employing a secondary oxidizer, such as strontium nitrate, provide relative increased quantities of gas and an improved sensitivity. A Bruceton sensitivity result wherein H50=3.9 or more relaxes the packaging requirements as per U.S.D.O.T regulations. Accordingly, compositions having a sensitivity result of 3.9 or greater provide substantial packaging advantages. It will further be appreciated that the use of a secondary fuel, such as 5-aminotetrazole, in conjunction with the carboxylic or dicarboxylic acid, the secondary oxidizer, and the potassium chlorate produces greater amounts of gas, acceptable autoignition temperatures, and booster functionality. As such, compositions formed in this manner may be provided to singularly replace the three discrete booster, autoignition, and primary gas generant compositions normally found in a gas generator.
As shown in Table 1 below, the various acids shown, when converted to salts and mixed with potassium chlorate in stoichiometric amounts exhibit acceptable autoignition temperatures for a variety of uses. Certain autoignition temperatures exceed 180 C but may still be useful in selected applications such as hybrid inflators and seatbelt pretensioners for example. It will be appreciated that these Examples reflect the autoignition character imparted by the resulting salts and the potassium chlorate. As further shown, acids exhibiting a pKa of about 3.05 or less generally provide autoignition temperatures generally less than 170-180 C. However, acids exhibiting a pKa of about 5.0 or less may still be acceptable wherein autoignition temperatures of 250 or so are acceptable, for example. It will be appreciated that certain acids such as citric acid and malonic acid when stoichiometrically combined with potassium chlorate may not satisfy the autoignition function, but still when combined with at least a second oxidizer function as a booster oxidizer and a primary gas generant. It has further been determined that the use of a desiccant as described in co-owned and co-pending U.S. Ser. No. 11/479,493, herein incorporated by reference, may in certain circumstances maintain optimum environmental conditions within the gas generator thereby facilitating the tri-functionality of the composition when used as an autoignition, booster, and primary gas generating composition.
It will be appreciated that in further accordance with the present invention, gas generators made as known in the art and also vehicle occupant protection systems manufactured as known in the art are also contemplated. As such, autoignition compositions of the present invention are employed in gas generators, seat belt assemblies, and/or vehicle occupant protection systems, all manufactured as known in the art.
In yet another aspect of the invention, the present compositions may be employed within a gas generating system. For example, as schematically shown in
Extrusion aides may be selected from the group including talc, graphite, borazine [(BN)3], boron nitride, fumed silica, and fumed alumina. The extrusion aid preferably constitutes 0-10% and more preferably constitutes 0-5% of the total composition.
The compositions may be dry or wet mixed using methods known in the art. The various constituents are generally provided in particulate form and mixed to form a uniform mixture with the other gas generant constituents.
It should be noted that all percents given herein are weight percents based on the total weight of the gas generant composition. The chemicals described herein may be supplied by companies such as Aldrich Chemical Company for example.
As shown in
Referring now to
Referring again to
Safety belt assembly 150 may also include (or be in communication with) a crash event sensor 158 (for example, an inertia sensor or an accelerometer) including a known crash sensor algorithm that signals actuation of belt pretensioner 156 via, for example, activation of a pyrotechnic igniter (not shown) incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and 6,419,177, previously incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner.
It should be appreciated that safety belt assembly 150, airbag system 200, and more broadly, vehicle occupant protection system 180 exemplify but do not limit gas generating systems contemplated in accordance with the present invention.
System 10 includes an outer housing 12 and an inner housing 14 positioned within the outer housing and containing a quantity of gas generant material 16 therein. Inner housing 14 defines a combustion chamber for the gas generant. Inner housing orifices 18 provide fluid communication between the interior and exterior of inner housing 14. A fluid flow path is provided within housing 12 and between orifices 18 and gas exit openings 20 formed in an end or other portion of housing 12. A booster chamber 22 is formed by a booster cup 23 and a divider 28. Chamber 22 houses a booster composition 24 therein. Divider 28 separates booster composition 24 from gas generant 16 and enables fluid communication (via opening 28a) between the booster chamber and the combustion chamber upon activation of the gas generating system and combustion of the booster composition. As used herein, the term “booster chamber” is understood to designate any structure and/or components which perform the function of separating the booster composition from the gas generant composition. An initiator 32 is provided for initiating combustion of booster composition 24 upon receipt of an activation signal, in a manner known in the art. An autoignition material 30 is positioned so as to provide or enable fluid communication with the booster composition 24 upon exposure of the system to an elevated external temperature (such as that produced by a fire, for example) sufficient to cause ignition of the autoignition material.
The present description is for illustrative purposes only, and should not be construed to limit the breadth of the present invention in any way. Thus, those skilled in the art will appreciate that various modifications could be made to the presently disclosed embodiments without departing from the scope of the present invention as defined in the appended claims.
This application claims priority to and is a continuation-in-part of co-pending and co-owned U.S. application Ser. No. 11/497,149 having a filing date of Jul. 31, 2006 (originally claiming the benefit of U.S. Provisional Application Ser. No. 60/703,998 filed on Jul. 29, 2005), and, this application also claims priority to and is a continuation-in-part of co-pending and co-owned U.S. application Ser. No. 11/906,348 filed on Oct. 1, 2007 (originally claiming the benefit of U.S. Provisional Application Ser. No. 60/848,682 filed on Sep. 30, 2006).
| Number | Date | Country | |
|---|---|---|---|
| 60703998 | Jul 2005 | US | |
| 60848682 | Sep 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11497149 | Jul 2006 | US |
| Child | 12924521 | US | |
| Parent | 11906348 | Oct 2007 | US |
| Child | 11497149 | US |
