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.
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 sometimes decompose given their hygroscopicity or tendency to absorb moisture. Unsuccessful attempts have been made to inhibit moisture retention or uptake within these compositions without adversely affecting the desired autoignition temperature.
The above-referenced concerns are resolved by gas generating systems including an autoignition composition containing an alkali metal Chlorate, such as potassium chlorate, a carboxylic acid as a fuel, and a desiccant or moisture retaining material combined with the oxidizer and fuel. Other constituents including extrusion aids, such as flamed silica and/or graphite, may be included in relatively small amounts.
In further accordance with the present invention, a gas generator and a vehicle occupant protection system incorporating the autoignition system are also included.
The present compositions contain an alkali metal chlorate oxidizer such as potassium chlorate at about 25-75%. and more preferably about 40-60%, by weight of the total composition, a carboxylic acid as a fuel at about 25-75%, and more preferably about 30-40%, by weight of the total composition, and a desiccant at about 5-35%, and more preferably about 10-30%, by 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. It has been found that the decomposition typically identified in other potassium chlorate/carboxylic acid compositions that are employed as autoignition compositions is mitigated or eliminated by including a desiccant in the autoignition composition.
The present compositions contain a chlorate such as an alkali, alkaline earth, or transitional metal chlorate; a fuel selected from DL-tartaric acid, carboxylic or dicarboxylic acids, or compounds having at least one —COOH— group; a second fuel selected from an azole including tetrazoles, triazoles, and furazans; an oxidizer selected from metal and nonmetal nitrates or other known oxidizers not containing a perchlorate. The carboxylic acid will have a primary hydrogen or PKA less than or equal to 3.
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 30-50% by weight of the total composition; and the potassium chlorate or metal chlorate is provided at about 10-20% 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 palletizing or otherwise limning the composition for further use. The constituents may be provided by Fisher Chemical, Aldrich Chemical, GFS, and other known suppliers.
Carboxylic acids may be selected from the group including tartaric acid and its isomers, succinic acid, glutamic acid, adipic acid and mucic acid, and mixtures thereof DL-tartaric acid is particularly preferred.
An exemplary formulation is provided that functions as s booster and an autoignition composition. The formulation utilizes 5-aminotetrazole, DL-tartaric acid, strontium nitrate, and potassium chlorate. The propellant formed from these constituents results in an approximate 67% gas yield. The impact sensitivity of this formulation has an HD50 of 11.5 inches.
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.
Carboxylic acids may be selected from the group including tartaric acid and its isomers, succinic acid, glutamic acid, adipic acid, and mucic acid, and mixtures thereof. DL-tartaric acid is particularly preferred. The present compositions may also include processing additives such as flow agents and lubricants common in the art such as fumed silica and graphite. The desiccant may be any material that will absorb or react with water to remove it from the other components in the autoignition mixture. Exemplary desiccants are activated or hydrated calcium sulfate (DRIERITE®), clay, silica gel, calcium oxide, and zeolites or molecular sieves. Zeolites, as shown in the tables, are particularly effective in assuring an autoignition temperature at or below 200 C, and also in minimizing the mass differential of an autoignition composition before and after heat aging as defined below. All compositional constituents are available from Sigma-Aldrich, or other known suppliers.
The oxidizer generally contains potassium chlorates, but may also contain one or more other alkali metal chlorates.
Accordingly, autoignition compositions of the present invention typically perform at optimum levels, even after standard heat aging of over 400 hours.
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, 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 156 (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.
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 is a continuation-in-part of co-pending and co-owned U.S. application Ser. No. 11/479,493, having a filing date of Jun. 30, 2006, which in turn claims the benefit of U.S. Provisional Application Ser. No 60/695,925 tiled on Jun. 30, 2005.
Number | Date | Country | |
---|---|---|---|
Parent | 11479493 | Jun 2006 | US |
Child | 14336666 | US |