BACKGROUND OF THE INVENTION
This invention relates generally to vehicular occupant restraint and, more particularly, to pressure activated restraint system devices as well as related or associated methods of gas generation and compositions used in such gas generation.
Vehicular occupant restraint systems that include or incorporate actuatable restraint devices are known in the art. In such systems, the restraint device is typically actuated upon the occurrence of a condition during which a vehicle occupant is to be restrained. An example of a condition for which a vehicle occupant is customarily desired to be restrained is a vehicle collision.
One well-known type of actuatable restraint system seeks to protect a vehicle occupant using a cushion or bag, e.g., an “airbag cushion,” that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such inflatable restraint systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Such systems typically also include one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden decelerations of the vehicle and to electronically trigger activation of the system. Upon actuation of the system, the cushion begins to be inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as an “inflator.”
Many types of inflator devices have been disclosed in the art for the inflating of one or more inflatable restraint system airbag cushions. Inflator devices which form or produce inflation gas via the combustion of a gas generating material, i.e., a “gas generant,” are well known. It is also known that certain of such inflator devices may use such generated gas to supplement stored and pressurized gas by the addition of high temperature combustion products, including additional gas products, produced by the burning of the gas generating material to a supply of the stored, pressurized gas. In some cases, the combustion products produced by the burning of a gas generating material may be the sole or substantially the sole source for the inflation gas issuing forth from a particular inflator device.
It is common that inflator devices include an initiator, such as a squib, and an igniter. For example, common initiator devices used in such applications include: bridgewire, spark-discharge, heated or exploding wire or foil, through bulkhead (e.g., an initiator which discharges through a bulkhead such as in the form of a metal hermetic seal), and may, if desired, optionally contain a desired load of a suitable pyrotechnic charge. In practice, upon receipt of an appropriate triggering signal from a crash or other selected deceleration sensor, the initiator activates causing the rapid combustion of the igniter material, which, in turn, ignites the gas generant, such as in the form of tablets or wafers. In typical such inflator devices, it is common that a squib is used to ignite an igniter composition which is usually present in a separate compartment or canister. In this manner, the igniter material is generally physically separated from both the squib and the gas generant. In some cases, however, the igniter material may be present as a coating such as applied directly onto the gas generant tablets or wafers with an electrically actuated squib still being used to ignite the igniter material. In such case, though the igniter material is physically joined or in contact with the gas generant, both the igniter material and the gas generant are physically separated from the squib components. Very seldom, if ever, is a granular igniter composition physically mixed with gas generant tablets or wafers to effect ignition thereof.
Commonly desired features or performance criteria for inflatable restraint system igniter compositions include:
1. ignitability via typical squib charges such as by means of primary explosives such as zirconium/potassium perchlorate or lead trinitroresorcinate, for example;
2. upon combustion, having a high heat of explosion;
3. ease and safety of manufacture and production;
4. exhibit minimal or reduced ignition delays, e.g., ignite a gas generant composition within an inflator device within about 10 milliseconds, preferably within about 8 milliseconds or less and, even more preferably, at least in certain applications, within about 5 milliseconds or less; and
5. produce or result in relatively low levels of various undesirable effluent gases such as nitric oxide (NO), ammonia (NH3) and carbon monoxide (CO), for example.
Typical igniter compositions used in such applications are composed of a metallic fuel and selected oxidizer. Common useful metallic fuels for such compositions include boron, zirconium, titanium and silicon, for example. Typical or common oxidizers used in such compositions include alkali metal perchlorates, chlorates and nitrates. One such igniter formulation common or standard for use in airbag inflators is composed of about 15 to about 30 weight percent (typically about 25 weight percent) boron and about 70 to about 85 weight percent (typically about 75 weight percent) potassium nitrate. In the art, this standard igniter formulation is commonly referred to as “BKNO3.”
Unfortunately, typical igniter compositions, such as BKNO3, are generally deficient in one or more of the above-identified criteria. Further, such typical igniter compositions may commonly burn at very high combustion temperatures, such as temperatures of up to about 3000 K. Also, the gas fraction produced by reaction of such igniter compositions is generally relatively low.
Another type of vehicular actuatable occupant restraint system has or includes a seat belt which is extendable across a vehicle occupant and includes an actuatable device, such as a pretensioner, provided to move at least a portion of the seat belt relative to the occupant. For example, one modem seat belt is known as a 3-point restraint because it is secured to the vehicle at three points arranged about the vehicle occupant to provide a diagonal torso section and a horizontal lap portion to hold the vehicle occupant in the seat. The belt is customarily attached to the vehicle by a spring-loaded retractor tending to tighten in the belt, and by a buckle for quick release of the belt. Seat belt pretensioners are typically sited at the retractor or at the buckle end of the restraining seat belt. Seat belt pretensioners are commonly designed to store energy which, when released, effects the pretensioning operation. This energy may be mechanical energy in the form of a stressed spring, but more modern pretensioners are commonly pyrotechnically operated. Pyrotechnically operated pretensioners comprise a sealed tube containing a gas generant composition which reacts rapidly to generate gas which expands rapidly to provide the energy to effect the pretensioning operation. For example, such generated gas may be used to drive a piston or the like, such as included or used in a pretensioner, in association with a seat belt or other restraint device. In view of the relatively small amount of gas generated or produced from or in such devices, as compared to gas generating inflators typically used in the inflation of inflatable restraint system airbag cushions, such devices are commonly referred to as “micro-gas generators.”
Micro-gas generators are generally composed of a single housing which contains an initiation element such as in the form of squib, an intermediate igniter composition and a high output, gas generating material. Squibs used in such devices typically include a heated bridgewire to which has been applied a thermally sensitive very hot burning initiator composition however, other known initiation elements can, if desired be used. Thus, micro-gas generators are typically very small devices which generally contain the components of an airbag inflator, including an initiation element, igniter composition and a high output, gas generating material without the degree of physical separation typically present in airbag inflators. Further, due to the very small operating time requirements associated with micro-gas generator applications (such as operating times of about 6 milliseconds or less), such devices generally contain a much larger ratio of igniter material to gas generating material, as compared to typical airbag inflator devices. For example, inflators used in association for inflation of frontal impact airbag cushions employed for driver protection typically contain or include igniter material in a range of about 3-10% by weight of the total gas producing material (e.g., igniter material and gas generating output charge) present in the inflator device. In contrast, in micro-gas generators, the igniter material may generally be present within the device in a relative amount of at least about 20% by weight of the total gas producing material present therewithin and typically in a range of about 20-50% by weight of the total gas producing material present in the device.
Commonly assigned, Barnes et al., U.S. Pat. No. 6,132,480, issued Oct. 17, 2000, whose disclosure is hereby incorporated by reference, discloses an igniter composition for a gas generant in airbag inflation applications and related methods of gas generation. The igniter compositions and methods of gas generation of this patent include a boron fuel component (e.g., about 10 to about 25, preferably about 15 to about 20 composition weight percent), an oxidizer component (e.g., about 55 to about 80 composition weight percent) and a gas-producing fuel component, such as guanidine nitrate, (e.g., at least about 10 to about 25, preferably about 15 to about 25 composition weight percent).
While such igniter compositions and related methods of gas generation are generally effective in alleviating at least some of the concerns or overcoming at least some of the problems of inflatable restraint system igniter compositions, further improvements are desired or required for at least certain particular applications. For example, a desirable feature of micro-gas generator devices used in or in connection with seat belt pretensioners is the production of a relatively large quantity of gas from a relatively small volume. In addition, it is desirable that such gas generator devices minimize or avoid the production of substantial amounts of possibly undesirable effluent gases such as carbon monoxide and nitric oxide, for example, and which undesirable effluent gases might somehow escape into the vehicle interior and thus come into contact with the occupant(s).
Thus, there is a need and a demand for improvements in igniter compositions and related methods of gas generation such as desired or suitable for use in occupant restraint system devices such as micro-gas generators such as in the form of a seat belt pretensioner. In this regard, there is a particular need and demand for such igniter compositions, related methods of gas generation and corresponding occupant restraint system devices which are preferably effective in minimizing or reducing ignition delays, e.g., ignite a gas generant composition within an occupant restraint system device within about 1 millisecond, preferably within about 0.25 milliseconds or less and, even more preferably, at least in certain applications, within a delay time on the order of about 0.1 milliseconds, while also minimizing or avoiding the production of various undesirable effluent gases such as nitrous oxide (N2O), nitric oxide (NO), ammonia (NH3) and carbon monoxide (CO), for example.
SUMMARY OF THE INVENTION
A general object of the invention is to provide an improved igniter composition and method of generating gas suitable for use in gas generation in connection with a motor vehicle occupant restraint system such as a micro-gas generator such as a seat belt pretensioner or the like.
A more specific objective of the invention is to overcome one or more of the problems described above.
The general object of the invention can be attained, at least in part, through an igniter composition which includes a fuel component containing at least about 3 composition weight percent and less than 15 composition weight percent of boron and an oxidizer component containing at least one oxidizer material selected from the group consisting of alkali metal nitrates, alkaline earth metal nitrates and mixtures thereof. In accordance with a preferred embodiment of the invention, the fuel component and the oxidizer component are present in stoichiometrically balanced amounts.
The prior art generally fails to provide igniter compositions and methods of generating gas suitable for use in gas generation in connection with a motor vehicle occupant restraint system such as a micro-gas generator such as a seat belt pretensioner or the like, which igniter compositions and gas generation methods minimize, avoid or otherwise desirably prevent formation or generation of significant amounts of incomplete products of combustion, such as carbon monoxide.
The invention further comprehends an occupant restraint system device which includes a housing containing a supply of reactant material. In accordance with a preferred embodiment of the invention of such aspect of the invention, such a reactant material includes a fuel component containing at least about 3 composition weight percent and less than 15 composition weight percent of boron and an oxidizer component containing at least one oxidizer material selected from the group consisting of alkali metal nitrates, alkaline earth metal nitrates and mixtures thereof, wherein the fuel component and the oxidizer component are present in stoichiometrically balanced amounts. Particular embodiments relating to this aspect of the invention include a seat belt pretensioner and a micro-gas generator, for example.
The invention still further comprehends a method of generating gas suitable for use in an occupant restraint system of a motor vehicle. Such a method involves igniting a supply of a specified igniter composition to form igniter composition reaction products and contacting a supply of a gas generant composition with the igniter composition reaction products to form product gas. In accordance with one preferred embodiment of the invention, the igniter composition contains a fuel component containing at least about 3 composition weight percent and less than 15 composition weight percent of boron, and an oxidizer component containing at least one oxidizer material selected from the group consisting of alkali metal nitrates, alkaline earth metal nitrates and mixtures thereof. Further, the fuel component and the oxidizer component are desirably present in such a composition in stoichiometrically balanced amounts.
As used herein, references to a specific composition, component or material as a “fuel” are to be understood to refer to a chemical which generally lacks sufficient oxygen to bum completely to CO2, H2O and N2.
Correspondingly, references herein to a specific composition, component or material as an “oxidizer” are to be understood to refer to a chemical generally having more than sufficient oxygen to burn completely to CO2, H2O and N2.
References to “stoichiometrically balanced amounts” of fuel and oxidizer components in a composition are to be generally understood to refer to those compositions which include or contain components in sufficient relative amounts such as to minimize or avoid the production of significant amounts of incomplete products of combustion such as CO and NO, for example. More particularly, as used herein, a fuel component and the oxidizer component are considered present in stoichiometrically balanced amounts if the composition contains no more than about ±4 weight percent of the amount of fuel (other than boron) and oxidizer required for complete burning to CO2, H2O and N2.
Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawing.