This invention relates generally to an apparatus, commonly referred to as an inflator, for use in inflating an inflatable device such as an inflatable vehicle occupant restraint of a respective inflatable restraint system. More specifically, the invention relates to relates to such inflation devices and related methods which utilize or rely at least in part on a pressurized fluid such as a compressed gas. In particular, the invention relates to such devices and related methods which self-compensate, at least in part, for certain design requirements associated with one or more of the manufacture, production, storage and long-term use of such a device.
It is well known 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 systems, an airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. 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 inflating an inflatable restraint system airbag cushion. One category of such inflator devices is often referred to as "compressed gas inflators" and generally refers to various inflator devices which contain compressed gas.
As is known, one particular type of compressed gas inflator, commonly referred to as a "stored gas inflator," simply contains a quantity of a stored compressed gas which is selectively released to inflate an associated airbag cushion.
Another known type of compressed gas inflator is commonly referred to as a "hybrid" inflator. In such an inflator device, inflation gas results from a combination of stored compressed gas and the combustion of a gas generating material, e.g., a pyrotechnic. Hybrid inflators that have been proposed heretofore have been subject to certain disadvantages. For example, such inflators commonly result in the production of a gas having a relatively high particulate content. The removal of such solid particulate material, such as by the incorporation of various filtering devices within or about-he inflator, undesirably increases the complexity of the inflator design and processing and can increase the costs associated therewith.
In view of these and other related or similar problems and shortcomings of prior inflator devices, a new type an inflator, called a "fluid fueled inflator," has been developed. Such inflators are the subject of commonly assigned Smith et al., U.S. Pat. No. 5,470,104, issued Nov. 28, 1995; Rink, U.S. Pat. No. 5,494,312, issued Feb. 27, 1996; Rink et al., U.S. Pat. No. 5,531,473, issued Jul. 2, 1996, Rink et al., U.S. Pat. No. 5,803,492 issued Sep. 8, 1998 and Rink et al., U.S. Pat, No. 5,836,610, issued Nov. 17, 1998, the disclosures of which are fully incorporated herein by reference.
Such inflator devices typically utilize a fuel material in the form of a fluid, e.g., in the form of a gas, liquid, finely divided solid, or one or more combinations thereof, in the formation of an inflation gas for an airbag cushion. One form of the fluid fuel inflator utilizes a compressed gas. In one such inflator device, the fluid fuel material is burned to produce gas which contacts a quantity of stored pressurized gas to produce inflation gas for use in inflating a respective inflatable device.
Beyond the simple functioning of an inflator and deployment of the associated airbag cushion, proper operation of and performance by an inflatable restraint system generally requires that the inflator operate and the airbag cushion deploy in a proper and desired manner. While proper inflator operation can be variously defined, ultimately an inflator and the associated airbag cushion need provide adequate vehicle occupant protection over an extended period of time (typically 15 years or more) after original construction of the vehicle. For example, one common technique by which the performance of an inflator device may be evaluated involves the monitoring of the pressure achieved upon discharge of the inflator device into a closed tank of known volume, sometimes referred to as the "tank pressure." In using such performance evaluation technique, it is commonly desired that after a service life of about 15 years or more, an airbag inflator device be able to produce or achieve a tank pressure of at least about 90% of the tank pressure value obtainable when the inflator device was in an original or new condition or state.
The satisfaction of such inflator performance criterion generally requires or necessitates that an inflator device associated with a particular airbag cushion satisfy at least certain design requirements. For example, compressed gas inflators commonly require the presence of at least a certain specified quantity of the compressed gas material in order for the inflator to perform in the designed-for manner. The quantity or amount of stored compressed material in an inflator is generally at least a function of the quantity or amount of the material originally placed within the inflator device or a specific chamber thereof (sometimes referred to as the "load" or "fill") as well as the ability of the inflator device or specific chamber thereof to contain or maintain a selected quantity or amount of the stored compressed material therein (sometimes referred to in term of the "leak rate" therefrom). In practice, it is common to speak of such leak rate and load design parameters in terms of acceptable or desirable corresponding tolerances.
As will be appreciated, the ability of an inflator device to withstand or tolerate a greater or higher leak rate is generally desirable from a manufacturing perspective. For example, measurement and monitoring of lower or lesser leak rates generally requires the use of more sensitive and typically more expensive measurement equipment and techniques.
In the manufacture or production of compressed gas inflator, the load or fill tolerance of compressed gas is commonly one of the most difficult requirements to be satisfied. In practice, compressed gas inflators and, more particularly, the pressure chambers thereof, are typically designed for a selected or maximum storage pressure. As will be appreciated, greater or larger storage pressures generally necessitate that the walls of the gas storage chambers of such inflators be relatively thicker for increased strength. The combination of large volume and thick walls may result in an inflator design of greater than desired weight and/or bulk.
Moreover, load and leak rate tolerances are commonly or frequently interrelated. For example, the need to provide a sufficient leak rate tolerance to facilitate leak rate measurement and monitoring may severely limit or restrict the range of acceptable load variation or tolerance. As will be appreciated, precise compressed gas loading can be difficult and costly to achieve.
Thus, there is a need and a demand for a compressed gas-containing inflator design and associated methods which minimize, reduce or avoid the criticality of at least one or more design parameter associated therewith, such as relating to the load tolerance, the leak rate tolerance and combinations thereof for a particular inflator device.