Package making – Methods – With contents treating
Reexamination Certificate
1998-12-24
2001-05-22
Gerrity, Stephen F. (Department: 3721)
Package making
Methods
With contents treating
C053S079000, C053S127000, C053S403000, C073S040700, C073S049300, C141S003000, C250S303000, C280S741000
Reexamination Certificate
active
06233908
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to pressurized fluid-containing devices such as used in the inflation of inflatable devices such as inflatable vehicle occupant restraint airbag cushions and, more particularly, to the introduction of a leak trace material, particularly a radioactive leak trace material, into such pressurized fluid-containing devices.
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, the 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.”
The above-referenced prior U.S. patent application Ser. No. 08/935,016 relates that various inflator devices have been disclosed in the art and that it is common for various such inflator devices, or at least particular components thereof, to be checked for the presence or occurrence of undesired leaks. In particular, one category of inflator devices is often referred to as “compressed gas inflators” and refers to various inflators which contain compressed gas. One 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. In a second type of compressed gas inflator, commonly referred to as a hybrid inflator, inflation gas results from a combination of stored compressed gas and the combustion of a gas generating material, e.g., a pyrotechnic.
Compressed gas inflators commonly require the presence of at least certain specified quantities of the particular compressed gas material in order for the inflator to perform in the designed for manner. In such inflators, it is generally desired that the amount(s) of stored compressed material(s) be maintained in the inflator within at least a certain specified tolerance in order to ensure proper operation of the inflator. While proper inflator operation can be variously defined, ultimately an inflator and associated airbag cushion need provide adequate vehicle occupant protection over an extended period of time (typically 15 years or more) subsequent to original construction and installation in a particular vehicle. Thus, beyond the simple functioning of the inflator and deployment of an associated airbag cushion, such inflatable restraint systems desirably operate or function in a manner wherein the airbag cushion will deploy, when needed, in the desired and proper manner.
While there are various methods to determine the rate of leakage from a compressed gas inflator, in practice, a typically preferred method relies on the incorporation of helium as a tracer gas in the particular compressed gas mixture. In such a method, helium will constitute a certain fraction of the stored gas composition which escapes from the inflator. (As will be appreciated and dependent on the specific situation, the exact fraction of helium detected as a result of a leak may be equal, less than, or greater than the helium fraction of the stored compressed gas. The physics associated with these various situations, however, is generally beyond the scope of the present discussion. Typically, however, these different situations are dependent on certain, particular factors such as the magnitude of the leak, the total pressure within the storage vessel, as well as the initial gas composition, for example.)
The rate of helium leakage from a pressure vessel is normally detected using a mass spectrometer system. For this specific practice, the mass spectrometer is normally calibrated or designed to detect the presence of helium in the gases constituting the sample. The utilization of helium as a leak trace material is advantageous in several respects:
First, as the normal or typical atmospheric content of helium is rather low, the background helium level (or residual helium in the environment such as that surrounding the detection apparatus) is normally correspondingly low. As a result, the possibility of a corresponding mass spectrometer being falsely influenced and possibly producing a spurious signal is significantly reduced or minimized.
Second, the signals of a mass spectrometer for at least certain different molecular species can be nearly the same. Consequently, a mass spectrometry signal produced or resulting from the presence or occurrence of one molecular species may interfere or mask a mass spectrometer signal produced or resulting from the presence or occurrence of a different molecular species. For example, the molecular weights of nitrous oxide and carbon dioxide are approximately 44.02 and 44.01, respectively. As a result, it is generally very difficult to distinguish between these molecular species via mass spectrometry. Helium, however, with a molecular weight of 4, produces a mass spectrometry signal that is relatively easily distinguishable from the signal correspondingly produced by other potentially present species.
Third, helium is a relatively small, low molecular weight monatomic gas, facilitating the passage thereof through even relatively small or narrow leak paths. Thus, such use of helium may facilitate or better permit detection of even relatively small or narrow leak paths.
Conventional helium leak detection techniques may, however, suffer or potentially suffer from a number of problems or possible disadvantages. For example, in order to permit a leak check or determination of the relatively small range of leakage which may normally be acceptable for commercial airbag inflator devices, it is commonly necessary to include a relatively large amount of helium in the associated compressed gas mixture. In practice, the amount of helium required is generally dependent on factors such as the magnitude and type of leak, the design life of the inflator, and the criteria for adequate performance for the inflator as a function of time. However, the incorporation of even moderate amounts of helium within a compressed gas inflator is or can be disadvantageous as such inclusion can, for a given volume, significantly increase the storage pressure of the corresponding inflator contents. Conversely, at a given pressure, the storage volume of an inflator will need to be increased in order to accommodate the mass of the so added helium.
A significant limitation on the use of helium in such leak detection schemes is that unless the helium concentration within the vessel is known, the leak rate from an inflator pressure vessel normally cannot be accurately checked at a date substantially later than the date the inflator was manufactured. That is, unless the leak is of the type that the compressed gases (e.g., both the primary stored gas and the helium tracer gas) are escaping in equal proportion to that at which they were loaded (as in the original composition), then the leak rate determination will normally be in error. Since knowledge of the type of leak cannot be definitively known a priori, the making of such an assumption can result in significant error. Moreover, if a pressurized vessel is returned at a later date for the leak rate to be reevaluated, a helium leak rate determination may be inaccurate.
An additional possible limitation or drawback to the use of such helium leak detection techniques is that the occurrence or presence of liquid materials within the storage vessel may impede or “mask” the helium. For example, if a liquid with a relatively high surface tension is present in the vessel, such liquid could possibly flow into a hole through which gas would normally leak and may, at least temporarily, inhibit the passage of the gaseous material out of the inflator. However, with time, the liquid may no longer occupy the leak path and the stoppage of gas leakage therethrough may only be temporary.
In
Green David J.
Rink Karl K.
Young Anthony M.
Autoliv ASP Inc.
Brown Sally J.
Gerrity Stephen F.
LandOfFree
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