Land vehicles – Wheeled – Attachment
Reexamination Certificate
2001-02-21
2004-03-23
Dickson, Paul N. (Department: 3618)
Land vehicles
Wheeled
Attachment
C280S741000
Reexamination Certificate
active
06709011
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to inflatable safety restraint systems for vehicles. More specifically, the present invention relates to a novel apparatus and method for improving leak detection in an inflator for an airbag assembly.
2. The Relevant Technology
The inclusion of inflatable safety restraint devices, or airbags, is now a legal requirement for many new vehicles. Airbags are typically installed in the steering wheel and in the dashboard on the passenger side of a car. In the event of an accident, an accelerometer within the vehicle measures the abnormal deceleration and triggers the release of pressurized gases. The expanding gases fill the airbags, which immediately inflate in front of the driver and passenger to protect them from impact against the steering and dashboard components. Side impact airbags have also been developed in response to the need for similar protection from impacts in a lateral direction, or against the side of the vehicle.
The pressurized gas typically originates within a pressure vessel called an “inflator.” Inflators provide the pressurized gas in many different ways. Some inflators, termed “stored gas inflators,” simply store the gas in a high-pressure state, and open to release the gas during impact. “Pyrotechnic” inflators, by contrast, do not store gas; rather, they contain generants that, upon ignition, react to produce the gas. “Hybrid” inflators utilize compressed gas in combination with pyrotechnics to produce the inflation gas. In some instances, the pyrotechnic can also serve to open the inflator to permit the gases to escape.
Each type of inflator must generally be sealed. In the case of compressed gas inflators, it is necessary to keep the compressed gas from escaping. For pyrotechnic and hybrid inflators, the generants must typically be sealed off from ambient air to avoid degradation from moisture and other contaminants. Inflators utilizing solid generants are typically activated by an initiator, which converts an electric impulse to heat in order to ignite the charge.
Such initiators often have electrical contacts, or prongs, protruding from the inflator to receive the electric impulse from wiring or a socket within the vehicle. Consequently, an opening must be provided in the wall of the inflator so that the prongs can extend outside the pressurized compartment(s) of the inflator. In order to ensure that the generant remains viable, a membrane, or pressure dome, may be positioned around the initiator to separate the generant from the initiator and whatever ambient air may be present in the vicinity of the initiator. The pressure dome is designed to disintegrate upon activation of the initiator, thereby permitting the heat of the initiator to reach the generant.
Upon disintegration of the pressure dome, the cavity is then exposed to the gases created by the reaction of the generant. Directly after ignition of the generant, these gases are hot and highly-pressurized, especially in the vicinity of the initiator, where the generant has reacted. If these gases exit the inflator through the opening at such an elevated temperature and pressure, they can potentially damage the vehicle or injure vehicle occupants. Consequently, it is desirable to encase the initiator in some type of insert that effectively plugs the opening, while still permitting passage of the initiator through the opening.
However, it is difficult to form a reliable seal between the inflator and the insert, and still more difficult to effectively test whether or not the insert has effectively sealed the opening. Thus, the initiator is located inside a cavity that may or may not be open to ambient air. Such an arrangement, in which there is a low-pressure cavity within the initiator, can cause a number of problems, particularly with leak detection.
Typically, inflators are checked for leaks prior to installation in a vehicle. Leak detection may be accomplished by, first, filling the inflator with the appropriate mixture of gases. Often, a small percentage of trace material, consisting of an easily detected gas, is added. For example, helium is often added to inflators because helium occurs only in trace amounts in nature, and has a unique atomic weight that is easily detectable through mass spectrometry or other known methods. Radioactive isotopes may also be effectively used for trace materials. The inflator is then placed in a testing chamber, and the testing chamber is evacuated and then sealed. After a certain period of time, the amount of the trace material within the chamber is measured and recorded. If more than a trace amount of the gas is detected, the inflator is rejected and typically scrapped.
However, when there is a cavity within the inflator, that may or may not be sealed from the testing chamber, it is difficult to recognize whether detected leaks are from the main pressurized internal compartment of the inflator, which must remain sealed, or from the cavity, for which sealing from ambient air is not critical. More specifically, “virtual leaks” and “masked leaks” may be caused by such a cavity.
A “virtual leak” exists when gases remaining in the cavity during the evacuation of the testing chamber emerge after evacuation. Often the processes of assembling and filling the inflator leaves a certain amount of residual gas, including the trace material, within the cavity. Alternatively, these gases may be temporarily absorbed by the materials of the cavity, and may remain present until the cavity is subjected to the low pressure of the testing chamber.
Such a leak is a “virtual leak” because there is no real leak in the main internal compartment of the inflator, but the gas sensing equipment registers the presence of the gases from the cavity. Since it is difficult to detect exactly which part of the inflator is the source of gases detected in the testing chamber without comprehensive and time-consuming tests, it is often assumed that the inflator is defective if any significant amount of the trace material is present in the chamber after evacuation. As a result, virtual leaks result in the scrapping of many perfectly usable inflators. The lower yield of the inflator production process causes inflators, and airbag systems in general, to be more expensive, and therefore less widely available as lifesaving devices.
A “masked leak” occurs when there is an actual leak in the main internal compartment of the inflator, for example, in the pressure dome, but the leak is not detected. Gas leaks from the main internal compartment, which is at comparatively high pressure, into the cavity, which is at a lower pressure. However, the insert acts to keep the gases from escaping the cavity at a significant rate. Thus, after evacuation of the testing chamber, no significant amount of the trace material is registered.
Such a leak is potentially dangerous because a real leak exists in the inflator, and over the operating life of the inflator, which may be as much as 15 years, the compressed gas will leak out of the inflator. Without the compressed gas, it is likely that the airbag cushion will not inflate enough to effect occupants of the vehicle. It is also possible that the generant will become contaminated or moistened by exposure to ambient air. Thus, the generant may misfire, causing insufficient inflation of the cushion and potential danger to occupants of the vehicle. The leak is effectively “masked” because the insert does not permit the leaking gases to escape at a detectable rate. Even though the inflator is defective, it passes inspection and is installed in a vehicle.
Virtual leaks and masked leaks generally can be traced to the same root cause: the unpredictability of the seal provided by the insert. In the case of a virtual leak, the insert permits comparatively free flow of gases out of the cavity, and in the case of a masked leak, the insert seals off the cavity enough to prevent detection of the leak. Both problems are a result of the fact that the integrity (gastight sealing effectiveness) of the i
Neunzert Martin R.
Walker Kerry C.
Autoliv ASP Inc.
Brown Sally J.
Dickson Paul N.
Draper Deanna
Erickson James D.
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