Land vehicles – Wheeled – Attachment
Reexamination Certificate
1999-02-23
2002-11-05
Culbreth, Eric (Department: 3616)
Land vehicles
Wheeled
Attachment
C280S736000, C280S742000
Reexamination Certificate
active
06474684
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a gas-generating device or inflator suitable for rapidly inflating a flexible bag or filling a container to an elevated pressure. More specifically, this invention relates to a gas-generating device capable of modulated pressurization.
BACKGROUND OF THE INVENTION
Rapid gas-generating devices or inflators, as they are referred to in the art, have found widespread use. One use is in passive air bag restraint systems in order to reduce the large number of deaths and injuries occurring in automobile accidents annually. Air bags and inflatable belts for passive restraint systems are operatively associated with inflator devices which are generally activated by an inertial switch or sensor which detects rapid deceleration of a vehicle such as that which occurs upon impact between an automobile and another object. When the inertial switch is triggered, it causes an inflator to inflate a collapsed flexible bag or belt quickly which is deployed into a protective position in front of the occupant. The bag or belt must inflate extremely rapidly after the primary impact or collision in order to protect the occupants from injury caused by secondary impact or collision with the interior of the vehicle. In order to meet such criteria, the bag or belt should be fully inflated within about 10-65 milliseconds after inflation has been initiated.
A variety of conflicting considerations must be taken into account in developing an effective air bag passive restraint system. First, the inflator must be capable of producing and/or releasing a sufficient quantity of gas to the air bag within the time limitation required of a passive restraint air bag system, given the time limitation involved in air bag restraint systems, roughly about 10 to 15 milliseconds for side impact applications and about 30 to 65 milliseconds for driver and front passenger applications. Inflators must be capable of filling an air bag in these time frames with 15 to 50 liters of gas for side applications and 60 to 200 liters of gas for driver and front passenger applications. The specific amount and rate of gas generation or release is determined by the required air bag volume and the vehicle structural rigidity which influences the time between primary and secondary impacts.
Other considerations in designing an inflator for a passive air bag restraint system, particularly for automotive applications, include the toxicity and noxiousness of the gas which fills the air bag. That is, for air bags that deflate by releasing gas into the confines of the interior of the vehicle and in the case where the airbag ruptures, the inflator for an automotive air bag must generate or release gas and other materials which meet or surpass certain non-toxicity requirements in order to protect the occupants. Otherwise, toxic or noxious gas may injure or cause illness to the occupants. For example, the release of too much carbon monoxide could cause illness and even be deadly to the occupants. These toxicity requirements are controlled by certain specifications required by the automotive manufacturers. For example, a typical automotive requirement is that an inflatable air bag system meet certain specifications for a 100 cubic foot compartment. These toxicity specifications are set by health requirements and one reference which is helpful in defining those requirements is OSHA workplace breathing air standards, another reference is the American Conference of Governmental Hygienists' Allowable Limits for Short Term Exposure Levels for the Workplace.
In addition, the gas-generating composition may be highly toxic or unstable requiring special handling during the manufacturing process and creating disposal problems at the end of the useful life of the vehicle. For example, raw sodium azide which is used as the gas-generating composition in most airbag inflators today has a relatively high toxicity which creates handling problems during the manufacturing process.
Other considerations include that the gas and any other materials, for example solid particles, released into the air bag must meet energy transfer restrictions so that it will not burn or deteriorate the integrity of the air bag. Insuring that the energy and materials transferred during the inflation event do not burn, puncture or deteriorate the bag, protects the occupants from injury and insures proper bag inflation.
Packaging restrictions add a further consideration in the development of passive air bag inflators. For example, weight and size are primary factors in determining the suitability of vehicle inflator embodiments. Weight reduction translates into fuel economy improvements and size reduction into styling and design flexibility. For styling reasons and customer-acceptance, and so as not to interfere with the occupants' movement, comfort or the driver's line of vision, it is desirable to arrange the inflator so as not to be obtrusive, and yet have it positioned so that it effectively accomplishes its intended task. In order to accomplish these styling, customer-acceptance and engineering design parameters, the inflator must be capable of being packaged in a compact manner. For example, it is desirable to package the inflator in an air bag module which fits with the hub of the steering wheel while still allowing the use of the vehicle's horn by depressing any part of the steering wheel hub and while additionally allowing the use of the numerous control switches and stalks on the steering column. It is further advantageous for side impact bags to package the inflator and air bag module between the exterior door panel and the trim or panel in the interior of the door.
The emphasis on weight reduction for the purpose of fuel conservation in motorized vehicles, and the recent development of passenger air bags, rear-seat occupant air bags, side-impact air bags, seat-belt air bags and knee-bolster air bags as well as the contemplated use and development of air bags in the A and B pillars of vehicles and other small bags of 1 to 30 liters of volume, have created the need and demand for a light and compact inflation system.
There are basically two methods or systems which are employed to supply the gas in air bag restraint systems. In one method, the inflating gas is provided as a compressed gas stored onboard the vehicle within a pressure vessel. In the second method, the bag is inflated by igniting a pyrotechnic gas-generating propellant composition and directing the resultant gaseous combustion products into the bag. These two methods create three categories of inflators, the first relies solely upon a pressurized reservoir of gas, the second upon burning a combustible propellant to generate all of the gas to fill the air bag, the third upon a combination of the two described methods to inflate the air bag, and is known in the art as a hybrid inflator.
The first method requires a reservoir of gas stored onboard the vehicle at a very high pressure which is discharged into the bag immediately upon sensing the impact. In order to inflate the vehicle occupant restraint bag in the required time of 0.010 to 0.065 seconds, that is to attain a fill volume rate of at least about 900 liters per second and preferably approximately 3,000 liters per second, a relatively large reservoir of gas at pressures of 3,000 pounds per square inch (“psi”) is stored in a pressure vessel. To open the pressure vessel in the short time interval required to inflate the air bag, explosive actuated arrangements are employed for bursting a diaphragm or cutting through a structural portion of the reservoir.
In the second method, a pyrotechnic gas generator having an ignitable and rapid-burning gas-generating propellant composition burns to produce substantial volumes of hot gaseous products which are directed into the inflatable bag. These gas generators must withstand thermal and mechanical stresses during the gas-generating process. Specifically, the gas-generating propellant ignites, combusts and burns at elevated temperatures and pressures which re
Bednarz John
Hansen Glade L.
Ludwig Christopher P.
Muir Martin J.
Scaven Gregory J.
Culbreth Eric
Fitzpatrick ,Cella, Harper & Scinto
Talley Defense Systems, Inc.
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