Land vehicles – Wheeled – Attachment
Reexamination Certificate
2000-04-19
2001-08-14
Culbreth, Eric (Department: 3611)
Land vehicles
Wheeled
Attachment
C137S512100, C137S857000
Reexamination Certificate
active
06273463
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to devices or systems for improving the performance of airbags, and specifically to pressure-control devices that retain and release the inflation gases in a controlled manner and are further capable of quickly venting the gases when necessary.
BACKGROUND OF THE INVENTION
The first airbag systems for automobiles were developed in the 1970's. Since then, airbag systems have saved lives and prevented or reduced serious injury in numerous automobile crashes. Statistically, the effectiveness of airbag systems is without question. The success of airbag systems has also prompted their use in areas other than automobiles. In recent years, airbag systems have been developed for helicopters and general aviation aircraft. Airbags are also being used in various recovery systems, as energy absorbing devices, to reduce the landing impact of aircraft escape capsules, rockets or other space vehicles, and to reduce the landing impact of military cargo drops. Despite several years of development, improvement, and widespread use of airbag systems, problems still remain.
Where airbags are used for vehicle recovery or for cargo drops, problems are primarily related to poor efficiency, and therefore to excessive bag height which can result in payload rollover. In such uses, airbag performance requirements are generally described by the maximum impact force permitted (deceleration) and the mass and velocity of the payload at touchdown. Maximum efficiency is achieved when the system operates at a constant deceleration force slightly less than the maximum permissible deceleration force. This results in the minimum possible distance over which the kinetic energy of the payload can be absorbed.
When airbags are used for vehicle occupant protection, system efficiency is also very important. Of greater concern however, are system performance, reliability and safety considerations. Although a statistically small number, there have been some incidents where the airbag caused severe injury or even death. Many of these incidents have occurred in what is commonly called an out of position situation (OOPS). Simply stated, the occupant is too close to the airbag when the airbag deploys.
Some of the airbag induced injuries are due to crash sensor systems which do not adequately discriminate between crashes and minor impacts.
Some injuries are due to the very aggressive airbag developed in the United States because of requirements for protecting occupants not wearing lap and shoulder belts. The less aggressive airbags developed in Europe, where unbelted occupants are not a design concern, inflict fewer injuries. However, even with perfect sensors and less aggressive airbags, some out of position occupants would still be injured.
Some other airbag induced injuries relate to the wide variation in occupant size and weight. Conventional airbag systems are designed to produce a fixed set of performance parameters, e.g. inflation time, initial pressure, and venting. This set of parameters is intended to protect the widest possible range of occupant sizes. Unfortunately, the system may not provide adequate protection for a very large occupant and conversely, may be injurious to a very small individual.
These cases of airbag injury have attracted considerable media attention, especially when children are involved. This negative publicity has somewhat overshadowed the benefits of airbags, and has caused a fear of airbags among some vehicle owners. Some are even opting to have a lockout switch installed so the airbag system can be completely turned off. Doing so will indeed prevent airbag induced injuries but, unfortunately, the vehicle occupants are also forfeiting any possible benefits of the airbag system.
A unique problem also exists in the present U.S. Army cockpit airbag system (CABS) for Blackhawk, Seahawk, and Kiowa helicopters. These airbag systems are not vented like auto airbag systems are vented. The reason is that the typical crash scenario is much more protracted (e.g. tree strikes prior to ground impact or effects of very rough terrain) so a longer period of bag inflation is required. Therefore, the design and production of the inflator must be very precise to achieve the proper initial pressure. This is particularly difficult to achieve under the temperature extremes in which these helicopters operate. In very cold temperatures, the inflator must provide a certain minimum bag pressure for crew member protection. Unfortunately, in some instances, similar inflators may cause bag ruptures during high temperature use.
Another problem with conventional airbag systems is their size and bulk. This is particularly true of passenger airbag modules. Typical airbags must be larger than their ideal size because of their relatively inefficient fixed vent design. The “oversize” bags then require bulky modules for stowage and increase chances for airbag induce injury.
An ideal airbag system would inflate to a pre-determined pressure, provide an acceptable level of deceleration for the occupant, and maintain that deceleration at a nearly constant value during a crash event. The system would be adjustable to provide the proper deceleration for various size occupants. It would also have the ability to prevent serious injury to any occupant, by venting a large amount of propellant gases very early in the inflation cycle if the occupant is too close to the airbag. In contrast, a typical automotive airbag module only has nonadjustable vents in the airbag fabric. This conventional approach of “one size fits all”, presents obvious compromises relative to occupant size and crash situation. Also, having vents in the airbag fabric requires that the airbag must unfold before any gas flow can reach the vents. In a very close OOPS, all of the inflation gases are confined in the airbag module creating a very high pressure, and therefore, a potentially hazardous force on the occupant.
The high media publicity focused on these problems (especially those in the public domain) has prompted numerous proposed solutions. Many of these proposed solutions address a “depowered” airbag, which will deploy with less velocity. This approach can reduce the incidence and severity of airbag induced injuries in minor crashes, but may also compromise the performance of the airbag system in severe crashes.
In proper system operation, the airbag inflates before the occupant enters the area that will be occupied by the airbag. A design rule of thumb, that has appeared in the literature over the years, is that the airbag must be fully deployed before the occupant has moved forward (due to crash acceleration) more than 5 inches from the normal sitting position. Some crash sensors perform this calculation and do not fire the inflator if the criterion is not met. While this prevents possible airbag induced injury, it follows that any benefit that might have been provided by the airbag has also been defeated.
Other proposals include a great variety of sensors intended to detect the size and position of seat occupants (especially the passenger) and microprocessor circuitry programmed with appropriate logic to control airbag deployment. Depending on the specific crash situation, these “smart airbag systems” may deploy using the full power of dual inflators, deploy with less force by using only one inflator, or not deploy at all. Again, if the system does not deploy, any possible benefit during a crash event has been forfeited.
Considerable research on improving the efficiency of cargo drop airbag systems has been conducted or sponsored by U.S. Army Soldier Systems Command, Natick, Mass. Numerous studies have been conducted with airbags having fixed exhaust vents. Studies have been conducted with various auxiliary devices. One such system involved injecting compressed air into an airbag while the airbag was being compressed. Another system, described in ASME Paper No. 091-WA-DE-1, uses a servo-controlled, mechanical sliding vent closure to affect greater system efficiency. A recent research program conducted
Peterson Leslie D.
Zimmermann Richard E.
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