1997-02-24

Chest Injury Risks to Drivers for Alternative Air Bag Inflation Rates 970129

While the present air bag systems have been shown to be highly effective in high severity crashes, undesirable side effects have been reported in some low severity events. The inflation rate of the airbag during deployment has been cited as a factor which induces injuries. A rapid airbag deployment rate is advantageous to provide protection to occupants in severe crashes. On the other hand, airbag aggressivity associated with the high inflation rate can increase injuries in the lower severity crashes. The injury producing forces from the airbag increase as the occupant position becomes closer to the bag at the time of deployment.
This paper describes the results of an analytical study to evaluate chest injury measures for reduced inflation rates of a Taurus type air bag in a variety of crash modes. A detailed nonlinear finite element model of an unfolding airbag and a 50th percentile male Hybrid III dummy are used in conjunction with a test buck to simulate frontal crashes. The model is calibrated for a 30 mph crash, and then used to evaluate the effects of chest loading for other crash modes and air bag flow rates. Different acceleration time histories are introduced to model high speed (35 mph) crashes and low speed (16 mph) pole impacts. A series of parametric simulations are performed for the unbelted dummy by varying the deployment time and the gas flow rate.
A barrier crash at 20 mph was simulated with three variations in flow rate, and occupant position at inflation. The results suggest that a flow rate greater than 60% is desirable to prevent steering wheel contact by the dummy.
Simulations of different crashes indicated that a 75% flow rate reduced chest injury measures in the 35 mph offset crash, and at all cases simulated at severities of 3d mph and below. The 75% flow rate increased chest injury measures in the 35 mph barrier crash.
The simulation of a 16 mph pole crash with late deployment indicated that chest injury readings for this case were higher than in the 35 mph barrier crash. The 75% flow rate reduced chest injury measures in this case by 25%.
Reducing the air bag flow rate to about 75% significantly reduced the chest injury risk to a normally seated, unbelted, 50th percentile male dummy in moderate and low severity crashes. A reduction in the margin of distance between the chest and steering wheel also resulted. However, the 75% flow rate prevented contact with the steering wheel in all cases simulated.

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