Abstract
Air bags have proven to be an effective device of reducing injury risk in impacts. But in particular situations, in which the occupant is seated unusually close to the air bag module (so-called OOP: out of position) and comes in contact with the air bag during its deployment, the air bag can rather endanger than protect the occupant.
The folded air bag is an important component of the air bag module. Tests have also indicated that the fold scheme has a significant influence on occupant injury.
In this paper the air bag fold scheme is of special interest. Three fold schemes of air bags in todays and future market, so-called leporello-(conventional) folding, raff-folding (also called Petri-folding) and z-folding (air bag with integrated crash-cushion), are introduced. Their potential to reduce air bag aggressiveness is evaluated and compared with each other.
Finite Element Technique is widely used in numerical simulation for occupant safety. However, modelling folded air bags and exactly simulating air bag shapes during deployment is a very complex problem. Especially for raff- and z-folding with crumpling, distortion or crushing, generating folded meshes of air bags is very difficult. Therefore a pre-processing was developed to generate the nods and elements of folded air bags and was combined with MADYMO program during the simulation. The unfolding process of folded air bags was effectively simulated.
The solution procedure is systematically divided into three steps: 1) development of a pre-processing in order to model folded air bags and generate meshes, 2) simulating static unfolding process to show which influence the fold schemes have on the physical parameters (e.g. pressure , volume, etc.) and 3) simulating collision process to investigate the interaction between air bag and dummy and evaluating the protection of these fold schemes.
The results of this work show that the air bag scheme strongly influences its aggressiveness. Raff-folding and z-folding should offer more effective protection for car occupants being out of position. But with the occupant in the normal position these three fold schemes do not show significant differences. Because of the location of air bag upper and lower layer the fold layers of raff- and z-folding do not interfere with each other during deployment. Unfolding of both these fold schemes takes place more gently. The variation in the shape of the air bag module and the number of air bag folds with raff-folding and z-folding has no significant influence on the static unfolding process.