The effectiveness of occupant restraint system is generally reduced as the impact velocity of vehicle increases. The addition of a pre-loading device to seat belt system has been proposed as one of useful measures to this kind of degradations.

This paper proposes the optimum selection of activation time and level of load produced by the assumed preloading device in case of 2-point diagonal seat belt system with knee bolster on the frontal impact at 40mph.

The two dimensional, five mass occupant mathematical model is developed and the validation of the model is carried out by adjusting various parameters of the model in comparison of the simulated results with those of the actual sled test, where a typical pre-loading device is employed.

The set of optimum parameters of pre-loading device is derived in relation to the level of HIC (head injury criteria) and the displacement of occupant through the computer simulation of this kinematic model.