Development of a Brake-Operated Pre-Crash Seatbelt System and Performance Evaluation

The brake-operated pre-crash seatbelt system retracts the seatbelt webbing by activating an electric motor attached to the seatbelt retractor. Detection of emergency braking is used as a trigger to activate the motor. Retracting the seatbelt helps to reduce an occupant's forward movement due to inertial force acting on the occupant's body during deceleration in braking. Addtionally, retraction of the seatbelt webbing also helps existing occupant restraint devices to work more effectively in a crash.

The effectiveness of the pre-crash system was evaluated by considering two conditions combined. One involved the dynamic behavior of the vehicle and occupants prior to a crash. The other concerned the safety performance of the vehicle during the crash event. Experiments were conducted to measure the behavior of the vehicle and occupants under emergency braking prior to a crash. The experimental results were then used in numerical simulations as the initial conditions for calculating parameters related to vehicle safety during a crash event. The results showed that the brake-operated pre-crash seatbelt system has the potential to reduce injury parameters even if emergency braking is applied prior to a crash.

This paper will describe how the experimental results and numerical simulations were combined to evaluate the effectiveness of the pre-crash system. The effectiveness of reducing an occupant's forward movement during emergency braking will be shown on the basis of experimental results. The effects of an occupant's forward movement on injury parameters during a crash event will be described in relation to the numerical simulation results.