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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.

This paper describes a low-cost servo acceleration sensor suitable for automotive applications such as the antilock braking system or the traction control system. The sensor comprises a weight, a pair of flat springs, a magnetic circuit, an optical system and an electric circuit. The weight consists of a torquer coil and a pair of damper plates. In order to reduce the cost, we developed a unique construction suitable for mass production. The results of the performance tests show an excellent linearity and fine temperature characteristics over the operating temperature range of -40 to +85° C.