In a vehicle occupant protection system comprising a seat for seating a vehicle occupant in a passenger compartment of a vehicle, and a seat belt for restraining a vehicle occupant seated in the seat, the seat belt is pulled rearward by a power actuator in an early stage of a vehicle crash to apply deceleration to the vehicle occupant before the vehicle body has started decelerating so that the vehicle occupant is prevented from being subjected to a deceleration level which is higher than an unacceptable level of deceleration throughout the entire period of the vehicle crash.
An end of a seat belt is connected to an actuator that can selectively remove a slack from the seat belt. The actuator includes a main actuator unit, a flywheel which provides a maximum inertia effect for a given space, and a cushioning member for decelerating a movement of the moveable end of the seat belt following a certain initial travel of the moveable end. The main actuator unit produces an early rise in the vehicle occupant deceleration, and the cushioning member smoothly connects the time history of the vehicle occupant deceleration to a ride-down condition whereby the deceleration acting on the vehicle occupant is favorably spread over time, and the maximum level of the deceleration can be minimized. The flywheel contributes to a favorable shaping of the time history of the vehicle occupant deceleration.
