US Patent 7325280 Tongue and seat belt apparatus employing the same

During ordinary use (i.e., a non-collision state) a webbing guide and a locking bar are biased in the counter-clockwise direction by the biasing force of the bar spring and are held in their initial positions so that spaces are set. Since a webbing passes through the spaces, a tongue can smoothly slide relative to the webbing. During a vehicle collision, a pulling force exceeding a predetermined value is applied to the webbing in the direction of an occupant's lap and shoulder. By this pulling force, the webbing guide rotates in the clockwise direction and the locking bar rotates in the counter-clockwise direction and linearly moves rightward. Therefore, the webbing is clamped between the locking bar and the tongue body. The clamping force at this point includes a force pulling the webbing and the biasing force of a bar spring so that a large clamping force can be obtained.