Seat belt pretensioner device

Abstract

In a pretensioner device for automatically increasing a tension of a seat belt in case of a vehicle crash which uses a piston and cylinder arrangement as a power generator, a spring member resiliently urges the piston assembly in the direction of actuation so that any play that may be present in each connecting potion of the path of power transmission can be eliminated. Therefore, collision between component parts at the time of activating the power generator can be prevented, and the loss of energy which could arise from such collision can be avoided. The piston assembly may comprise a piston main body slidably received in the cylinder, and a piston rod having a base end abutting an opposing end of the piston main body and a free end projecting out of the open free end of the cylinder while the cylinder is provided with an inwardly directed radial flange for preventing the piston main body from being projected out of the cylinder. Thus, the piston rod may be kept removed from the assembly during transportation and storage so that an inadvertent activation of the power generator would only cause the movement of the piston main body inside the cylinder, and the handling of the assembly can be therefore simplified.