Patent ID: 8006927
Filing Date: 2011-08-30
Classification: B60R

Abstract:
1. A force limiting device for use with a safety belt retractor, the safety belt retractor including a spool, a safety belt webbing attached to and wound around the spool, the spool being rotatable to wind in the webbing and to payout the webbing under the influence of forwardly directed movement of a vehicle occupant, the force limiting device comprising: a fixed member; a shaft connected to the fixed member, at least a portion of the shaft is threaded; and a coupling received on the shaft and having an internal thread for threadedly engaging the threaded portion of the shaft, the coupling being configured to move along a longitudinal extent of the shaft, the coupling being operatively connected to the spool and moving towards the fixed member during payout of the webbing, engagement of the coupling with the fixed member preventing further payout of the webbing, wherein the threaded portion of the shaft includes a first threaded section having a first thread pitch and a second threaded section having a second thread pitch, each of the first thread pitch and the second thread pitch differs from a thread pitch of the coupling to limit movement of the coupling along the longitudinal extent of the shaft during payout of the webbing by increasing the force required to turn the coupling on the threaded portion of the shaft, the first threaded section providing a generally constant belt force on the vehicle occupant, the second threaded section providing an increasing belt force on the vehicle occupant.