Seat belt retractor with an electric motor

Abstract

A seat belt retractor includes a spool driven by an electric motor. Seat belt webbing is wound around the spool. A worm wheel rotates with the spool and meshes with a worm that is axially movable. A set of electrical brushes is axially movable with the worm along the shaft. The set of electrical brushes is electrically coupled to a control circuit through a set of conductor strips. The set of brushes slide along the set of conductor strips as the worm moves axially. In response to movement of the brushes along the conductor strips, the control circuit provides signals to control the motor and, thus, the spool. When an occupant initially withdraws the webbing to buckle the webbing, the tension force acting on the webbing moves the worm axially. In response, the motor is actuated to rotate the spool in the belt withdrawal direction and provide motorized assist for the webbing withdrawal. After the tension force acting on the webbing decreases below a predetermined amount and a predetermined time elapses, the motor rotates the spool in the belt retraction direction and tightens the webbing against the occupant. After the webbing tightens against the occupant with a predetermined amount of force, the motor rotates the spool in the belt withdrawal direction until a small amount of slack in the webbing is established. While the webbing is buckled, if the occupant moves so as to form excess slack in the webbing, then this sequence of retracting the webbing against the occupant and paying out the small amount of webbing is repeated. If a crash occurs while the webbing is buckled, then the meshing engagement of the worm wheel with the worm prevents the worm wheel and the spool from rotating and locks the retractor.