Emergency locking retractor for a seat belt assembly

An emergency locking retractor for a seat belt assembly wherein a reel for paying off and winding up webbing is fixedly mounted on a reel shaft which is rotatably mounted to a frame and which is spring energized in a direction to cause retraction of the webbing, the retractor comprising:

• (a) a locking mechanism for locking the reel against rotation comprising:
• (1) a cogwheel fixedly mounted on an extension of the reel shaft;
• (2) a locking ring concentrically surrounding the reel shaft extension and having cam follower means for axial movement toward and away from the cogwheel, the locking ring being adapted to lock the cogwheel, and therefore the reel, against rotation relative to the frame when moved toward the cogwheel;
• and
• (3) first resilient means connected between the cogwheel and the locking ring to impart the rotation of the former to the latter, the first resilient means yieldably urging the locking ring away from the cogwheel;
• (b) a webbing sensor mechanism for causing the locking mechanism to lock the reel against rotation in response to the extension of the webbing at a rate in excess of a predetermined limit, the webbing sensor mechanism comprising:
• (1) a cam disc rotatably mounted on the reel shaft extension and normally engaged with the cam follower means of the locking ring for joint rotation therewith, the cam disc being effective, when locked against rotation relative to the frame in a direction of webbing extension, to cause the locking ring to move toward the cogwheel against the bias of the first resilient means and hence to cause the locking ring to arrest the rotation of the reel;
• (2) a curved sensor arm medially pivoted in an eccentric position on an outer face of the cam disc for movement between a retracted and a working position, the sensor arm being adapted to pivot from the retracted to the working position upon exertion of a force on its first end tending to arrest the revolution of the sensor arm with the cam disc in the direction of webbing extension;
• (3) a pawl at a second end of the sensor arm which projects beyond the circumference of the cam disc upon pivotal movement of the sensor arm to the working position;
• (4) second resilient means biasing the sensor arm from the working toward the retracted position;
• (5) an annular member mounted in fixed relation to the frame and concentrically surrounding the reel shaft extension, the annular member having a set of internal ratchet teeth to be engaged by the pawl of the sensor arm upon pivotal movement thereof to the working position against the bias of the second resilient means, the cam disc being locked against the rotation in the direction of webbing extension upon engagement of the pawl with one of the internal ratchet teeth;
• and
• (6) an inertia member rotatably mounted on the reel shaft extension and operatively engaged with at least the first end of the sensor arm so as to be free to rotate relative to the sensor arm and the cam disc within limits, the inertia member having a greater mass than the combined mass of the cam disc and the sensor arm whereby upon rapid rotation of the reel due to the extension of the webbing at a rate in excess of the predetermined limit, the inertia member lags behind the cam disc thereby relatively acting on the first end of the sensor arm to cause same to pivot from the retracted to the working position against the bias of the second resilient means;
• and
• (c) a lockup prevention mechanism for maintaining the sensor arm in the retracted position during, and at the end of, the retraction of the webbing by the force of the spring in order to make possible the smooth re-extension of the webbing.