Seat belt retraction apparatus including an inertia sensor

Abstract

Seat belt retraction apparatus including a seat belt retractor mechanism, an inertia sensor and an electrical circuit interconnected with the inertia sensor and the retractor mechanism. The retractor mechanism includes a reel and a reel locking mechanism for locking the reel against unwinding of the strap of the seat belt wound around the reel. The illustrated reel locking mechanism includes a pawl which is engageable with ratchet wheels on the reel to prevent the reel from paying out the strap. This pawl is movable between a first position in which the pawl is out of locking engagement with the ratchet wheels and a second position in which the pawl engages the wheels to lock the reel against extension of the strap. An electromagnetic device including a coil is provided for controlling movement of the pawl. The inertia sensor is carried on the vehicle chassis and has a piezoelectric disc. The sensor also includes an inertia weight such as a pendulum for changing the shape of the disc so that the sensor provides an output signal in response to a change in velocity of the vehicle. The electrical circuit is responsive to the operation of the inertia sensor to energize the coil.