U.S. Pat. No. 4,309,001 shows a seat belt retractor having a primary web receiving spool and an auxiliary shaft linked by gear. A rotating member travels on the auxiliary shaft to selectively control the position of a lock pawl. This retractor generally functions as an automatic locking retractor (ALR) and does not dissipate nor absorb energy as in the present invention. U.S. Pat. Nos. 3,952,967 and 3,927,846 show retractors having means for dissipating energy during a crash by deforming a part of the retractor.
It is an object of the present invention to provide a seat belt retractor that generates a generally constant, limited level, reaction force on the seat belt during an accident or emergency thereby limiting the loads that can be exerted on the seat belt by the occupant and in doing so providing a means of dissipating or absorbing crash energy. A further object of the present invention is to provide a retractor in which the above functions are generated remote from and communicated to the main spool of the retractor.
Accordingly, the invention comprises: a seat belt retractor comprising a spool for storing webbing thereon, the spool is rotationally mounted on a frame; a rewind spring is used to rewind or retract the webbing. The retractor includes at least one drive gear, having gear teeth, mounted for rotation with the spool and an auxiliary shaft rotationally mounted on the frame including a least one driven gear thereon in meshing engagement with the at least one drive gear. A ratchet nut is mounted to rotate with and slide along the auxiliary shaft. A first lock means prevents the rotation of the ratchet nut while permitting the nut to slide relative to the auxiliary shaft. A first energy absorbing means is mounted about the auxiliary shaft and is in selective contact with the ratchet nut for generating, when deformed by the ratchet nut, a relatively constant reaction force on the spool to oppose any protraction of the webbing during an emergency. An alternate embodiment of the invention includes a second ratchet nut, lock means and energy absorbing such as a bushing and means for activating the lock means in correspondence with certain accident parameters. In this manner the retractor can generate one of three different levels of reactive force on the seat belt.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.