Seat belt pretensioner

#The present invention relates to a seat belt pretensioner.

#A typical seat belt comprises a length of belt webbing connected at three points to load bearing parts of a vehicle. Typically one end of the webbing is attached to a belt anchor that is bolted to a load bearing longitudinally extending chassis member on one side of a seat between the seat and the adjacent door. The webbing is arranged to pass laterally across the hips of a seat occupant to a buckle mechanism fixed to the vehicle on the opposite side of the seat, and then diagonally across the torso of the seat occupant, via a webbing guide, to a retractor mounted on the B pillar adjacent the door. A buckle mechanism engages a buckle tongue that is attached to the webbing in a sliding manner.

#The retractor fitted at the pillar end of the webbing increases the comfort of the seat occupant restrained by the belt by allowing the webbing to pay out under relatively low loads to enable limited. This allows movement of the restrained seat occupant, for example to reach in-car entertainment controls or storage compartments. The retractor is biased to keep the webbing relatively taut about the seat occupant and a locking element is included to lock the retractor against webbing payout if an acceleration sensor senses the vehicle undergoing rapid acceleration or deceleration indicative of a crash.

#FIG. 1 is a schematic side view of a pretensioning apparatus according to a first embodiment of the present invention, in an unworn configuration wherein the seat belt is not restraining a seat occupant.

#FIG. 2 shows the pretensioning apparatus of FIG. 1 in a worn configuration wherein the seat belt is restraining a seat occupant.

#FIG. 3 shows the pretensioning apparatus of FIGS. 1 and 2 in a pretensioned configuration wherein the seat belt is restraining a seat occupant.

#As used throughout this description, and in the claims, terms such as “forward” and “rearward”, “front” and “back” and similar terms are understood to refer to directions with respect to the front and rear of a vehicle in which the seat belt pretensioning apparatus of the invention is installed. Similarly, terms such as “above” and “below”, and “higher” and “lower” are understood to be relative to the normal orientation of the top and bottom of a passenger compartment of a vehicle in which the seat belt pretensioning apparatus of the invention is installed.

#In all the figures a vehicle seat 1 is shown fitted with a seat belt in known manner. The seat belt comprises seat belt webbing 2, one end of which is attached to, or connected in a load bearing manner 3, to a load bearing part of the vehicle. It may be anchored to a chassis member, part of the floor of the vehicle, to a doorsill or to part of the seat 1 or the seat rail to which the seat frame is slideably attached. Preferably a tubular member, such as a cylinder 7 is anchored to a load bearing part of the seat such as the seat rail or generally parallel to it. As used herein and in the claims the word “tubular” is understood to have its common meaning of a conduit comprising a long hollow object used to hold and conduct objects, and that while a tube is usually cylindrical it may have any other appropriate cross section shape including square or rectangular. The webbing 2 passes via a webbing guide 5, such as a D-ring, to a retractor 4, typically fixed to the B pillar of a vehicle. A pretensioning unit is shown at 6 and this would typically comprise, as is well known, a piston-cylinder unit in which a piston 13 is driven along a tubular member, here a cylinder 7, usually by pyrotechnic means, in the event of a crash. The piston 13 is connected by a cable 9 to the webbing 2. A pulley 15 is located forward of the cylinder 7 to redirect the cable 9 from extending in a forward direction to a rearward direction towards the seat belt webbing 2. Here the cable 9 is shown looped around the belt webbing 2.

#Seat belt pretensioners having a piston driven in a tubular member, such as a cylinder, to tighten a seat belt are disclosed, for example, in: U.S. Pat. No. 6,113,145 A; U.S. Pat. No. 6,131,951 A; U.S. Pat. No. 6,149,095 A; U.S. Pat. No. 6,155,512 A; U.S. Pat. No. 6,186,549 B1; U.S. Pat. No. 6,237,958 B1; U.S. Pat. No. 6,238,003 B1; U.S. Pat. No. 6,450,435 B2; U.S. Pat. No. 6,565,121 B2; U.S. Pat. No. 6,840,544 B2; and U.S. Pat. No. 6,682,097 B2, each of which is incorporated herein by reference to teach such a piston-tubular member/piston-cylinder device which alone or in combination with one or more of the other cited publications teaches a piston-tubular member/piston-cylinder device that may be used in the practice of the present invention.