Pretensioner

Abstract: A pretensioner for a vehicle safety restraint arrangement, the pretensioner comprising a piston mounted in a guide chamber for translational movement tangentially to a spool shaft, so that in travelling through the guide chamber, the piston engages the periphery of the spool shaft and causes it to rotate, and wherein the region of the chamber into which the piston moves after engaging the shaft has a wall which is weakened so as to be deformable to absorb force from the movement of the piston towards the end of a piston stroke.

Description: The present invention relates to a pretensioner for a vehicle occupant safety restraint and particularly to a buckle pretensioner. Pretensioners are used to rapidly pull in any slack in a safety restraint seat belt at the onset of a crash condition so as to more securely restrain the occupant against forward movement and potential injury by collision with internal features of the vehicle. In addition, the pretensioning operation aims to pull the occupant into, or at least towards, the correct seating position so as to maximise the effect of a second restraint such as an airbag. A pretensioner according to the preamble of claim 1 is known from EP 0 629 531 A. A modern seat belt is known as a 3-point restraint because it is secured to the vehicle at three points arranged about the occupant so as to provide a diagonal torso section and a horizontal lap portion to hold the occupant in the seat. The belt is attached to the vehicle by a spring loaded retractor tending to pull in the belt, and by a buckle for quick release of the belt. Pretensioners can be sited at the retractor or at the buckle end of the restraining seat belt. The present invention aims to provide an improved, and more compact pretensioner, than hitherto known. According to a the present invention there is provided a pretensioner for a vehicle safety restraint arrangement, the pretensioner comprising a piston mounted in a guide chamber for translational movement tangentially to a spool shaft, so that in travelling through the guide chamber, the piston engages the periphery of the spool shaft and causes it to rotate, and wherein the region of the chamber into which the piston moves after engaging the shaft has a wall which is weakened so as to be deformable to absorb force from the movement of the piston towards the end of a piston stroke. The pretensioner may be used directly with a vehicle safety restraint retractor in which case the spool is the spool of the retractor itself and provides for a compact and efficient retractor pretensioner. However, it can also be used with a safety restraint buckle if the spool is wound with a cable which is arranged to transfer force to the safety belt or the buckle mounting. The guide chamber for the piston may comprise a cylinder (which may have a rounded or rectangular cross section, depending upon the corresponding cross-section of the piston), optionally in combination with a load bearing cradle supporting the spool shaft. Either the wall of the cylinder or the wall of the cradle may be used for absorbing the kinetic energy of the piston. For example, the cylinder may be closed and its side walls at one end weakened so as to be deformable. Alternatively the cylinder may be mounted in a load bearing cradle which also supports the spool shaft. The walls of the end of the cradle are weakened, for example by means of cut-outs, and the kinetic energy of the piston absorbed in this way by the cradle as the cut-outs allow the wall effectively to stretch. For a better understanding of the present invention and to show the same may be carried into effect, reference will now be made by way of example to the accompanying drawings in which: Figure 1 is a perspective view of a pretensioner according to one embodiment of the invention, in an inactivated state; Figure 2 shows the pretensioner of figure 1 in an activated state; Figure 3 is a cross sectional view of the pretensioner of figure 1. A single piston 111 is arranged on one side of a rotatably mounted spool shaft 108. The piston 111 is mounted to be slidably movable along the inside of a cylinder 109 and so as to contact the spool shaft in the mid part of its stroke. It is driven by a gas generator (now shown) and teeth 117 on the piston 111 engage teeth 118 on the spool shaft 108 and cause the spool shaft to turn. The cylinder 109 is supported in a load bearing cradle 130, which may for example be made of steel, and which also supports the spool shaft 108 for rotation. The lower parts of the side walls of the cradle 130 are weakened with cutout portions 132. At its lower end the cylinder 111 is open and the moving piston therefore exits the cylinder after it has moved past and turned the spool shaft. It then impacts the end wall 131 of the cradle 130, as shown in Figure 5, and the force of impact stretches the sides of the cradle in the regions of cut-outs 132. Alternatively the end of the cylinder may be closed with a weak end wall which fractures relatively easily but which also absorbs some of the force of the piston 111. The cut-outs 132 may take a variety of shapes. Those illustrated are generally triangular and diamond shaped, so as to leave a diagonal lattice structure of metal in that region of the cradle. The force of the piston 111 pulls the diagonals into more vertical lines as the piston slows. Other shapes will be evident to a person skilled in the art: for example horizontal line cut-outs would also effect the requisite weakening of the walls of the cradle. It is however desirable to avoid the wall shearing or fracturing altogether since this would allow the piston to escape from the safety arrangement releasing a projectile into the vehicle occupant seating area!

Claims: A pretensioner for a vehicle safety restraint arrangement, the pretensioner comprising a piston mounted in a guide chamber for translational movement tangentially to a spool shaft, so that in travelling through the guide chamber, the piston engages the periphery of the spool shaft and causes it to rotate, and characterised in that the region of the chamber into which the piston moves after engaging the shaft has a wall which is weakened so as to be deformable to absorb force from the movement of the piston towards the end of a piston stroke. A pretensioner according to claim 1 wherein the spool is the spool of the retractor. A pretensioner according to claim 1 when used with a safety restraint buckle comprising a cable wound on the spool and arranged to transfer force to safety belt webbing or to the buckle mounting. A pretensioner according to any one of the preceding claims comprising a cradle supporting the spool shaft pinion, and being connected in load bearing manner to the frame of the retractor. A pretensioner according to claim 4 wherein the cradle is formed of steel. A pretensioner according to claim 4 or 5 wherein the cradle comprises means for absorbing forces. A pretensioner according to claim 6 comprising a weakened section in at least one wall of the cradle to absorb some of the energy of the moving piston. A pretensioner according to claim 7 wherein the weakened section comprises cut-outs. A pretensioner according to any one of the preceding claims wherein the cylinder is closed and at least one side wall at one end is weakened as to be deformable. A pretensioner according to any one of the preceding claims wherein the cylinder and piston have substantially circular cross-sections. A pretensioner according to any one of the preceding claims wherein the cylinder and piston have rectangular cross-sections.

Inventors: AROLD JURGEN, JAIN TONY, JAMES FOSTER HOWARD, AROLD, JURGEN, JAIN, TONY, JAMES FOSTER, HOWARD
Applicants: KEY SAFETY SYSTEMS INC, KEY SAFETY SYSTEMS, INC.
Application year: 1999
Main classification: B60R22
IPC codes: B60R22