High seal retractor pretensioner piston

A pretensioner assembly for retracting a seatbelt webbing of a motor vehicle, the pretensioner assembly comprising:

• a bent tube;
• a gas generator for producing gas conducted within the tube;
• and
• a piston disposed within the tube and operable to drive a driving element upon receiving pressurized gas discharged from the gas generator, the piston having a proximal end facing the gas generator, a distal end facing the driving element, a central transverse plane located between the proximal end and the distal end, and an outer surface, the proximal end and the distal end each having a portion indented inward to respectively define a proximal concave depression and a distal concave depression, the proximal concave depression forming a proximal flexible rim that expands circumferentially outward when the pressurized gas from the gas generator enters the proximal concave depression, the expansion of the proximal flexible rim forming a proximal seal for resisting gas leakage beyond the proximal end of the piston, the distal concave depression forming a distal flexible rim that expands circumferentially outward when backpressure from the driving element is applied to the distal concave depression, the expansion of the distal flexible rim forming a distal seal for resisting gas leakage beyond the distal end of the piston;
• wherein the outer surface comprises two truncated generally conical surfaces, wherein the truncated generally conical surfaces have a common base, and wherein the common base coincides with the central transverse plane of the piston the piston having a larger outer diameter in the central transverse plane than in any transverse plane intersecting one of the proximal concave depression and the distal concave depression, the diameter of the surface of the piston in the central transverse plane providing sealing between the piston and the tube, wherein the proximal flexible rim, the distal flexible rim, and the common base form a temporary triple seal in the tube when exposed to the pressurized gas and to the backpressure from the driving element.