# US 8,770,506 B2 · High seal retractor pretensioner piston > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,770,506 B2 - Document ID: US8770506B2 - Status: Granted - Kind: B2 - Application number: 12/950,385 - Filed: 2010-11-19 - Published: 2012-01-12 - Granted: 2014-07-08 - Earliest claimed: 2010-07-06 - Assignees: Autoliv ASP, Inc. - Applicants: Jon Burrow; Gerald Keller - Inventors: Jon Burrow; Gerald Keller - Web page: https://patentgrep.com/patent/US8770506B2 ## CPC - B60R 22/4628: {characterised by fluid actuators, e.g. pyrotechnic gas generators (actuating a cable B60R22/4619)} - B60R 2022/4642: {the gas directly propelling a flexible driving means, e.g. a plurality of successive masses, in a tubular chamber} - B60R: VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR ## Abstract A pretensioner assembly for motor vehicle belt restraint systems is provided. The pretensioner assembly includes a tube in fluid communication with a gas generator. An elastic piston disposed within the tube is operable to drive a plurality of balls upon receiving pressurized gas discharged from the gas generator. The piston includes a proximal end and a distal end. The proximal end includes a flexible rim that expands upon receiving pressurized gas from the gas generator, and the distal end includes a flexible rim that expands in response to backpressure from the plurality of balls. The expansion of the flexible rims at the proximal and distal ends of the piston provides a tight seal between the piston and the inner peripheral wall of the tube. ## Claims ### Claim 1 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. ### Claim 2 (depends on 1) The pretensioner assembly of claim 1, wherein the piston includes a discrete seal bead protruding from the outer surface of the piston in the central transverse plane. ### Claim 3 (depends on 2) The pretensioner assembly of claim 2, wherein the discrete seal bead forms a contact seal with the tube for preventing gas from leaking beyond the central transverse plane of the piston. ### Claim 4 (depends on 1) The pretensioner assembly of claim 1, wherein the piston is composed of an elastic polymer. ### Claim 5 (depends on 1) The pretensioner assembly of claim 1, wherein the driving element includes a plurality of balls operable to rotate a spool for pretensioning the seatbelt webbing. ### Claim 6 (depends on 1) The pretensioner assembly of claim 1, wherein the proximal concave depression includes a proximal section and a distal section, the proximal section forming a generally frustoconical space, and the distal section forming a generally cylindrical space. ### Claim 7 (depends on 1) The pretensioner assembly of claim 1, wherein the distal concave depression includes a distal section and a proximal section, the distal section forming a generally frustoconical space, and the proximal section forming a generally cylindrical space. ### Claim 8 (depends on 1) The pretensioner assembly of claim 1, wherein the piston includes a longitudinal axis of symmetry and a plane of symmetry, the plane of symmetry formed by the central transverse plane bisecting the longitudinal axis of symmetry. ### Claim 9 (depends on 8) The pretensioner assembly of claim 8, wherein the outer surface has a radius about the longitudinal axis of symmetry, and wherein the radius of the outer surface generally decreases from the central transverse plane to the proximal and distal ends of the piston.