Abstract: A seat belt pretensioner for a belt retractor includes a member that rotates relative to a frame of the belt retractor in response to a vehicle condition to rotate a spool of the belt retractor relative to the frame. A drive device rotates the member in response to the vehicle condition. The drive device applies a first torque to the member during a first stage of rotation of the member and the spool and applies a second torque greater than the first torque during a second stage of rotation of the member and the spool. A flexible drive member rotates the member relative to the frame. The flexible drive member extends around an axis of the member more than 360° after activation of the pretensioner.

Abstract: A seat belt pretensioner for a belt retractor includes a member that rotates relative to a frame of the belt retractor in response to a vehicle condition to rotate a spool of the belt retractor relative to the frame. A drive device rotates the member in response to the vehicle condition. The drive device applies a first torque to the member during a first stage of rotation of the member and the spool and applies a second torque greater than the first torque during a second stage of rotation of the member and the spool. A flexible drive member rotates the member relative to the frame. The flexible drive member extends around an axis of the member more than 360° after activation of the pretensioner.

Abstract: A seat belt retractor (10) includes a spool member (40) on which seat belt webbing (16) is wound. The spool member (40) is supported for rotation in a belt withdrawal direction (52) and an opposite belt retraction direction (54). The retractor (10) includes a plastically deformable torsion bar member (70) having a first portion (78) and a second portion (74). The second portion (78) of the torsion bar member (70) is rotatable relative to the first portion (74). The torsion bar member (70) twists upon rotation of the second portion (78) relative to the first portion (74). When the torsion bar member (70) twists, the spool member (40) rotates in the belt withdrawal direction (52) relative to the ratchet member (60), and the spool member cutter portion (92, 94) of the ratchet member cuts into the spool member (82, 84) to increase the resistance to rotation of the spool member relative to the ratchet member.