Patent ID: 8469301

Claim:
A seat belt retractor, comprising: a spindle configured to wind a seat belt; an electric actuator configured to cause the spindle to rotate; a pyrotechnic pretensioner coupled to the spindle to retract the seat belt by acting on the spindle; a power transmission mechanism that is configured to transmit power from the electric actuator to the spindle for rotating the spindle and that is configured to prevent power transmission from the electric actuator to the spindle upon operation of the pretensioner, wherein the power transmission mechanism includes: a first rotation member that rotates together with the spindle and has a first engaged section; an engaging member having a second engaging section that can engage with the first engaged section of the first rotation member; and a second rotation member that is joined to the electric actuator and has a groove section that holds the engaging member, such that the engaging member can move in the groove section between a first position at which the engaging member is positioned when the electric actuator is not operating, a second position at which the engaging member becomes positioned when the second engaging section engages with the first engaged section of the first rotation member through operation of the electric actuator, and a third position at which the engaging member becomes positioned on an opposite side to that of the second position across the first position upon operation of the pretensioner; and a return prevention mechanism that prevents the engaging member from returning to the first position and the second position after having moved to the third position, and wherein the return prevention mechanism comprises an annular spring member that, on account of a biasing force thereof, is held against a fixed ring protruding from a cover member and against a recess that is provided in the engaging member; and a projection that is provided on the second rotation member, such that the spring member climbs over the projection and moves when the engaging member moves from the second position to the third position across the first position as a result of operation of the pretensioner.