Seat belt retractor with assist spring

In a vehicle occupant restraint belt retractor having a belt reel rotatably supported on a housing, and a belt wound and unwound between a limit of belt winding and a limit of belt unwinding during rotation of the reel, a spring mechanism for biasing the reel in the belt winding direction of rotation comprising:

• a primary winding spring acting between the reel and the housing and being wound up during belt unwinding reel rotation to store energy for biasing the reel in the belt winding direction, an assist spring housing mounted for rotation relative the housing and the reel, an assist spring acting between the reel and the assist spring housing, locking means carried by the assist spring housing and selectively actuatable between a first position connecting the assist spring housing with the housing so that the assist spring is wound up during belt unwinding reel rotation to store energy for biasing the reel in the belt winding direction and a second position connecting the assist spring housing with the reel so that the assist spring is maintatined at its then existing state of winding and has no biasing affect on the reel, and lock operating means being effective to sense the extent of belt unwinding to move the locking lever between the first and second positions in response to the extent of belt unwinding so that during belt unwinding within a predetermined range relative the limit of belt winding the lock lever is in the first position to effect wind up of the assist spring and assist the primary spring in biasing the reel in the belt winding direction of rotation and the lock lever is in the second position during belt winding and unwinding not within the predetermined range so that the assist spring is maintained at its then existing state of winding with no biasing affect on the reel.

In a vehicle occupant restraint belt retractor having a belt reel rotatably supported on a housing, and a belt wound and unwound by rotation of the reel between a limit of belt winding and belt unwinding, a spring mechanism for biasing the reel in the belt winding direction of rotation comprising:

• a winding spring having one end attached to the reel and the other end attached to the housing and being wound up during unwinding reel rotation to store energy for biasing the reel in the winding direction, an assist spring housing mounted for rotation relative the housing and the reel, an assist spring having one end connected to the reel and the other end connected to the assist spring housing, a lock lever pivotally mounted on the assist spring housing for movement between a first position engaging the housing to effect wind up and storage of energy in the assist spring during unwinding reel rotation and causes the assist spring to bias the reel in the winding direction and a second position connecting the assist spring housing with the reel so that the assist spring housing and the lock lever rotate in unison with the reel and the assist spring is maintained at its then existing state of winding with no biasing affect on the reel, a timing member rotatably mounted in the housing, drive means acting between the reel and the timing member and effective to rotate the timing member through less than one revolution relative the housing as the reel makes a plurality of revolutions between the limits of belt winding and belt unwinding, an actuating lever pivotally mounted on the timing member and being engageable with the lock lever to effect movement of the lock lever between its first and second positions, and a cam means on the housing cooperable with the actuating lever for controlling pivotal movement of the actuating lever so that during a predetermined number of belt unwinding revolutions of the reel from the limit of belt winding the lock lever is maintained in its first position connecting the assist spring housing with the reel housing to wind up the assist spring and then during further unwinding revolutions beyond the predetermined number the actuating lever moves the lock lever to the second position so that the tension of the assist spring is maintained at its then existing state by causing the assist spring housing to rotate with the reel, said cam means being further effective to restore the lock lever to the first position upon belt winding reel rotation to within the predetermined number of revolutions of the reel from the limit of belt winding so that the assist spring provides a winding bias on the reel to assist the winding spring in effecting completion of winding of the belt on the reel.