Seat belt retractor

1. A seat belt retractor comprising:

a spool for winding up a seat belt,

a locking mechanism having a locking member that is prevented from rotating in a belt withdrawing direction in the event of an emergency, and

a seat belt load limiting mechanism for limiting load applied to the seat belt when the spool rotates relative to the locking member, the load limiting mechanism comprising:

a torsion bar that rotationally connects the spool and the locking member and is torsionally deformable when the spool rotates relative to the locking member, and

a shearing member that is disposed to extend both in the spool and the locking member, the shearing member being shear-deformable when the spool rotates relative to the locking member,

wherein at least a portion of the area of the shearing member positioned in the spool is fixed to the spool in the axial direction.

2. A seat belt retractor as claimed in claim 1 , wherein the shearing member is a shear pin, and the portion of the shear pin fixed to the spool is a screwed connection.

3. A seat belt retractor as claimed in claim 2 , wherein the shear pin has a notch groove formed therein which is adapted to be sheared.

4. A seat belt apparatus comprising:

a seat belt for restraining an occupant;

a tongue slidably supported by the seat belt;

a buckle fixed to a vehicle floor or a vehicle seat and to which the tongue can be detachably latched; and

a seat belt retractor including a spool for winding up a seat belt,

wherein the retractor further includes a locking mechanism having a locking member that is prevented from rotating in a belt withdrawing direction in the event of an emergency, and a torsion bar that rotationally connects the spool and the locking member and is torsionally deformable when the spool rotates relative to the locking member, and a shearing member that is disposed to extend both in the spool and the locking member, the shearing member being shear-deformable when the spool rotates relative to the locking member, wherein at least a portion of the area of the shearing member positioned in the spool is fixed to the spool in the axial direction;

wherein the retractor is actuated in an emergency to prevent the withdrawal of said seat belt.

5. A seat belt apparatus as claimed in claim 4 , wherein the shearing member is a shear pin, and the portion of the shear pin fixed to the spool is a screwed connection.

6. A seat belt apparatus as claimed in claim 5 , wherein the shear pin has a notch groove formed therein which is adapted to be sheared.

7. A seat belt retractor comprising:

a spool for winding up a seat belt and a locking member that is prevented from rotating in a belt withdrawing direction in the event of an emergency, and

a torsion bar for limiting load applied to the seat belt when the spool rotates relative to the locking member, the torsion bar rotationally connected to the spool and the locking member and is configured to deform when the spool rotates relative to the locking member, and

a shearing member that is disposed to extend both in the spool and the locking member, the shearing member being shear-deformable when the spool rotates relative to the locking member, wherein at least a portion of the area of the shearing member positioned in the spool is fixed to the spool in the axial direction.