Patent ID: 7717215

Claim:
A seat belt retractor to be installed in a vehicle comprising: an electric motor; a spool driven by the electric motor, wherein the spool is capable of winding and unwinding a seat belt for restraining a vehicle occupant; a motor speed reduction mechanism to reduce the rotation speed of the motor via a plurality of gears positioned between a driving shaft of the electric motor and the spool; and a control mechanism to control the electric motor; wherein when the seat belt is worn by the vehicle occupant the control mechanism is configured to control the motor in a first setting mode before a vehicle collision, a second setting mode before a vehicle collision, and a third setting mode during the vehicle collision; wherein the control mechanism is configured so that in the first setting mode the electric motor is driven repeatedly to rotate in a belt winding direction and a belt unwinding direction to alternately produce a stronger belt tension and a weaker belt tension when an obstacle is detected or a warning mode is detected; wherein the control mechanism is configured so that in the second setting mode the electric motor is driven in a belt winding direction to apply a second setting tension on the seat belt, wherein the control mechanism controls the electric motor to operate in the second setting mode before a vehicle collision and after the first setting mode; and wherein the control mechanism is configured so that in the third setting mode the electric motor is driven in a belt winding direction to apply a third setting tension on the seat belt, wherein the control mechanism controls the electric motor to perform the third setting mode when the vehicle collision occurs.