Reversible seat belt tensioner

Abstract

A reversible seat belt tensioner includes an electric motor ( 2 ), a belt shaft ( 1 ) drivable in the belt winding direction by the electric motor ( 2 ) via a drive wheel ( 10 ), and a drive shaft ( 9 ) transmitting the rotational movement of the electric motor ( 2 ) to the drive wheel ( 10 ). The drive shaft ( 9 ) is connected to at least one of the drive wheel ( 10 ) and the electric motor ( 2 ) via a helical gear unit. The teeth of the helical gear unit make point-shaped contacts with each other, and the drive shaft ( 9 ) is axially movable relative to the electric motor ( 2 ) or the drive wheel ( 10 ) without disengaging the gear teeth.

What is claimed is: 
     
         1 . A reversible seat belt tensioner comprising:
 an electric motor generating a rotational movement,   a belt shaft drivable in a belt winding direction by the electric motor via a drive wheel, and   a drive shaft transmitting the rotational movement of the electric motor to the drive wheel,   wherein the drive shaft is connected via a helical gear unit to at least one of the drive wheel and the electric motor, the helical gear unit having helical gears with gear teeth and allowing an axial movement of the drive shaft relative to the at least one of the drive wheel and the electric motor without disengaging the helical gears, the teeth of the helical gears making point-shaped contacts with each other.   
     
     
         2 . The reversible seat belt tensioner according to  claim 1 , wherein the axes of rotation of the drive shaft and of the electric motor are arranged at a first angle with respect to each other and the axes of rotation of the drive shaft and the drive wheel are arranged at a second angle with respect to each other and wherein the first and second angles are identical, and wherein the axes of the electric motor and of the drive wheel are arranged parallel to each other. 
     
     
         3 . The reversible seat belt tensioner according to  claim 1 , wherein the drive shaft is connected to the electric motor and the drive wheel via a respective helical gear unit, and wherein the gear units on the drive shaft are arranged axially offset with respect to each other. 
     
     
         4 . The reversible seat belt tensioner according to  claim 1 , wherein the drive shaft is arranged between the axes of rotation of the electric motor and of the drive wheel. 
     
     
         5 . The reversible seat belt tensioner of  claim 1 , wherein the electric motor generates a rotational movement of a motor shaft with a first helical gear, the belt shaft is drivable in a belt winding direction by the electric motor via the drive wheel with a second helical gear with a larger diameter than the first helical gear, wherein the drive shaft transmitting the rotational movement of the electric motor to the drive wheel has a third helical gear meshing with the first helical gear, and the drive shaft further has a fourth helical gear axially offset from the third helical gear and meshing with the second helical gear,
 wherein the motor has a first axis of rotation, the drive shaft has a second axis of rotation, and the drive wheel has a third axis of rotation, the first and third axes of rotation being parallel to each other and the second axis of rotation intersecting with a plane containing the first and third axis of rotation between the first and the third axis of rotation.   
     
     
         6 . The reversible seat belt tensioner according to  claim 1 , wherein the drive shaft and each of the at least one part have an axis of rotation, and the axes of rotation are arranged with respect to each other at angles that are acute or obtuse.