Belt pre-tensioning device

The belt tensioner drive has a drive unit (3) which drives a screw shaft (13) whose worm gear (10) is fixedly mounted on a torque screw (12) and is rotatably mounted on a winding shaft (4). The torque screw has a tooth portion (a) which is positioned and is meshed with an output gear (11). The gear portion (a) of torque screw is arranged adjacent to tooth portion (b). The axial displacement of the torque screw is formed between two preset positions (I) in which the output gear is meshed to torque screw through gear portions (a,b), based on axial force input into the torque screw.