Safety belt pretensioner

A device for pretensioning a safety belt web joined to a reel mechanism in a vehicle, said device comprising:

• a cylinder,
• a piston displaceable in the cylinder and having a piston rod, the piston rod joined to one side of the piston and extending through an opening in one end wall of the cylinder,
• a motion-transmitting element acting between the piston rod and the reel mechanism, the element achieving rotations of the reel mechanism in the winding-up direction of the belt web upon displacement of the piston in one direction,
• a cylinder chamber having a pyrotechnic charge, the charge being able to cause, when detonated, a pressure increase in the cylinder chamber between the piston and a cylinder wall for displacement of the piston in one direction, and
• a controller for controlling the pressure in the cylinder chamber depending on the weight of a person held in by the belt,
• wherein the cylinder chamber is delimited between the side of the piston opposite to the piston rod and the second end wall of the cylinder, and
• wherein the motion-transmitting element is arranged to rotate the reel mechanism in the winding-up direction of the belt web when the piston is displaced in the projection direction of the piston rod,
• said cylinder chamber further comprising an outlet for communicating with a spill valve, said spill valve able to be set between various degrees of opening and a completely closed position.