The innovative system uses a plastic piston instead of conventional metal components to transfer tensioning torque through the torsion bar to the spool, resulting in a simpler design, more compact packaging and industry leading system weight.
The functionality of the SPR8 is such that when vehicle sensors trigger the seat belt system, a pyrotechnical gas generator is ignited releasing a gas that expands and builds up pressure in the guiding tube. This pressure acts on the snake-like plastic piston which is forcefully propelled into a pinion instead of the commonly used steel elements. The pinion then transmits a significant torque to the belt retractor spool to pre-tension the seat belt. The complete pyrotechnical system is sealed meaning no gas will be emitted during the pretensioning process, which altogether takes just ten milliseconds.