LIVONIA, Mich. – TRW Automotive Holdings Corp. is now delivering its next-generation SPR4 (Snake Pretensioner Retractor) seat belt assembly for its worldwide customers and is launching the product in North America, Europe and China.
 
The SPR4 uses a plastic piston instead of conventional metal components to transfer tensioning torque, resulting in a simpler and lighter-weight design as well as more compact packaging, the company says.
 
Norbert Kagerer, vice president of occupant safety systems engineering, TRW, said the design offers vehicle manufacturers a number of distinct advantages, which has led to strong interest globally.  
 
"The lighter-weight, plastic material allows the tensioning force to be generated more quickly than with conventional systems," Kagerer said. "Secondly, the damping behavior of the plastic snake allows the initial peak force, when impacting the pinion, to be significantly lower compared to conventional systems where two rigid steel elements impact on each other."
 
When vehicle sensors trigger the seat belt system, a pyrotechnical gas generator is ignited releasing a "green gas," which 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 usual steel balls. The pinion then transmits a significant torque to the belt retractor spool to pre-tension the seat belt. The whole process takes just 10 milliseconds, according to TRW.
 
The SPR4 will launch on a range of vehicles from small a-segment cars up to sport utility vehicles.