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Seat Belt Pretensioner offers simplified design..

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December 8, 2010 - SPR4 (Snake Pretensioner Retractor) uses plastic piston instead of metal components to transfer tensioning torque, resulting in simple and light weight design. Comprised mainly of piston, gas generator, tube, and pinion, uses tensioning concept that transfers power without limiting functionality. Pre-tensioning takes 10 msec, and green gas used exhibits low variation over temperature range. Also, tube is bent into dimensions of retractor without constraining seat belt webbing.

TRW Launches Its Next Generation Seat Belt Pretensioner

(Archive News Story - Products mentioned in this Archive News Story may or may not be available from the manufacturer.)

TRW Automotive
12025 Tech Center Dr.
Livonia, MI, 48150

Press release date: December 6, 2010

KARLSRUHE, Germany -- TRW Automotive Holdings Corp. (NYSE: TRW), the global leader in active and passive safety, has launched its next generation seat belt pretensioner to offer weight and packaging advantages to its worldwide customers. The SPR4 (Snake Pretensioner Retractor) 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.

Harald Lutz, director engineering, TRW seat belt systems said: "The pyrotechnical seat belt pretensioner has been an established product for nearly 30 years, but TRW has taken this concept to a new level. Based on our proven production seat belt retractor (ESA 4.0), the SPR4's design is simplified and a new tensioning concept transfers power without limiting functionality."

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 in to 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 ten milliseconds.

Lutz added: "Seat belt pretensioners need to generate tensioning torque quickly, accurately and reliably with a stable level of force and the innovative concept allows for this."

The new design offers vehicle manufacturers a number of advantages compared with existing systems. The lighter weight, plastic material allows the tensioning force to be generated more quickly than conventional systems. Secondly, the damping behavior of the plastic snake allows the initial peak when impacting the pinion to be significantly lower compared to conventional systems where two rigid steel elements impact on each other. This also results in less wear on the SPR4's components.

Moreover, the green gas shows favorably low variation over the temperature range and works reliably through a wide range of conditions.

The design of the SPR4 offers vehicle manufacturers greater flexibility in terms of packaging and space as it consists of only four main components: the piston, the gas generator, the tube and the pinion. The tube is bent into the dimensions of the retractor without constraining the seat belt webbing helping to further minimize installation space.

TRW's ESA 4.0 has been in production since 2001 on a number of key vehicle platforms. The new SPR4 will be ready for production in 2013.

About TRW

With 2009 sales of $11.6 billion, TRW Automotive ranks among the world's leading automotive suppliers. Headquartered in Livonia, Michigan, USA, the Company, through its subsidiaries, operates in 26 countries and employs over 60,000 people worldwide. TRW Automotive products include integrated vehicle control and driver assist systems, braking systems, steering systems, suspension systems, occupant safety systems (seat belts and airbags), electronics, engine components, fastening systems and aftermarket replacement parts and services. All references to "TRW Automotive", "TRW" or the "Company" in this press release refer to TRW Automotive Holdings Corp. and its subsidiaries, unless otherwise indicated. TRW Automotive news is available on the internet at

CONTACT: Lynette Jackson, (44) 121.506.5315,, Louise Colledge, (44) 121.506.5317,, John Wilkerson, +1-734-855-3864,, all of TRW Automotive
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