STOCKHOLM, Sweden, April 3, 2002 (PRIMEZONE) -- Autoliv Inc. (NYSE:ALV) (SSE:ALIV) has started to introduce a seat belt system which can adapt its restraining force - and hence the load on the occupant - to the severity of the crash and to the restraining force of the airbag. In future vehicles this technological breakthrough will also enable the seat belt to adjust its restraining force to each occupant.
This smart seat belt will be particularly beneficial for the elderly and for small women. The new improvement is currently being introduced globally on the new BMW 7-series and the new Mercedes E-Class.
High chest loads and rib fractures is a growing concern, since the population of elderly car occupants is increasing and the rib cage of a 60-year occupant can only take half as much load as the body of an individual in his twenties. Already in 1995, Autoliv helped address this issue by introducing seat belts with static load limiters. This mechanism allows the seat belt retractor to release a little webbing in a controlled manner before the load on the occupant becomes dangerously high. The airbag with its larger surface area is used instead to absorb a greater part of the crash energy. Six years after the initial launch, almost all of Autoliv's customers use this improvement in their front belt systems.
Together with BMW and Mercedes, Autoliv is now introducing load limiters that can apply two different restraining levels. Depending on which sensor or sensors that are used, the load on the occupant can therefore be adjusted to the circumstances of each crash, such as the size and position of the occupant and the crash severity.
"We have equipped the retractor in our smart seat belt with a gear box," explained Autoliv's project leader Gunter Clute. "In a crash, our smart seat belt starts - as in most modern seat belt systems - by tightening the belt up to 15 cm, using a pyrotechnic pretensioner. This eliminates slack and makes it possible to release some webbing at a later stage, if the load on the occupant becomes too high.
"In a traditional system, the loads to the occupant from the seat belt and the airbag are added to each other when the bag also starts to restrain the occupant. But in our smart seat belt, the system just shifts into the second, lighter gear to maintain the restraining force at a relatively constant level," he continued.
"In addition," Mr. Clute added, "the smart seat belt can adapt its restraining force - and hence the load on the occupant - to the crash severity. In a very violent crash the smart seat belt just stays in the first gear a little longer before it shifts into the second, lighter gear. And if the car has an occupant classification system, the smart seat belt can also adjust itself to each individual. Since many women are more susceptible to high belt loads than the average person, and these individuals do not need the same restraining force as a larger occupant, our latest seat belt enhancement could be especially important for female occupants," concluded Autoliv's project leader.
Technical Description
The gear box in Autoliv's smart seat belt consists of a torsion bar in which the belt is attached at one end. The bar is designed to twist when the load on the bar exceeds a pre-determined level. The bar has two sections with different diameters to produce two levels of torque. A metal tube can be moved and coupled onto the thicker or the thinner section of the bar, thereby changing the torque and the resulting restraining force.
In the initial phase when the occupant is only being restrained by the seat belt, the load limiter is in its higher torque setting. When the occupant reaches the airbag, the load limiter shifts into second gear by coupling the metal tube to the thinner section of the torsion bar. This is done by a small pyrotechnic charge.
The change of gear can be varied within a relatively wide time span. In a milder crash, it may be enough to run the smart belt system in first gear for only 40 thousandth of a seconds before shifting to the lighter torque. In a really violent crash, however, the change of gear should to take place later, often 70-80 thousandth of a second after the crash started.
When the triggering of the load limiter is tuned to the severity of the crash, the same sensors that control the frontal airbags are used. But the software programming of the airbag control unit has to be upgraded.
Illustrations: www.autoliv.com, under section "News"
Autoliv Inc. develops and manufactures automotive safety systems for all major automotive manufacturers in the world. Together with its joint ventures, Autoliv has close to 80 facilities with over 30,000 employees in 29 vehicle-producing countries. In addition, the company has technical centers with 20 crash test tracks in nine countries. Sales in 2001 amounted to US $4 billion. The Company's shares are listed on the New York Stock Exchange (NYSE:ALV) and its Swedish Depository Receipts on the OM Stockholm Stock Exchange (SSE:ALIV).
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