There is a cynical adage in the motor industry that driver visibility is essential because “people like to see what they are going to hit.”
Despite huge advances in primary and secondary visibility, there continues to be constraints on further improvement caused by the often conflicting requirements of vehicle design and structural integrity, including the thickness of the A-pillar—a vital aspect of crashworthiness. But now, Autoliv has come up with a potential solution: an expandable pillar.
It is the idea of Active Body Structures specialist Dr. Bengt Pipkorn: “We have been working on the project for two years and test results have been very good.”
Autoliv’s long experience in airbag design and manufacture has provided a technology foundation for the project, which follows other attempts to reduce A-pillar intrusion on driver vision, including an open-girder style concept by Volvo.
Autoliv is working on the expandable A-pillar solution with Saab. It allows the pillar to be slimmed down to only 23 mm (0.9 in), about three times thinner than a typical pillar, while providing required crash energy-absorbing capability. And it could give a car the sort of chic visual effect that the 1955 Citroën DS 19 achieved with its slimline, set-back A-pillar design.
Benefits not only include improved visibility and aesthetics but also reduced weight, additional design freedom, and a reduction of roof intrusion in the event of a rollover or serious high energy offset collision. Very violent offset frontal crashes can cause the A-pillar to bend and the passenger compartment to collapse, said Pipkorn.
“We have a completely new design that forms part of the body-in-white (BIW),” he explained. “The pillar uses high-grade but not high-strength steel. The structure is folded and welded airtight, with a gas generator at one end. In the event of a serious crash, the generator is activated and the steel unfolds and expands, the added cross-section giving the required added strength.”
The possibility of using expanding structures in vehicles and other applications is not new; it dates back to the 1970s, said Pipkorn.
But the challenge for its use for automotive applications was to achieve comprehensive integration and achieve essential integrity. Modern design techniques and electronics now make this a reality, and while the Autoliv system is still in development, Pipkorn is confident that it will be suitable for production.
It would add some cost to a vehicle—most of it down to the gas generator—but that would be relatively modest, according to Pipkorn. The system could be easily absorbed into the manufacturing process; a mounting is needed for the generator and cabling and connections are needed. “But from a production point of view, it is quite straightforward because it is part of the BIW, not an add-on,” he said.
Driver vision angle improvement is put at typically 25% when compared to current state-of-the-art pillars, and despite the need for the generator and associated elements, weight saving is about 10%. Expansion of the width of a 23-mm pillar to 73 mm (2.9 in) in an accident increases stiffness by some 45% in 10 milliseconds, based on Autoliv’s simulated and real tests.
Pipkorn says the system could be used for any type of vehicle, including SUVs, sports cars, and city designs. Potentially, it gives designers new freedom to create distinctive, step-change glasshouse aesthetics, particularly introducing a further aspect to future electric-vehicle styling, while enhancing safety.