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Safety Nets

Safety Nets

Automotive safety has come along way since drivers first started buckling up a half century ago.

But safety systems still have a long way to go. Even with increasingly advanced air bags and crash management technologies, more than 42,000 drivers perished on American roads in 2001, the most recent year for which the federal government has compiled fatality statistics. To that deadly tally, add many more thousands of injuries. Consumers have taken notice and have become eager readers of government and independent safety ratings.

With safety information increasingly influencing buy decisions, advanced safety systems now promise to push their way into more segments of the auto industry than ever.

In the future, automotive safety systems will act preventively, using advanced electronics to avoid crashes in the first place. "Smarter, smarter, smarter" is how Mary Fitch, manager of advanced occupant systems for Delphi Safety and Interiors (www.delphi.com/automotive), describes the evolutionary path for such safety systems. Airbags and seatbelts that adapt to occupant and crash conditions already show some smarts. The ultimate step, in Fitch's view, are "anticipatory" systems. "If we had perfect knowledge, we'd be able to deploy an airbag before the crash takes place," she says. "That's a long way off." But some existing driver-convenience features, with sensor and software enhancements, could help prevent crashes. Tim Tiernan, senior manager for driver awareness at Visteon Corp. (www.visteon.com), outlines a similar future. For example, he predicts adaptive cruise control will soon take on a safety role. To make automatic speed adjustments, these systems already use cameras and sometimes radar to track nearby vehicles. "We already have an eye out the world," he says, explaining that the next logical step is using that information to avoid crashes or trigger some "pre-crash" actions such as an occupant positioning.






Safety Advances: Inflatable systems are starting to move beyond frontal and side-curtain airbags. For example, DuPont Automotive has been working on inflatable systems based on its Hytrel polyester elastomers. These include inflatable floor mats and drive repositioning systems, below as wel as thorax protection system that would integrate into the door module above.

For now, however, accidents still happen. So safety engineers are working hard on new crash mitigation systems and improvements to existing ones. Their goal: Lessen the damage from collisions while keeping costs low and packaging difficulties to a minimum.

More Blow Ups

With good seatbelts and frontal airbags already standard and side-curtain airbags appearing in more and more vehicles, safety engineers have started to focus more of their design skills on crashes that are serious, though not necessarily deadly. And independent crash testing highlights this need. Offset crash tests, for example, "show more encroachment into the leg area than earlier frontal crashes," says Mark Schuchardt, a senior design engineer with DuPont Automotive (www.dupont.com/automotive). Mechanical systems-such as seat belts with adaptive tensioning and whiplash-prevention systems-no doubt play a role in injury prevention. But many of the latest interior safety concepts involve low-profile airbags that put a few extra inches between the occupant and the source of the impact.

These include deployable knee bolsters and inflatable floor mats for lower leg protection. Other systems reposition drivers in a crash offer added protection for the thorax in side impacts, or restrain the head in rear-end collisions. Some of these ideas have been around for years in the technical literature, notes Schuchardt. And some have gone into limited production. But making these systems more widely available comes down to cost and packaging.


Pedestraian safety also set maximum forces for upper leg and head impacts. Instead of raising hool lines to put a cushion between the hood and engine block, suppliers are working on deployable systems. Some woudl raise the hood in the event of a crash. Others, like this concept from DuPont, would add a ruggedized exterior airbag to the car.

New plastic designs might help alleviate both problems. DuPont, which in March launched a new business unit dedicated to applying all the company's materials know-how to automotive safety, has come up with several concepts for interior airbags made from Hytrel polyester thermoplastics elastomers. Unlike traditional airbags, though, these systems would use a low volume of gas to fill relatively flat bladders that unfold more than they inflate. Schuchardt says these bladders would typically extend to about 100 mm or so to offer an extra deceleration cushion. "A bigger cushion is possible if we go to a bellows or a collapsing geometry," he says, adding that some of the designs could be reset in the way that bendable soda straws extend and retract.

Describing these low-profile bladders in terms of mechanical properties, Schuchardt says the elastomer works well just for its elongation-though that property helps avoid brittle failures. Instead, flex-fatigue performance is what counts in this application since the elastomer bladder relies on molded-in hinge points. And he argues that polyester elastomers have a proven balance of properties for airbags. These include resistance to temperature extremes, colorability, and abrasion resistance. The material can also be blow-molded in a variety of shapes, allowing it to conform to different packaging requirements.

The inflatable floor mats may best illustrate the suitability of polyester elastomer for non-traditional airbags. Schuchardt notes that they would need plenty of abrasion, chemical, and temperature resistance to hold up to all the foot traffic. The ability to blow mold the mats would allow the mats to conform to different floor shapes. He also envisions designs that wrap up the side of the footwell or extend past the pedals.


Upcoing European safety requirements would force design changes to minimize the harm donewhen cars hit pedestrains. The regulations spell out specific targets for leg impacts -825 joules maximum during a 25 mph test -- and could force front end changes. This concept from GE Plastics tailors the company's thermoplastic energy absorbers to impact levels required for lower leg protection.

Of course, plastics won't be the only important material for the new deployable systems. Engineers at AutoLiv North America (www.autoliv.com) have come up with systems based on steel boxes that expand with a pyrotechnic charge. The company uses just such a box in its system for occupant repositioning. Located inside the lower seat cushion, the box expands during the crash, creating a ridge that prevents the occupant from "submarining," or sliding off the seat in a crash. AutoLiv has proposed expandable steel boxes for inflatable knee bolsters too-though the company's current implementation use steel panels backed by an air bag. The company uses steel in the knee area "for the same reasons it's used in other automotive structures," says Patrick Jarboe, former director of advanced engineering and now communications director for AutoLiv. He cites steel's strength, stiffness, and energy-absorbing nature. The knee bolsters show just how important the latter two properties can be. Jarboe explains that the knee's relatively small surface area and the high forces in the leg area during a frontal crash call for a stiff material like steel. He does, however, acknowledge that glass-filled thermoplastics also do the trick if the panels are designed for plastics upfront.

Other interior safety components may use a combination of materials. DuPont engineers have been working on steering wheels that combine steel stampings with overmolded crystal-line thermoplastics. They have also worked out pillar and door concepts that integrate thermoplastic crush-cones to perforated metal stampings. Both ideas aim to advantage of metal's strength and ductile failure mode and plastics' design freedom, which can be useful when integrating functions.

People Catchers?

Upcoming European regulations that boost pedestrian safety-a big issue on that continent's narrow streets-could influence on American cars as early as 2005, partly because of the global nature of car manufacturing and partly because of product liability risks. That prospect has already prompted safety system and materials suppliers to devise concepts that can minimize potentially negative effects on cost and styling. The head impact portion of the requirement, for example, could force automakers to put some space between hoods and the unforgiving mass of the engine block.

To meet the safety requirements without raising hood lines, automakers could instead use some sort of deployable hood that rises on impact to meet the pedestrian. AutoLiv has come up with just such a concept. Jarboe reports that it's based on a hood hinge assembly that incorporates an accordion-like steel box, pyrotechnically actuated, that raises the back edge of the hood upon impact. Other suppliers, like DuPont Automotive, have focused on rugged exterior airbags.

The leg injury portion of the regulation poses design problems of its own. To make way for extra energy-absorbing materials using conventional bumper construction, front ends might have to protrude more than automakers would like. Alternative energy-absorbing systems, however, promise to minimize the effects on styling. One such system comes from Pittsfield, MA-based GE Plastics (www.geplastics.com). Rather than olefin foams found in many bumper systems, GE has fashioned energy absorbing crush zones from Xenoy PC/PBT that has been injection-molded into corrugated and web-like geometries. The system has most recently seen use in the rear bumper of the Honda Element, reports Stephen Shuler, GE's global technology manager for bumper systems.

Until now, these thermoplastic energy absorbers have targeted the impact forces experienced during frontal and rear-end collisions between vehicles. "Pedestrian safety requires a very different level of impact," says Shuler, who cites forces of 825 joules for lower leg protection in 25 mph crash tests versus several thousand joules in a full-vehicle crash test at a similar speed. "The challenge is to do both in one component that doesn't affect styling," he says. To meet that challenge, GE has modified its proven energy absorber, molding in a zone tailored to the forces required for lower leg protection. As an add-on to an existing front end, this pedestrian safety zone would take up some space-about 80 to 120 mm, estimates Dirk Noordegraaf, a GE technology leader for air bags, instrument panels, and front-end structures. New designs, however, could take advantage of plastics' ability to integrate functions, wrapping the new pedestrian crush zone, the vehicle-level energy absorbing zone, and even bumper beams into a single injection molded part. "The effects on styling and cost from this integrated solution would be minimal," Noordegraaf says.

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