Maximum Impact

DN Staff

March 3, 2003

12 Min Read
Maximum Impact

"Cover your ears," Tom Vos, director of safety system technology at TRW, warns me. TRW engineers are evaluating a new air bag deployment strategy that they hope will reduce the risk of injury to out-of-position occupants (OOPOs), which includes children, small adults, and people who are too close to the air bag in a crash. We're about to witness a test that will measure chest compression, chest G's, head rotational acceleration, and a raft of other data associated with a crash involving a 108-lb, 4-ft 10-inch female that has just driven into a ditch, unbelted. The dummy is bald, and it (she?) is wearing a blue tank top and remarkably ugly shoes. They aren't somebody's cast-offs, Vos informs me. Dummy clothing and footwear is called out specifically in the Federal Motor Vehicle Safety Standards (FMVSS). There's a loud bang-and I blink. The next thing I see is a flaccid air bag, and the dummy sprawled in its seat, a faint wisp of smoke rising from its chest.

For the past 40 years, Tom Vos has been focusing on that almost infinitesimal amount of time that it takes for an automobile crash to occur, and all of the physics associated with it. During his long tenure, he has been actively involved in the development of occupant safety restraint technology-including seat belts, air bags, and integrated safety systems.

Moreover, he has been an influential force in the National Highway Traffic Safety Administration's (NHTSA) development of federal safety standards for motor vehicles, during a time when the regulatory environment could best be described as taking, "Two steps forward, one step back." "Things tended to go in six-year cycles. We'd be working on seat belts for awhile, and then we'd switch over to air bags, then we'd go back to seat belts because the requirements were delayed, and then we'd shift our focus back to air bags," recalls Vos. Though it was always disappointing to have a program cancelled, Vos remembers the early years of his career as an exhilarating time.

"Probably because of all of the program cancellations and delays, Tom gained a very in-depth understanding of all aspects of occupant safety systems. He knows the technology, and the interaction of all of the products together. He also understands the laws and why the laws were written the way they were. He's a tremendous asset not only for the technical community, but also is viewed by NHTSA as a repository of knowledge," says Kevin McMahon, VP of government affairs for TRW.

"Tom would come in here and explain the technology, and he was very cool and very knowledgeable and straightforward to deal with," recalls Bob Shelton, former deputy director of NHTSA who recently retired after a 25-year career with the agency. "He has this great ability to communicate complex engineering technical details in a way that everyone can grasp. It's not like you're talking to an engineer."

Vos credits his father for those communication skills or, as he puts it, his ability "to sell and promote" his ideas. "My dad was a minister, and maybe it was something in the genes but I learned the power of words and the importance of credibility." Always interested in how things work, though, Vos decided to study engineering at Oakland (MI) University. "It was affordable, and close to home," he says. "As a brand new institution, it was setting out to establish standards of distinction." He remembers many of his classmates flunking or dropping out under the pressure.

A combination of testing and simulation defines automotive restraint system design and reduces product development cycle times. As engineers gain a better understanding of crash dynamics, they are fine-tuning the roles that seat belts and air bags play in dissipating energy.

Ashtrays to Airbags

Since graduating in 1964 (student number 2,053), Vos has worked exclusively in the auto industry. Ironically, for an engineer who is described as "passionate about motorist safety," he got his start in the business at the Ternstedt Division of GM as a hardware engineer designing ashtray cover springs. His first safety-related project came when he was asked to design a seat belt retractor frame.

It was at this time that Congress began pressuring the automakers to introduce front seat lap belts as standard equipment. Ralph Nader had also just published his book, "Unsafe at Any Speed," which advocated use of the inflatable air bag. "Up until then, the prevailing notion was that people got into car accidents, and they got hurt," recalls Vos. "Very few were looking into causal factors." Only about 10% of drivers were wearing seat belts then, and 45,000 people a year were dying in traffic-related accidents. And the number was climbing.

Though the government was offering automakers the option of providing seat belts or air bags, the assumption was that air bags would ultimately replace seat belts. Vos says that he could see where air bags offered lots of promise, particularly with their ability to manage the occupant's rate of deceleration and dissipate energy, and he recognized the reluctance of the driving public to wear seat belts. So when GM pulled an air bag program out of Research at Fischer Body as a production development program, Vos jumped at the chance to sign on. "It was bizarre. Here we were working on this thing that would come bursting out of the instrument panel and save your life," recalls Vos.

Automatic restraint systems saves lives: As of 1999, 45% of the cars had airbags, and are credited by NHTSA with saving an estimated 4,758 lives.

The first U.S. air bag patent for automotive use was issued ten years prior, though never commercially developed. And there were still plenty of technical issues to grapple with. "One challenge was controlling the deployment of the air bag," recalls Vos. "In the 1960s, the bags were filled by releasing gas under high pressure-on the order of 3,500 psi."

First Patent for Vos

Particularly vexing was bleed down-gas would come rushing out of an orifice and into the bag, potentially resulting in a tremendous punch. Vos came up with a design that incorporated a second ignitor in an inner plug with a smaller cross sectional area to reduce the onset gas flow rate to the bag. Though GM never went into production with stored gases (industry went to a solid-propellant inflator introduced in the early 1970s), the design earned Vos the first of 13 patents-all in the areas of inflator design, propellant processing, and tailorable restraint systems.

How severe: Even a minor fender bender can exhibit the same dynamics as a severe crash in the first 5- ms. So predictive algorithms developed by TRW process crash dynamics information continuously, determining if and when seat belt pretensioner and air bag should be activated. It also could provide input to real-time performance tailoring.

In 1971, Vos left GM and joined the Hamill Division of Firestone, first as a research engineer investigating low-pressure stored gas inflators, pyrotechnic gas generators, and deployable instrument panels. Meanwhile, government was backing away from any air bag requirements.

With the technology on the back burner, Vos-now manager of seat belt and air bag product engineering-began to emerge as the technology's advocate. "I always joke that Tom is the eternal optimist, but he really does have this amazing ability to stay positive in the face of adversity," says Charlie Steffens, who hired in as an engineer in 1975 under Vos and is now director of systems engineering at TRW. "He was involved in the very first air bag programs, and he could see the potential in terms of what the technology could do, and he wasn't going to give up on it."

Vos snuck air bag research into every management proposal he wrote. Then, the Carter Administration ordered a phasing-in of passive restraints in 1977. Vos established separate engineering and research departments that designed, developed, and production-verified a sodium-azide (solid propellant) based air bag assembly. After TRW had produced only 50 units for a demonstration police fleet, the mandate was again rescinded. The dust had barely settled when the Supreme Court overturned the prior ruling.

"At this point, I said, 'Let's go for it, we can't afford not to be in it,'" recalls Vos. In 1983, he got the approval of Firestone (which was bought by TRW in 1984) to resurrect the air bag program and was promoted to manager, inflatable restraints. He tripled his engineering staff from 60 to 200-no insignificant feat, given the relatively few number of engineers with air bag experience. His team was the first in the industry to design, develop, and launch a passenger side pyrotechnic air bag system.

"Back in those days, there was no list of requirements, no set of specs, so we had to write them concurrently," recalls Bob Balsis, a senior project engineer who was first hired by Tom in 1975. "Tom really provided great leadership. He's very smart, he approaches problems analytically, and he's able to break complex problems down into first principles."

No one at this point, however, was actually thinking about the hockey stick effect-the rapid ramp-up in production volumes necessary for succeeding programs. The company was focused on resolving launch issues, and no one was addressing future requirements.

So Vos put together a proposal for establishing a green-field lab to conceive, prototype, and specify a continuous process method of producing air bag propellant. In 1992, he won a TRW Chairman's Award for designing, constructing, and launching a green-field plant complex for producing passenger side air bag propellant. The plant was production-verified just 11 months from the time the process was concept-verified at the prototype lab.

When their first customer, Ford, put in an order for 2 million air bags, TRW was ready.

Continuous Improvement

There's no question that air bags work. Overall, they are credited with a 12% fatality reduction for all occupants, belted or unbelted, in all crashes, and an even more significant reduction for certain types of crashes. But by 1996 it was becoming clear that there were problems with the technology, specifically with children and small adults, and NHTSA was trying to figure out how to address that issue. As a first step, the agency decided to change the test procedure for air bags to allow them to be less powerful, though the longer-term goal was clear: Advanced air bag technology that would retain the benefits while reducing the risk.

The mid-1990s also brought a growing awareness of energy management issues and the complementary roles that seat belts and air bags could play. Seat belts couple the occupant to the deceleration of the vehicle, which reduces the ultimate speeds and energy the restraint system would otherwise have to deal with. Air bags dissipate the occupant's kinetic energy by metering gases through vents and fabric wave. By considering the system as a whole, engineers were learning better how to maximize the dissipation of the occupant's kinetic energy.

Once again, Vos was at the frontlines of these development efforts, managing the complex math modeling, simulation, and crash testing of safety systems that determines the performance criteria for new products. In June 2000, he received his 13th patent, along with two other TRW engineers, for an inflatable vehicle occupant protection device module. Currently, he's focusing on advanced bag/belt systems and directing a team who is developing advanced sensing systems that will tailor system performance to occupant position/crash scenarios. He also continues to be the point man for regulatory and legal issues.

Reflecting back on his career, Vos considers himself lucky to have been part of an engineering community that had the opportunity to make a difference. "I've enjoyed a career filled with tremendous diversity in challenges, the support of bright and enthusiastic engineering teams, and all in the pursuit of improving public safety."

Anatomy of a Crash

TIME (ms)




Bumper contact

Occupant velocity= 30 mph relative to the ground; 0 mph relative to the car


Fenders/headlights into barrier

Ball sensor in seat belt retractor initiates locking movement


Front end - six inch crush

Occupant starts to translate pulling lock pawl into sprocket with 15-mm webbing extension


Crash sensor sends current to seat belt pretensioner and first stage of airbag inflator


Engine components involved in crash

Occupant lower torso movement resisted by lapbelt and upper torso/head begins to rotate; bags rupture tear seams and begin to deploy


Pretensions complete stroke and remove slack, accelerating the rise in belt tensioning


Engine and trans mounts break away

Bags fully deployed and pressurizing in front of occupants; Shoulder belt tension exceeds load limiter threshold and webbing begins to "meter" off the spool, allowing further forward movement of occupants


Vehicle coming quickly to a stop

Belt and seat yield, allowing of knees into bolster to supplement lower torso restraint; Load limiter is stroking, absorbing energy from the occupant while the occupant displaces half the bag volume, expelling the bag pressure through the vents


Vehicle stopped and some rebound off barrier

Occupant has rotated full forward and is now pulled rearward by the energy stored in the stretched seat belts and the remaining pressure in the bag; There is sufficient rebound energy to throw him back against the seat

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