Airbags on the Outside

Gary S. Vasilash

Airbags are seemingly everywhere on the interior of vehicles. But what about on the outside? One day we could see them there, too.

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You’ve heard the phrase “in the blink of an eye.” But what you probably don’t know is just how long that really is.

According to Steve J. Peterson, director of global systems engineering for occupant safety, ZF TRW (, that’s about the entire time an airbag deployment takes from inflation to deflation: “Typically 20 to 30 milliseconds after impact you need to have the bag up and absorbing energy. By 100 milliseconds the event is over.”


And 100 milliseconds (ms) is about the amount of time that it takes to blink your eye. The whole thing goes so fast that it is something that you can’t really see.

Now in a frontal collision, there is generally a nontrivial amount of mass between the driver and front passenger that absorbs energy. Like the hood and fenders and structure beneath them, to say nothing of the powertrain. And vehicle engineers configure such things as frontal rails in the body-in-white structure such that energy is channeled so that there is less of it making its way into the cabin. There is a lot to work with, material-wise, to perform crash-energy management.

However, next time you get behind the wheel, take a look to your left. All that’s there are glass, fabric and a couple of layers of metal between you and the outside world. So in the event of a T-bone accident, there’s not a whole lot there.

About a third of vehicular fatalities are caused by side-impact collisions.

To be sure, there are nowadays ultrahigh-strength steel pillars (using hot-stamped boron steel for the B-pillar is seemingly de rigeur), rings and rails that help mitigate the consequences of such a collision. In addition to which there are side-impact airbags that are deployed.

But could there be more?

According to Peterson, a few years ago, in response to a study sponsored by the Spanish government to look into vehicular safety, ZF TRW developed an exterior side airbag. “We asked ourselves, ‘If we could reduce the energy that goes into the car, what would it look like?’”

So ZF TRW developed an airbag that was housed inside the rocker panel. There is a plastic container into which the bag is fitted. The bag material is similar to the nylon that’s used for interior airbags, though with a different coating and thicker. When the bag deploys, it comes up and over the rocker, up the side of the vehicle. Peterson describes it as “a pretty dramatic bag, about three times the size of a typical passenger bag.” This exterior side airbag has multiple chambers and multiple inflators to help assure that the bag deploys as required.

But a key issue, Peterson points out, is making sure that the bag deploys when required—and only when required.

When there is a typical airbag deployment, it is the result of crash sensors in the vehicle determining that, say, there is an exceedingly sudden deceleration, so it sends a signal to an electronic control unit, which then initiates the ignition of the airbag.

In other words, this happens after the fact.

With the external airbag, there is a different approach.

Peterson says that the development of sensor technology for autonomous vehicle application—cameras and radar, for example—can also be beneficially applied for the external airbag. The intent would be to use the sensors to determine, about 50 ms beforehand, that it is to the point of no return, that there will be a side collision and that the bag needs to be deployed. Obviously, there needs to be a high level of confidence that the collision will occur.

Peterson: “Our sensing technology for autonomous technology is constantly improving, and we would expect it will improve to the point that we will know an accident is coming to the point of no return.” He notes: "It takes maybe twice as long as a passenger bag to fill up, but you’re firing it before the impact.”

The preliminary results showed that there was a reduction of impact by about 30 percent compared with a setup that has a side airbag (internal) and seat belt (Peterson is emphatic about the importance of seatbelt use by every person in a vehicle, no matter where they are sitting: “Getting people to buckle up is the best thing you can do.”).

Peterson says that they’ve conducted feasibility studies and performed demonstrations for a couple of auto makers. Were the external bag to go into production, the timing would be sometime after 2020 and the initial application would be for luxury cars.

But he points out that as there is more work being done for autonomous vehicles in general, it will be important for there to be the outward looking sensors to be integrated with inside-looking cameras and the airbag systems in the vehicle. Realize that presently the position of people in seats is fairly defined, but there is the possibility that in the case of autonomous vehicles, seats may not always be oriented as they are now (e.g., the Mercedes F015 Concept, an autonomous vehicle, has front seats that rotate so that they can be rear facing). So Peterson says that it may be necessary to have airbags that preemptively, or before the actual collision, nudge people so that they are in a position to be best protected when the collision occurs.

As for the external bag: he admits that it is a “pretty wild idea.”

But it is a wild idea that can potentially save lives.