Mercedes-Benz ESF Safety Car: More, Better, Smarter Airbags!

March 5, 2010

Last summer we wrote briefly about the Mercedes-Benz ESF-2009 experimental safety concept vehicle, including its remarkable under-car airbag, which deploys only during a crash to help slow it down.

It's a 2009 Mercedes-Benz S400 Hybrid full-size luxury sedan that's been fitted with several new and experimental devices to increase the car's passive safety during an accident.

Almost all of the technology shown will make its way into production cars at some point.

First since 1974

Yesterday, we spent two hours interviewing project manager Michael Fehring and climbing all over the car, which was built to revive the company's long tradition of high-tech safety prototypes, lapsed since 1974.

Some of the technologies aren't particularly visible, like automatic headlights that adjust the brightness of a "partial high beam" to compensate for oncoming vehicles.

But the most notable thing about the ESF may be its use of inflation technology in new and different ways. Not only does it have a full suite of airbags, plus some new ones, it uses gas cylinders to inflate both steel door beams and a large bag under the car.

Some highlights:

Mercedes-Benz ESF 2009 safety concept car, inflatable metal door side-intrusion beams

Mercedes-Benz ESF 2009 safety concept car, inflatable metal door side-intrusion beams

Enlarge Photo


Looking at ways to reduce the weight of the car, the ESF team created a new type of side-intrusion beam inside the door skin. Current beams must fit within the door skin, meaning they are heavily engineered to be strong within a very narrow space.

The startling innovation here was to create an inflatable steel beam, using the same gas cylinder that inflates current thorax airbags. By increasing the beam's diameter as much as 2 inches, the beam becomes structurally stronger using much lighter weights of steel.

The inflation is triggered by side-looking radar sensors, part of Pre-Safe 360, an all-around accident detection system. Only 20 to 30 milliseconds is needed to inflate the beam, which bulges out the door skin significantly--unimportant if a side impact is pending.

According to Fehring, each of the four new inflatable beams was 0.5 kilogram (1.1 pound) lighter than the current design, cutting almost 5 pounds of total vehicle weight.

mercedes benz esf 2009 experimental safety vehicle 008

mercedes benz esf 2009 experimental safety vehicle 008

Enlarge Photo


While front-passenger airbags are now standard in new cars, they're less than perfect. Unlike the driver's seat, where the need to steer keeps the driver a predictable distance from the steering wheel, passengers can adjust their seats far forward or aft--and they do.

The ESF team sought to make the passenger airbag smarter by using the seat position sensor to control how much the bag inflates. Four straps inside the bag control its thickness, keeping it smaller when the seat is far forward, but letting it fully inflate if the seat is back.

And this appears to be one ESF innovation that's close to showing up in Mercedes-Benz vehicles. Although he wouldn't say when, Fehring said the size-adaptive airbag "will come very quickly" into production cars.

An even nearer-term innovation is adjustment for the passenger's weight, based on a seat-compression sensor, by opening or closing a supplemental vent in the bag. Heavier passengers need "harder" bags, so the vent stays shut; lighter riders are cushioned by a "softer" bag whose gas escapes more quickly through the open secondary vent.

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