Benz shapes the safety future

Just when you thought you had airbags, stability control and antilock brakes figured out, Mercedes-Benz has ramped up its road-safety engineering with the ESF 2009 safety research vehicle.

Mercedes Benz's ESF 2009 safety car (more here) enters new safety territory by doubling a normal car's emergency braking power, improving side impact safety with expanding metal 'airbags' inside the doors, automatically lighting up pedestrians and animals at night, pushing passengers towards the middle of the car away from danger -- and even talking to other cars! Plus, in what is sure to be a boon for parents, the ESF 2009 even has a roof-mounted camera that can show snapshots of rear-seat behavior on a multi-media screen, while also debuting an all-new modular child seat. Benz says both child-focused safety devices could be in production in the very near future.

Timed to coincide with the global Advanced Safety of Vehicles Conference in Stuttgart, Mercedes-Benz gave the Carsales Network a sneak preview at its facility in Sindelfingen, Germany, to make the point that current vehicle safety is still well short of what is possible.

Mercedes-Benz has had thousands of safety engineers working away on technology to help avoid crashes (such as new LED headlight technology and car-to-car communications) and to maximise safety in unavoidable collisions.

"The primary aim is to prevent accidents in the first place," said Professor Doctor Rodolfo Schöneburg, who is the German company's Director of Passive Safety, Durability and Vehicle Functions.

"Where this is not possible, the aim is to mitigate their effects. The 'Magic Moment' for passive safety innovations is 600 milliseconds before the impact and we use this time to significantly increase occupant protection.

"But we approach both of these goals without increasing the weight, restricting practicality or compromising the autonomy of the driver. The driver drives and the car provides support."

Built in just eight months, the ESF 2009 is based around the new S400 Hybrid limousine (more here). It also includes a new combined seat belt and airbag for the back seat, sensors that can detect a collision from any direction and airbags to stop the people in the front seats from colliding with each other.

That there is no end to the development and refinement of safety systems is a tenet of Mercedes-Benz. Indeed, it wouldn't be a new Benz model if it didn't introduce a new safety feature -- be it minor or major. Here's a rundown of the future safety technology, Mercedes is working on... Some of them could be new production Mercedes models quicker than you think...

A normal S-Class fitted with Mercedes' Pre-Safe Plus technology uses three different radar systems to detect crashes. If you ignore all its warnings and the computers are convinced you're about to crash, it will automatically slam on the brakes, decelerating as hard as the brakes and tyres can manage.

There is a limitation to this effect, however, because the tyres have only so much rubber on the road and even good cars will only decelerate at around 1g -- 10 metres per second squared.

The Braking Bag concept is being developed with key supplier Continental and can more than double stopping power by setting off an airbag under the engine, which pushes a grippy, rubber-lined version of the sump guard directly onto the road, washing off speed at up to 2.5g!

But it's a once-only affair, and can only be set off in an unavoidable crash. And, because the bag pushes the car's nose up off the ground, the timing has to be perfect.

"The key is that energy is not only reducible at the wheels," Schöneburg said.

"We have to find the right time to inflate the bag -- and it's about 100-200 milliseconds before the crash. At 50km/h, that would be roughly 10 metres. Too early is counter-productive and too late is obviously too late.

"It's only to be used when you have an unavoidable accident and our sensors already tell us that. We know 600 milliseconds before whether we can avoid the crash or not.

"We see the crash with the sensors and at 5-7 milliseconds, the car knows whether it's a front, or side, or rear crash."

Given how critical its timing and performance will be, you'd expect more new technology to be at work here, but the Braking Bag uses existing airbag technology -- with a twist.

"This airbag inflates in 5 milliseconds, where a normal 60-litre driver airbag needs 15-20 milliseconds," said the Brake Bag's inventor, Karl-Heinz Baumann of Benz's Passive Safety Concepts and Strategy department.

"But this one isn't folded like a normal one. Because of where it is, it's flat and it's fast. We can detect an unavoidable crash in 5-7 milliseconds, then we only need another 5 milliseconds to set off the Brake Bag."

The rest is surprisingly simple. Baumann insists it needs nothing special beneath the normal undertray and that even the standard retaining bolts will do the job.

"It's just a piece under the engine. The only thing is to have an underbody which could be bent down to the ground and take the load to decelerate the car," he said.

"The secret is we use the car's braking. The car dives down and the idea is to push the car back to the original position. This leads to an additional dynamic force and increases the friction for a short time."

Engineers are working with a variety of different friction surfaces and even toying with ways to grip the road other than just using friction.

"The main message is that it's not just possible to decelerate by the wheels and tyres. If an impact will occur there are other possibilities and this is a new kind of thinking. This is an idea which leads us to the future."

In Baumann's tests in a C-Class, he compared stops from 70km/h with and without the bag. When they set the Brake Bag off, it was doing 47km/h at the same point the normal car was travelling at 50km/h.

"That does not sound much, but it's the difference between a 50km/h and a 47km/h impact. If you conduct a crash test against this fixed barrier you will have deformed 180mm of the front of the car to get down to 47km/h. The effect is of a much longer front end."

Inflatable side-impact beams
Car companies can manage all kinds of engineering tricks in a frontal crash because they can usually make the first metre or so a crumple zone, designed to sacrifice itself to give the occupants a survivable crash. As crazy as it sounds, the doors of the ESF 2009 include what are effectively inflatable crumple zones -- steel airbags!

Side-on collisions where there is no space for a crumple zone, are what safety engineers fear the most. The obvious fix is to give the side of the car more crumple zone, but that would both shrink interior space and add weight. Governments around the world have long mandated side-impact protection beams, but what Benz is calling Pre-Safe Structure goes even further. In short, it takes the S-Class's side impact beam and turns it into a metal airbag.

While this technology is some way off production, the basics are quite simple. When sensors in the side of the car detect an "unavoidable impact", they trigger an airbag inflator (just like the one in the driver's airbag) inside the beam. Like all airbag generators, this one is a pyrotechnic-powered unit, meaning it's technically an explosive.

When actuated this almost instantly inflates the steel beam to triple its original size -- the pressurised gas itself adds to the strength of the door as well as creating crumple zone.

"When it's not used, it's just folded up to save space and when it's needed we build up the internal pressure to 10 to 20 Bar in a fraction of a second," Schöneburg said.

But it's not just something more to stuff in the door. Benz has an eye on using the technology to strengthen areas like seat mounts and sills – basically any area vulnerable in a side crash.

Surprisingly, the big problem with the metal bags is not weight (Benz in fact calculates Pre-Safe Structure can actually save half a kilogram per door) but rather cost.

"Right now, it has to fulfill all the static requirements and it has to do that now by staying un-deformed, so it's bigger, heavier and more expensive than it needs to be," said Dr Matthias Nohr, Mercedes-Benz's manager of Vehicle Structure Concepts.

"It won't go to production like this. There may be another stage to figure out with a hybrid or aluminium design, but it's all about making the car's body-in-white [the basic vehicle structure] more intelligent.

"But we only have one chance to get this right. It's a real good idea. The good part is that it's not too complicated, but the bad part is that we have to find a solution to make it cost effective," he admitted.

Pre-Safe Pulse
Working on the theory that every millimeter counts in a crash -- especially a side-impact crash -- the Pre-Safe Pulse uses the critical 600 milliseconds 'breathing space' in an accident to inflate air pockets in the seat side bolsters. This pushes occupants around 50mm towards the middle of the car.

Though this doesn't sound much, Schöneburg insists, it is enough to reduce the stresses on the torso in an accident by up to one third.

Again, the core technology isn't new. Some Benz models have had seats with air bolsters for years. The new part is linking them into the heart and soul of the car's communication systems.

Pre-Safe Pulse doesn't just react to the news that there is about to be a crash, though. A development of the new E-Class seat, it has a ‘brain' able to factor in the steering angle, cornering force and car speed to determine how much inflation is required.

A good thing about the Pulse system is that, unlike the Brake Bag or the inflatable intrusion beam, it is reversible and the seat doesn't need replacing.

Belt Bag
The seat belt has saved hundreds of thousands of lives since it was invented and has been improved with three-point mountings, automatic pre-tensioners and belt-force limiters. The Belt Bag adds another dimension to the seat belt.

"A seat belt limits the movement of the torso, but it also subjects the body to considerable forces," Schöneburg explained.

"The belt bag practically doubles the width of the belt to spread the pressure over a wider area -- reducing the risk of injury. This is particularly beneficial for older passengers, whose rib cages are no longer so flexible."

The Belt Bag was developed with Autoliv and has a generator at the edge of the double-layer belt allowing inflation to around four litres. Benz considers that the bag would be most useful in the rear seats, because there is no way to fit frontal airbags there.

"We have children in the rear very often, so we don't want to have an airbag in the [rear of the] front seats for the rear passengers. Also, the front seats move to suit the occupant, then they move again with Pre-Safe," Schöneburg said.

Fully-adaptive Airbags
Airbags were originally one-size-fits-all, which compromised their safety benefits. While there are adaptive airbags on sale now, the ESF 2009's new bags automatically adjust their volume to suit the weight, seating position and stature of the occupant.

The prototype bags have a series of tethers on electric reels. In a crash, the computer tells the bags how much slack to let out with the tethers, so they inflate anywhere from 90 to 150 litres. Normal front airbags inflate to about 120 litres.

Pre-Safe 360°
The Benz Pre-Safe system has traditionally kept an eye on events in front of a car: the ESF 2009 is constantly checking behind and beside itself as well. It scans up to 60 metres behind and applies the brakes if it senses an imminent rear-end collision.

"Contrary to the widely-held opinion, it does not make sense to take one's foot off the brake pedal before an impending rear-end collision," Schöneburg said.

"The correct action is to apply the brakes as hard as possible. However, accident research shows that the driver is moved backwards up to 200mm, which inevitably causes his feet to slip off the pedals.

"So we automatically apply the brakes 600 milliseconds before the collision to prevent the car being pushed into traffic or into pedestrians and to minimise the forward acceleration on the occupants."

Lights tricks
While Mercedes-Benz has only just released its Adaptive High Beam Assist on the E-Class, it is already pushing the technology further.

The existing system was developed with Continental and uses a mechanical rolling screen in concert with infra-red cameras to pull the high-beam light cone gradually back towards the light source and always just ahead of the oncoming car. The new system swaps existing light technology with semiconductor Light Emitting Diodes (LEDs) for the main headlights. These automatically keep the light cone out of the eyes of oncoming drivers.

The ESF 2009's headlights use 100 LEDS each and they can be lit up individually.

It also works with the infra-red camera in a way the current system can't: when the camera picks up a pedestrian or animal in the dark, it repeatedly flashes the lights on the hazard to make sure you see it.

But, as Assistance and Safety Systems senior manager Dr Walter Zeigler explains, it's not without its development issues.

"We will have LEDs as the main lights soon, but the only real problem is cooling them.

"We have to keep the temperature at 120-130 degrees. They have a better efficiency than standard, but they still produce heat and they have to be cooled, even at a standstill, so there'll need to be some sort of coolant."

Child Seat breakthrough
Typical child seats are plastic, but the ESF 2009 uses a new, modular tubular-construction seat developed with restraint-system specialist, Takata.

Suitable for children from three to 12 years, the seat has been designed to restrain the child's head and shoulders, while the height and width can be adapted to suit different children.

"It offers better restraint and more stiffness with side impacts than current systems," Schöneburg insisted.

But the ESF 2009's intelligent communications system is not an exclusively Benz feature. While the company has been working on interactive communication for seven years, it is also working with the rest of the German car industry to come up with a uniform global standard.

"It's very important for compatibility that we have a common standard around the world," Schöneburg told the Carsales Network.

A trial involving 400 vehicles communicating with each other is being conducted in northern Germany currently and will continue until 2012.

"We have different projects worldwide in Japan and the US, and here in Germany. I hope in five years we will have the first cars with this system on the road. And I hope then the rest will follow very fast," Schöneburg opined.