Mercedes-Benz TecDay Real Life Safety - PART VIII


Leipzig, Germany, Nov 12, 2008

PRE-SAFE® Brake: Automatic emergency braking can greatly reduce the severity of a head-to-tail crash

Mercedes-Benz has continued to further develop the PRE-SAFE® Brake, which was first unveiled in 2006. From spring 2009, a version of the system that activates the maximum braking power automatically if there is an acute risk of an unavoidable accident will be available for the new E-Class and the S-Class. The PRE-SAFE® Brake therefore acts as an electronic crumple zone and can greatly reduce the severity of an impact.

Accident research shows that drivers do not always react as quickly as necessary at critical moments – for example because they are distracted and therefore do not recognise the immediate threat of a head-to-tail crash, or because they fail to heed the warning signals given by an assistance system. The PRE-SAFE® Brake intervenes in situations such as these by braking the car automatically.

What's more, it does this in two stages: around 1.6 seconds before the calculated impact point – after three audible warning signals – the system initiates partial braking autonomously and decelerates the car with around 40 percent of the
maximum braking power (approx four m/s²). Designed to supplement the visual and audible warnings, autonomous partial braking gives the driver a further, perceptible signal to act. If the driver then brakes immediately, the maximum braking force is made available or, if the driver swerves, the accident can be avoided at the last moment, depending on the driving situation. Mercedes-Benz first unveiled PRE-SAFE® autonomous partial braking in the CL-Class and the S‑Class in 2006.

Mercedes will be offering a further enhanced version of this safety system from spring 2009. If the driver fails to react, even after automatic partial braking, the PRE-SAFE® Brake activates the maximum braking power around 0.6 seconds before the now unavoidable collision. This emergency braking can greatly reduce the severity of the impact.
The system therefore acts like an "electronic crumple zone", offering the car occupants even greater protection.

Like Brake Assist PLUS, the PRE-SAFE® Brake uses state-of-the-art radar technology to monitor the situation in front of the car and detect an imminent accident. Two short-range radar sensors with a range of 30 metres and a beam width of 80 degrees are located behind the front bumper covering. The additional long-range radar in the radiator grille has a range of 200 metres.

The PRE-SAFE® Brake greatly reduces the severity of accidents

Mercedes-Benz has tested the operation and effectiveness of the PRE-SAFE®
Brake, both on the road and in the road simulator. Around 400 drivers took part in the road tests in Germany and the US, clocking up a total of around one million kilometres in test cars.

Mercedes engineers conducted a series of tests, lasting several weeks and involving 70 drivers, in the road simulator at the Daimler research facility in Berlin. Each of the drivers drove for half an hour and was distracted by an accident on the other side of the road, whilst at the same time the traffic in front of the car braked suddenly. The results of the test, which reflects an everyday situation on the road, highlight the safety-enhancing effect of the sophisticated assistance systems: a total of 70 percent of these test drives remained accident-free thanks to the fast reactions of the drivers and the assistance provided by BAS PLUS and the PRE - SAFE ® Brake. In a third of the simulator tests, those taking part were unable to avoid a crash. In these cases, automatic braking greatly reduced the accident severity.

Realistic tests carried out by the Mercedes engineers have revealed that autonomous PRE-SAFE® emergency braking reduces the impact speed by 16 km/h on average.
The PRE-SAFE® Brake is active at speeds of between 30 and 200 km/h when moving vehicles are detected in front of the car. The system also reacts if the car approaches a stationary queue of traffic, providing its speed is below 70 km/h.

This component is an important part of the PRE-SAFE® anticipatory occupant
protection system, which is fitted as standard in many Mercedes models. It uses the otherwise wasted seconds (from an occupant-safety standpoint) between the point at which a potential accident risk is detected and the point at which the protective systems in the interior are activated.

Just like the airbag, seat-belt tensioner, ESP® and other trailblazing Mercedes
inventions, the PRE-SAFE® Brake was developed based primarily on real accident situations. When used in combination with Brake Assist PLUS, this technology can make a key contribution towards reducing the high number of head-to-tail crashes or reduce the severity of such collisions. In Germany, over 17 percent of all serious road accidents involve head-to-tail crashes. In the US, meanwhile, one in three road accidents involving deaths or injuries are head-to-tail crashes.

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