When Mercedes-Benz first introduced PRE-SAFE in 2002, it was described as a system which could ‘predict’ an impending accident and initiate measures to reduce the severity of the impact on the occupants of the vehicle. There are no statistics to show how many lives PRE-SAFE has helped to save, or how many injuries it has helped to prevent or minimise. However, analyses carried out by Mercedes-Benz accident research teams have shown that more than two-thirds of all traffic accidents are preceded by critical driving situations which enable conclusions to be drawn about risks or impending collisions. PRE-SAFE is therefore a significant element of the holistic safety concept of Mercedes-Benz known as “Real Life Safety”.
Analyses performed during crash tests show just how important and effective anticipatory occupant protection can be. In the case of seatbelt tensioning, for example, the precautionary measures mean that the driver and front passenger are held in their seats in the best possible position and so do not move forwards as much prior to the impact as a result of emergency braking, and the loads exerted are therefore reduced. These tests have shown that the head of a dummy is subjected to around 30% less stress, while a reduction of around 40% has been recorded in the neck area.
“The essential feature of PRE-SAFE is the way in which it links the phase prior to the accident with the phase during the accident”, explained Prof. Dr. Rodolfo Schoneburg, Head of Passive Safety and Vehicle Functions at Mercedes-Benz Cars.
“In the past, it was the case that passive safety systems were not activated until the moment of the accident. That was the point at which the airbags were inflated, the seat belts tensioned, etc. Prior to this, active safety systems such as Brake Assist and ESP were engaged. With PRE‑SAFE, for the first time, we have used the active safety systems to condition or activate the passive safety systems,” he said.
PRE-SAFE is able to activate protective measures for the vehicle’s occupants as a precaution. The aim is to prepare the occupants and vehicle for an imminent collision so that the seatbelts and airbags are able to fulfil their protective function to maximum effect during an impact. What’s more, the PRE-SAFE protective measures are reversible: if the accident is averted, the advance tensioning of the seat belts is halted automatically and the occupants are able to reset the positions of the seats and the sliding sunroof. The anticipatory occupant protection system is then immediately ready for action again.
PRE-SAFE can be activated in the event of emergency or panic braking, severe oversteer or understeer, critical steering manoeuvres or increased brake assistance by the adaptive Brake Assist system. Early detection of an accident is possible because PRE-SAFE is networked with the Brake Assist and ESP systems. Their sensors detect potential critical driving situations and send appropriate information to the electronic control units within milliseconds.
When installed in combination with DISTRONIC PLUS, PRE-SAFE also uses the information provided by the short-range radar sensors in the front bumper to tension the front seatbelts at the very last moment before an unavoidable collision, thus reducing the forces exerted on the driver and front passenger during a crash. This PRE-SAFE function is literally the “ultima ratio” of anticipatory occupant protection, since the accident occurs around 150 milliseconds later.
A book on biology served as a source of inspiration; images of a cat among documents belonging to his daughter who was studying prompted Mercedes-Benz engineer Karl-Heinz Baumann to come up with the idea of an anticipatory occupant protection system. This is because a cat turns and stretches itself when falling, to ensure that it is in the best possible position prior to landing.
In 1999, Mercedes-Benz established a PRE-SAFE steering committee comprising employees from the two areas of active safety – i.e. accident avoidance – and passive safety. “We met on a regular basis, and on the one hand developed the sensor system and trigger algorithms, and on the other the actuators in the vehicle, such as a reversible seat belt tensioner in particular”, recalled Prof. Schoneburg. “The main innovation was this novel linking together of active and passive safety.”
“The name PRE-SAFE comes from ‘preventive occupant protection’, or ‘preventive safety'”, explained Mr. Baumann. “That was the key idea: to use the time to undertake preventive, reversible measures which, if an accident were to occur, would be an advantage, but which if an accident were not to occur, would not be a disadvantage.”
Mercedes-Benz launched the first generation of PRE-SAFE in the S-Class as standard as early as October 2002.
In the next generation of the S-Class, Mercedes-Benz is extending the PRE‑SAFE system even further with a number of new functions. These can help to prevent collisions with pedestrians and vehicles in front in city traffic.
PRE-SAFE is now available in a total of 14 model series in the Mercedes-Benz range and almost 60% of its passenger cars delivered worldwide in 2012 have been fitted with the system.
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