The car with protective reflexes celebrates a special anniversary
Ten years after the PRE-SAFE® anticipatory occupant protection system celebrated its world premiere in the S-Class (W 220) in the autumn of 2002, PRE-SAFE® is now available in a total of 14 model series right across the Mercedes-Benz Cars model range, from the A-Class to the S-Class, and is currently able to trigger anticipatory measures in up to eleven hazardous scenarios. Almost 60 percent of Mercedes-Benz passenger cars delivered worldwide in 2012 have been fitted with PRE‑SAFE®. And in the next S-Class, Mercedes-Benz is once again extending the PRE-SAFE® system with the addition of a number of new functions.
There are no statistics to show how many lives PRE-SAFE® has helped to save in the meantime, or how many injuries it has helped to prevent or minimise. However, analyses carried out by Mercedes-Benz accident research 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 seat belt 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 percent less stress, while the Mercedes-Benz engineers have recorded a reduction of around 40 percent 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”, explains Prof. Dr. Rodolfo Schöneburg, 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.”
Ten years after its introduction in the autumn of 2002, PRE-SAFE® is now available in a total of 14 model series. In 2012, almost 60 percent of all of the Mercedes-Benz passenger cars delivered worldwide have been fitted with PRE‑SAFE®. The rapid spread of PRE-SAFE® as well as radar-based driver assistance systems right across all model series at Mercedes-Benz is also reflected in the number of installed sensors: some 50,000 radar sensors were installed in the vehicles delivered in October 2012. Prior to the introduction of COLLISION PREVENTION ASSIST as standard in the new A and B-Class, this number was significantly lower – the 10,000 mark was surpassed for the first time in April 2011. In total, precisely 756,352 radar sensors have been installed in the Mercedes-Benz vehicles delivered to date.
Triggering anticipatory measures in mere milliseconds: how it works
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 seat belts 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® is activated for example in the event of emergency or panic braking, severe over 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.
PRE-SAFE® triggers the following anticipatory measures:
|PRE-SAFE® in situations withcritical longitudinal dynamics||PRE-SAFE® in situations with critical lateral dynamics**|
|Driver and front-passenger seat belts are tensioned.||The side windows are closed, leaving only a small gap.|
|The seat fore-and-aft and height adjustment, and the cushion and backrest angles of the front passenger seat* are moved to the best possible positions for crash conditions.||The sliding sunroof* is closed, leaving only a small gap.|
|Bolsters in the seat cushions and backrests of the multicontour front seats* are inflated.|
*if fitted in the particular vehicle **in addition to the emergency-braking measures
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 seat belts 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.
Learning from the reflexes of a cat: development
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,” recalls Prof. Schöneburg. “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,'” explains Karl-Heinz 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.”
PRE-SAFE® has been tested extensively in Mercedes-Benz vehicles. An important principle applied here: the new systems were not to restrict the freedom of the driver to make decisions, nor compromise the driveability of the vehicle. Acceptance tests in the driving simulator and out on the road have also shown that the PRE-SAFE® systems appear to enhance the subjective sense of safety of the passengers. This is because of the good position maintained in the vehicle. Another lesson learned was that the test subjects reacted quicker in respective hazardous situations.
Mercedes-Benz launched the first generation of PRE-SAFE® in the S-Class as standard as early as October 2002. At that time the scope of its features was as follows: if the car detected a critical driving situation with the aid of the ESP® sensor system, the seat belts of the driver and front passenger were tensioned as a precaution, the electric front passenger seat (optional extra) was moved into a better position from an accident standpoint, and the sliding sunroof was automatically closed.
In 2005, Mercedes-Benz combined PRE-SAFE® with Brake Assist PLUS: when the necessary assistance from the Brake Assist system exceeds a specific level, PRE-SAFE® is enabled. In addition, PRE-SAFE® safety functions were extended: for the first time Mercedes-Benz also incorporated the side windows into the preventive protection concept; prior to an impending accident, they are automatically closed. If the vehicle is fitted with active multicontour seats (optional extra) and the PRE-SAFE® control unit detects a critical driving situation, it immediately activates the air cushions in the seat cushions and backrests. They embrace the vehicle occupants and support them. As a result, the driver and front passenger can be positioned even better and whiplash movements of the upper body – which often occur immediately before an accident when vehicles get into a spin – limited at the same time.
Mercedes-Benz set a further milestone in vehicle safety in 2006 with the PRE‑SAFE® Brake. It enables Mercedes-Benz passenger cars to be braked autonomously in an impending rear-end collision.
Since 2009, a further stage of development of this safety system has been implemented, depending on the vehicle model: if the driver fails to react even after automatic partial braking, the radar-based PRE-SAFE® Brake activates the maximum braking pressure around 0.6 seconds before what is now recognised as an unavoidable collision – an emergency braking action that can significantly mitigate the severity of the impact.
Since the launch of the new B-Class in 2011, PRE-SAFE® has also been available in the compact class for the first time.
Now with pedestrian detection: new functions
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, defuse dangerous situations caused by traffic behind and enhance the protection offered by the seat belts. The following is an overview of the new PRE-SAFE® functions:
BAS PLUS and PRE-SAFE® Brake: besides the addition of pedestrian detection, autonomous braking as a result of vehicles in front has undergone a major enhancement, too. By “fusing together” the data from the stereo camera and radar sensors, it is now possible to detect pedestrians in front of the vehicle. Visual and acoustic warnings are given when a hazard is spotted. If the driver then reacts by braking, the braking power will be boosted by BAS PLUS as the situation requires, right up to full brake application. Should the driver fail to react, the PRE-SAFE® Brake will trigger autonomous vehicle braking. The PRE-SAFE® Brake with pedestrian detection is active up to 72 km/h (45 mph), and is able to prevent accidents with pedestrians at speeds up to 50 km/h (31 mph). The operating range of the autonomous braking function for stationary vehicles has been optimised so that rear-end collisions can likewise now be avoided at speeds of up to 50 km/h (31 mph).
PRE-SAFE® PLUS: PRE-SAFE® PLUS offers an extension of the occupant protection measures in situations where traffic behind poses a danger. A radar sensor in the rear bumper monitors the traffic behind the vehicle and can detect the risk of a rear-end collision. The system warns the driver of the vehicle behind by activating the rear hazard warning lights at a higher frequency than normal. Apart from this, the PRE-SAFE® anticipatory occupant protection measures, including the reversible belt tensioners, are also deployed. If the vehicle is stationary, PRE-SAFE® PLUS will keep it firmly braked. The reduction in the forward jolt which can be achieved in this way can also greatly reduce the load placed on the occupants, such as the risk of whiplash injuries. Firmly applying the vehicle’s brakes can help to prevent secondary accidents too (such as running into a vehicle in front, for example, or colliding with pedestrians or other road users at junctions) or at last reduce their severity.
PRE-SAFE® Impulse: at an early phase of the crash, before the resulting deceleration starts to increase, the front occupants are pulled against the direction of impact – i.e. subjected to momentum – and pulled deeper into their seats by their seat belts. By the time the accident enters the phase when loads peak, the extra distance they are retracted by can be used while dissipating energy in a controlled fashion. Pre-acceleration and force limitation allow the occupants to be temporarily isolated from the effects of the crash, significantly reducing the risk and severity of injuries in a frontal collision. With PRE‑SAFE® Impulse, the seat belt is retracted by pyrotechnic means at all three belt anchorage points, and released again with controlled force. The fundamental difference compared with conventional belt tensioners is that the force for retracting the belt strap is maintained for a much longer time. The deployment logic fires the seat belt system’s belt tensioners progressively depending on the seriousness of the accident. In this way, the tensioning force can be adapted as required.
PRE-SAFE® Rear: with the active seat-belt buckle, an electric motor extends and retracts the belt buckle automatically. In this way, any belt slack in the area of the pelvis and thorax can be reduced so that passengers are secured more firmly in both the sideways and the lengthways direction. Fastening seat belts in the rear has also been made simpler: the seat belt buckle emerges from the upholstery when the rear doors are opened and is provided with an illuminated insertion slot.
In keeping with Mercedes-Benz’s integral safety concept, the active seat-belt buckle covers all four areas of automotive safety – “Safe driving,” “In the event of danger,” “In an accident” and “After an accident.” Details of the functions are as follows:
- seat belt extender function and easier belt fastening
- seat belt adjustment/reduction of belt slack after fastening
- PRE-SAFE® belt tensioner
- post-safe function (seat belt extends upwards after an accident,thereby facilitating access for rescue personnel)
Multiple honours: the most important awards
Mercedes-Benz has received numerous awards and prizes throughout the world for its PRE-SAFE® anticipatory occupant protection system. The following is an overview of the most important awards:
- February 2003: “Paul Pietsch Prize” from the editorial team of”auto motor und sport,” Stuttgart
- March 2003: “Europa Auto 1” Innovation Award, editorial team of “AutoBild,” Geneva Motor Show
- April 2003: “Auto der Vernunft” (Most Sensible Car) – Innovation Award, “Guter Rat” consumer magazine, Leipzig Auto Show
- April 2003: Traffic Safety Achievement Award – Category Manufacturer, World Traffic Safety Symposium, New York International Auto Show
- May 2003: U.S. Government Award for Safety Engineering Excellence for Mercedes-Benz safety engineer Karl-Heinz Baumann, the “spiritual father” of the PRE-SAFE® system
- September 2003: “Auto & Electronics” Award, International Commercial Vehicle Show, Frankfurt
- November 2003: nomination for the “Future Prize” of the German Federal President, Berlin
- December 2004: Prince Michael Award for International Road Safety, London
- October 2010: Euro NCAP Advanced Award for the PRE-SAFE® occupant protection system and the PRE-SAFE® Brake assistance system in the E-Class
- November 2011: Euro NCAP Advanced Award for the PRE-SAFE® occupant protection system and the PRE-SAFE® Brake assistance system in the B-Class, C-Class, M-Class and GLK-Class