by Adrian-Liviu Dorofte

Ten years of PRE-SAFE®: the car with protective reflexes celebrates a special anniversary

I. Continuously enhanced and successively introduced in all model series: Ten years of PRE-SAFE®: 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:

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, and is able to prevent accidents with pedestrians at speeds up to 50 km/h. 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.

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

II. Under the microscope: the new sensors. Intelligent networking of eyes and ears

Highly sophisticated sensors and the necessary networked algorithms provide the foundation for innovative new functions. As part of "sensor fusion", DISTRONIC PLUS with Steering Assist, BAS PLUS and the PRE‑SAFE® Brake all employ the same stereo camera and multistage
radar sensors.

Mercedes-Benz is making a major leap forward with the introduction of the Stereo Multi-Purpose Camera (SMPC), or stereo camera for short. Just like the Multi-Purpose Camera (MPC) fitted previously, it is positioned behind the windscreen in the vicinity of the rear-view mirror. It has an aperture angle of 45° and is capable of spatial detection of objects moving crossways ahead and pedestrians, and calculating their path. The camera's two "eyes" provide it with a three-dimensional view of the area up to around 50 metres in front of the vehicle, and it is able to monitor the overall situation ahead for a range of up to 500 metres. In this way, the new camera is able to provide data for processing by various systems.

Intelligent algorithms evaluate this information in order to detect and carry out spatial classification of both vehicles that are driving ahead, oncoming or crossing, as well as pedestrians and a variety of traffic signs within a large field of vision.

Whereas the stereo camera's lenses act as the car's eyes, the radar sensors are its ears, so to speak, and provide additional data. The system of radar sensors comprises two short-range radar sensors in the front bumper with a range of 30 m and a beam angle of 80°, which are complemented by a long-range radar (200 m, 18°) including medium-range detection (60 m, 60°). The data from the camera and radars is amalgamated in a control unit in order to provide the system-specific data for the various functions.

Here is a summary of the sensors and cameras:

- 2 x short-range radars at the front (30 m, 80°)

- 1 x long-range radar at the front (200 m, 18°) with medium-range detection (60 m, 60°)

- 2 x short-range radars on the sides at the rear (30 m, 80°)

- 1 x multi-mode radar at the rear (30 m, 80° and 80 m, 16°)

- Stereo camera (Stereo Multi-Purpose Camera, SMPC) located behind the windscreen in the vicinity of the rear-view mirror (effective range 500 m, incl. 3D capability for approx. 50 m, 45°)

- 12 ultrasonic sensors (4 each at the front/rear + 2 each on the left/right in the front and rear bumpers)

- 4 cameras as part of a 360° camera system (1 each at the front in the radiator grille/behind in the handle recess/below in the exterior mirror housings, vertical angle of approx. 130°, horizontal > 180°, resolution 1 MP (1280 - 800 pixels)

An extensive system of additional sensors is able to keep an eye on the current driving state and the driver's reactions. If the sensors detect a hazardous situation, they are able to feed the algorithms for all manner of assistance systems with data in order to provide just the right support for the specific situation.

III. Development and the future of PRE-SAFE®: PRE-SAFE® was a paradigm shift

Interview with Prof. Dr. Ing. Rodolfo Schöneburg, Head of Passive Safety and Vehicle Functions at Mercedes-Benz Cars

Prof. Dr. Ing. Rodolfo Schöneburg was born on 30 October 1959 in Ciudad Bolivar in Venezuela, studied aerospace engineering and obtained his doctorate at the Technical University of Berlin. He holds an honorary professorship at the College of Technology and Business Economics (HTW) in Dresden. He has been active as the head of the centre for safety/vehicle functions at Mercedes-Benz since April 1999. It was under his aegis that the PRE-SAFE® anticipatory occupant protection system entered series production in 2002, with which Mercedes-Benz started a new era in vehicle safety. Here are some of Prof. Schöneburg's comments on the history and future of PRE-SAFE®.

Professor Schöneburg, preventive safety systems went into series production for the first time in 2002 with the launch of PRE-SAFE® in the S-Class at that time, but how did the history of such systems begin?
Schöneburg: The concept of PRE-SAFE®, namely preventive safety, began as early as the 1990s. How would future safety systems function? Would we always have to wait with our safety systems until an accident actually happened? Or could we activate the systems preventively, i.e. before the accident, when the hazardous situation has been detected? Would it not be possible to improve certain elements in the vehicle in advance, so that subsequently you would be in a better position in the event of an accident? These were the initial ideas. You could compare all of this with human reflexes: in a hazardous situation, you try to hold your hands in front of your head, for example. We wanted to achieve something similar in vehicles.

And at what point did the decisive breakthrough come?
Schöneburg: By the end of the 1990s, Brake Assist and ESP® (Electronic Stability Program) were fitted as standard in all vehicles. As a result, we were now able to detect specific hazardous situations. That is to say, in the event of emergency braking and severe over or understeer, we knew that there was the risk of an accident, and as such we had information at our disposal to enable us to intervene in a preventive way for the first time. The other decisive step was the development of reversible protection systems, in particular the reversible belt tensioner.

Did both of these factors therefore represent a paradigm shift in automotive safety?
Schöneburg: The core element was the consolidation of active and passive safety. Passive safety has always dealt with minimising the consequences of an accident, in particular from the moment at which contact with the other party involved in the accident occurs. Active safety has dealt with driving safety and the avoidance of accidents, as well as maintaining the driving stability of the vehicle. Since the development of PRE-SAFE®, we have moved into a bordering area, the area close to the accident in which we can discuss the probabilities of an accident. The fact that we started to exploit this particular area was a real leap forward; a completely new level of discussion on the topic of safety therefore became possible. How innovative this step was can be seen in the fact that test institutes such as Euro NCAP took years to incorporate preventive safety systems into their analyses. Even other vehicle manufacturers have started to follow our approach in the meantime and also started to integrate preventive protection systems into their models. But that is what distinguishes a true innovation: rather than being just an individual topic it is an issue which significantly influences the development of future systems. Recently aspects of comfort have also started to come into play, because we are providing increasing support to the driver in traffic situations. This networking approach to the "Intelligent Drive" concept had its origins in the development of PRE‑SAFE®.

Initially only a few signals were available when it came to detecting critical situations, such as ESP ® and Brake Assist. How have things moved on in this area today?
Yes, that's right. Figuratively speaking, in the beginning we only "sensed" danger, that is to say we recognised situations involving braking or acceleration. Today the vehicle can also "see". When it comes to sensor systems, a tremendous amount of progress has been made in the past ten years. Today we have a whole host of radar sensors and cameras at our disposal, and we also have information on the behaviour of the driver, such as whether he has his hands on the steering wheel or how quickly he is steering. As a result, we are able to analyse increasingly complex situations and, thanks to improved sensor systems for the surrounding area, we are also able to recognise potential road traffic hazards even better than before. A decisive factor for the new functions has also been the combination of algorithms, which take their data from the enhanced radar sensors and new stereo camera. We call this "sensor fusion". As a result, for the first time the new BAS PLUS Brake Assist system with Cross-Traffic Assist is able to detect crossing traffic and pedestrians. And PRE-SAFE® PLUS can trigger preventive measures in
the event of an impending rear-end collision. Figuratively speaking: the next S‑Class not only has eyes at the front, but also 360-degree all-round vision.

And what is the next step? With the ESF 2009 research vehicle three years ago, you already provided a far-reaching insight into future developments in the field of safety technology.
Schöneburg: Thanks to ever-improving sensor technology, in the coming years we will experience a further paradigm shift. So far it has been the case that have been able to predict an imminent accident with increasing efficiency. But there has always been the option of the collision not occurring, therefore all PRE-SAFE® measures have had to be reversible.

With PRE-SAFE® Impulse, which will celebrate its premiere in the coming year, for the first time we are exceeding this boundary: with this, at an early phase of the crash, before the resulting deceleration starts to increase, the driver and front passenger are pulled against the direction of the impact. This helps to considerably reduce both the risk and severity of injury in a front-end crash. Following in the wake of reliably detecting an accident in this way are further innovative implementation measures. These include some of the ideas presented in the ESF 2009, such as PRE-SAFE® Impulse and PRE-SAFE® Structure.

PRE-SAFE® Impulse is not restricted to a front impact. In the event of a side impact, PRE-SAFE® Impulse is able to reduce the upper body loads on the occupants by around a third, whereby the system preventively moves the occupants by up to 50 mm towards the centre of the vehicle in advance. For this, the anticipatory restraint system uses the air chambers in the side bolsters of the seat backrests. And in the case of PRE-SAFE® Structure, inflatable metal structures save weight or increase the stability of structural components. In an idle state, the metal section is folded away to save space. If its protective effect is called for, a gas generator provides an internal pressure of 10 to 20 bar within fractions of a second, and the section is unfolded to provide significantly more stability.

Innovations are playing an increasingly significant commercial role, and PRE‑SAFE® has made a major contribution to reinforcing the position of Mercedes‑Benz as a safety pioneer. How can you protect this competitive advantage against those wishing to copy your measures?
Schöneburg: Our goal is to maintain our role as a trendsetter in the area of safety. We simply want to prepare the way, and when others follow us along this same route then I think that is a major endorsement of our work. I believe that is what it is all about: if possible making innovations in the field of vehicle safety accessible to others. It is in our interests to increase road safety. And it has traditionally been the case: the inventor Béla Barényi worked for us and registered a great number of patents for the company. He made a major contribution to vehicle safety – he discovered the crumple zone, and developed the impact absorber in the steering wheel. And as a company we have never used any of these patents to block the competition. And, most importantly, after introducing new safety technologies into our luxury class, we also try to introduce them as quickly as possible across our entire vehicle range. As such, the new A and B-Class can equally be regarded as pioneers in the field of safety, with COLLISION PREVENTION ASSIST and PRE-SAFE®.

How does the transfer to the competition work? Are others now developing systems further or are they able to take on your system by acquiring it from you under licence?
Schöneburg: This mainly occurs via the supplier industry. They develop individual systems for us, and then this gives us the opportunity to use them exclusively for a specific period. Or we release a system from the very outset. This normally also helps us, because the numbers then increase and the system therefore becomes more favourably priced.

Credits: Daimler AG

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