Traffic crashes can be seen as one of the world?s largest public health problems. Advanced safety technology can help address this problem effectively.
While automotive mobility continues to be on the rise worldwide, thus promoting economic growth and satisfying the growing demand for individual transportation, the cost of some 1.2 million fatalities each year is certainly not acceptable. Traffic crashes can be viewed as one of the world’s largest public health problems and advanced safety technology can help address this problem effectively.
Accordingly, rating and consumer tests on active and passive safety systems have increasingly gained in importance over the last few years. The aim of these is to provide customers with safety assessments of different vehicles of the same class by using a clear evaluation system. Clearly, manufacturers can no longer afford to ignore the attainment of rating stars as a development objective. The development of suitable structural measures, improvements to the restraint system’s equipment and optimisation of their effectiveness have contributed to enhance accident safety across all vehicle classes. Nowadays, even small vehicles can demonstrate this basic level of safety, but we must mention the fact that the results between different vehicle classes can still not be compared.
The main questions today are: are further improvements to the restraint system, designed to perform better in crash tests, actually sufficient to increase vehicle safety? Or will more requirements from the analysis of real-life accidents have to define what is needed?
For example, it is well known that vehicle speed and impact configuration are key parameters affecting the severity of an accident. But the assessment criteria of New Car Assessment Programs only relate to passive impact protection and therefore, only focus on one limited aspect of how a vehicle might behave in a real traffic incident. However, accident avoidance/mitigation systems, such as anti-lock braking systems, electronic stability programs and brake assist systems have not been taken into account for a long time; even though, these have major – and in the meantime clearly proven - potential for increasing overall safety. Such systems are only now, slowly being included in vehicle safety assessments.
Interactions between the occupant and the vehicle in the pre-crash phase also determine the subsequent severity of injuries sustained. Systems which provide active assistance in this pre-crash phase are still not considered in current ratings, although they can greatly reduce injury severity in real-life accidents.
There is a recognised need for today’s restraint systems to be triggered and activated in a manner that takes greater consideration of the situation, but how should this be implemented in the vehicle? All primary points of contact in the vehicle interior have now been covered and the opening characteristics of frontal systems have been softened. However, we are still seeing that the system configuration is clearly focussed on the crash load scenarios used in ratings and legislation tests.
The primary focus is on severe accidents and in Europe on the 50th percentile occupants. What possible courses of action are available?
Preventive protection systems form the main basis for action. In this respect, the Mercedes-Benz PRE-SAFE® systems offer conventional restraint systems assistance before a possible collision occurs, which means that their optimised effectiveness can also be deployed in real-life situations. An independent investigation conducted by the ADAC has recently proven the effectiveness of PRESAFE®: During a realistic full braking situation, if the occupant is fixed in position by the reversible belt pretensioner and is positioned better by adjusting the seating system, the load experienced by the occupant can be reduced by 30% for the head and up to 40% for the neck when compared with an equivalent situation without PRE-SAFE®.
Figure 1
One of the most important new developments in the field of vehicle safety is the preventive Brake Assist PLUS system. This system registers vehicles ahead by near- and far-range radar sensors (77 and 24 GHz) and gives a warning if the gap is too small or the closing speed is too high. If a collision threatens, Brake Assist PLUS (BAS PLUS) calculates the ideal braking assistance in fractions of a second and makes this available immediately – even if the driver applies too little pressure to the brake pedal. This significantly reduces the incidence of rear-end collisions. The adaptive brake light, which warns following traffic by flashing during emergency braking, also makes a major contribution.
On request, Mercedes-Benz will combine Brake Assist PLUS with the equally unique PRE-SAFE® occupant protection system, which offers even more safety functions. PRESAFE® recognises potential accident situations as they arise: if braking deceleration exceeds a certain level or a skid is imminent, the system tensions the front seat belts as a precaution and inflates air cushions in the multicontour seats to envelop and support the driver, front passenger and rear seat occupants. For the first time, Mercedes-Benz has also integrated the side windows into this preventive protection concept; they are automatically closed when an accident threatens in order to provide maximum support for the window curtain air bags.
This combination of active and passive safety technology (i.e. the new Brake Assist PLUS system and PRE-SAFE®) is a further enhancement to occupant protection offered by Mercedes-Benz. Mercedes-Benz is also the world’s first and only automotive brand with a comprehensive safety system of this kind, which goes into action before an impending accident.
PRE-SAFE® brake even goes one step further. If the driver does not react to the BAS PLUS warnings from the cockpit and there is a severe danger of an accident, the system triggers automatic partial braking and decelerates the S-Class up to 0.4 g. Autonomous partial braking provides the driver with a clear prompt to take action, on top of the visual and audible warnings. If the driver begins to activate the brake, the optimum braking force will be provided by the system, and – depending on the given situation – it may be possible to prevent the accident at the last moment. If this is not possible, the PRE-SAFE® brake reduces the severity of the impact, which in turn reduces the risk of injury for the occupants of the car.
PRE-SAFE® brake is an assistance system, which assists the driver at critical moments. Even during automatic partial braking, the driver retains responsibility for the vehicle and decisive action on his or her part can help prevent the vehicle from colliding with the car in front.
PRE-SAFE® brake is the first system to be introduced worldwide which is designed to reduce the severity of accidents and injury. The combination of visual and audible warnings and autonomous partial brake application, in conjunction with activation of reversible occupant protective measures, improves the situation for everyone involved in an accident. It is supplemented by the BAS PLUS Brake Assist, which provides optimum controlled deceleration in a critical situation based on information of radar sensors.
PRE-SAFE® brake avoids or reduces the severity of a large number of accident situations encountered when travelling in the same direction as the flow of traffic. However, in the future, there will be situations which happen spontaneously where there is no time for the system to issue a warning or sensor-based limitations do not allow it to trigger automatically. New communication technologies can bridge these gaps or improve the situation in case of unavoidable collisions.
Figure 2
In addition to adapting systems to the traffic situation, the adaptation to the individual occupant is also gaining in importance. Increasingly, this involves the consideration of individual facts about the occupant such as belt-wearing status, occupant proportions, and seating position.
The design of today’s restraint systems is designed around the 50th percentile occupant. Adapting the restraint systems through the absorption ability of the belt force, inner airbag pressure, steering column force, and airbag ignition time further extends the usable spectrum. The goal is to take into account the individual parameters available. Reducing the sensors’ input parameters and actuators’ effectiveness parameters is important to technical controllability. Initial internal investigations have shown that limiting the settings to low and high in the system opens up adaptation options for attaining the following goals:
New possibilities for the enhancement of active and passive safety are also opening up through the exchange of information (Car2Car; Car2Infrastructure): Vehicle communication technologies can be used both for warning systems (accident avoidance) as well as for applications in the actual collision zone. In the actual collision zone, relative speed, collision trajectory and physical parameters of the colliding objects are relevant in determining the severity of an accident. Weight, rigidity, and geometry of the structures affected are of prime importance here. Knowledge of the aforementioned parameters would therefore reduce the severity of particular accidents, if we assume that they can no longer be avoided. Complete coverage of accident escalation, including the field of unavoidable collisions, with vehicle communication technologies is therefore needed.
Figure 3
One single solution to avoiding accidents will not solve the issue in all circumstances, because our traffic environment is far too complex for that. Yet supplements to and the joint action of active and passive safety, especially in the transitional area between the two disciplines, is the key to improving the effectiveness of today’s safety systems.
Keywords: Automotive Safety, Safety Technology, Adaptive Safety Systems, Restraint Systems, Mercedes-Benz PRE-SAFE®, Preventive Brake Assist (PLUS), PRESAFE®,
