Innovations: safety development based on accident research

Oct 28, 2019
Stuttgart

Accident research plays a major role in protecting the technological lead of Mercedes-Benz. The reason being that the knowledge from the real world does not remain theory for long. All road users benefit from accident research: numerous Mercedes-Benz safety innovations such as the window airbag or PRE-SAFE® were developed on the basis of the accident research findings. Some examples.

Design of the interior: In the late 1960s, when Mercedes-Benz began analysing accidents systematically, the attention of the experts was mainly on the crash protection in the interior. Although seat belts were already available for the saloon cars from Mercedes-Benz, they were still used very little. The consequences were serious head injuries sustained by many front passengers when they impacted the steering wheel, dashboard or windscreen. That is why the accident researchers started to look for the particularly dangerous contact areas in the interior and then made suggestions for the redesign of switches, handles and levers. From then on, the materials for the dashboard and interior trim panels were also selected from the aspect of accident protection. Automotive engineers have preferred energy-absorbing materials ever since.

Body shell structure: After "defusing" the interior, the work of the accident researchers and safety engineers focused on further improving the body shell structure. When reconstructing typical collisions with oncoming traffic, the accident researchers had realised that the vehicles most often collided asymmetrically and that the front sections of the body shell were consequently subject to a one-sided load. The experts refer to this type of accident as an off-set impact. These insights had consequences for automotive engineering. Because the legally mandated frontal crash with full overlap against a flat wall as a safety test for passenger cars represented only part of the real accidents, Mercedes-Benz pursued its own strategy. Based on the accident research data, the engineers conducted initial crash tests based on the off-set principle as early as 1974 and in the forked front member realised a design principle for their passenger cars that offered very good occupant protection even under extreme loads on part of the vehicle's front-end assembly. The S-Class (model series W 126) presented in 1979 was the first model whose crash structure was based on the principle of the forked front member and was designed specifically for the off-set head-on collision.

Test procedures: Years later, the continuous observation of accidents revealed that a further modification of the test procedure was required. Based on this, Mercedes-Benz developed the off-set crash against a deformable barrier: an aluminium structure simulates the crumple zone of the other vehicle involved in the accident during the crash test and in this way makes it possible to conduct a more realistic analysis of the deformation behaviour of the body shell than an impact against a rigid concrete or steel barrier. Today, all newly developed passenger cars in Europe are subject to the crash against a deformable barrier co-developed by Mercedes-Benz. It is rooted in the law and is also part of the Euro NCAP test programme (New Car Assessment Programme).

Seat belts: Experiences from real-life accidents shaped the development of pioneering safety details in the 1970s and 1980s. Most notably the three-point seat belt, which Mercedes-Benz offered its customers for the first time in 1968. However, accident research showed the engineers that good things can still be further improved in this case as well. That was realised with an improved belt geometry, for example.

Airbag: After 13 years of development and testing, the airbag found its way into series production in late 1980. In 1998, Mercedes-Benz demonstrated that the airbag functions can be tailored even more specifically to the severity of the particular accident when it presented the new S-Class (model series W 220). The engineers had developed an innovative, two-stage gas generator capable of inflating the airbag depending on the severity of the impact. Mercedes-Benz had designed the airbag as a supplement to the three-point belt from the start. The results of the accident research showed the veracity of this principle: while some 30 percent of the belted drivers of Mercedes-Benz passenger cars suffered life-threatening injuries in very severe head-on collisions in the 1970s, today the accident researchers register only isolated accidents in which someone suffers injuries of this very great severity thanks to the coordinated interaction of belt, belt tensioner, belt force limiter, airbag and other protective measures. Most of the time these involve extremely severe accidents, however.

Belt force limiter: In the mid-90s, accident research showed that the use of belt tensioners and airbags for driver and front passenger as standard made a new overall set-up of the restraint system possible. As a result, Mercedes-Benz integrated the belt force limiter, which systematically limited the restraint effect of the belt. In combination with the airbags, this enabled significantly lower loads on the chest of the front passengers and thereby mitigated the consequences of an accident.

Side airbag and window airbags: The many years of Mercedes-Benz commitment in matters of occupant protection had a broad impact. The accident researchers were able to report positive news as early as the start of 1998: in the past two decades, the risk of extremely serious to fatal injuries in a severe head-on collision had been reduced significantly. Fatal injuries of belted car occupants occurred almost exclusively in extremely severe head-on crashes. As a result, the side-on impact became the focus of the safety developers. The percentage of such collisions in accidents with severely injured vehicle occupants had been changing continuously since the 1990s. While it was still 14 percent in 1985, that number had already risen to 30 percent in 1995. Mainly evident was the increasing influence of side-on collisions in traffic accidents involving car occupants suffering fatal injuries.

Consequently, the safety researchers put together a package of protective measures, which in addition to stable door locks and door hinges also included special deformation elements and foam pads in the interior panels of the doors. Furthermore, Mercedes-Benz passenger cars have side protection reinforcements in the lower section of the doors. This creates an effective side impact protection, which was further improved with the use of side airbags in 1995 and window airbags in 1998.

The development of the window airbag was based on the in-depth investigations of Mercedes-Benz Accident Research. They showed that severe head injuries were possible in a side-on crash. The large air cushion, which is activated together with the side airbags in a side-on collision with accordingly great impact severity and unfolds like a curtain in front of the side windows, is able to soften a potential impact of the head against the side window or even penetrating objects.

PRE-SAFE®: The accident researchers realised that more than two thirds of all accidents are preceded by critical driving situations such as skidding, emergency braking or sudden evasive manoeuvres, which already allow conclusions to be drawn about an impending collision. This valuable time before the crash remained unexploited for a long time. Since 2002, the answer has been PRE-SAFE®. This anticipatory occupant protection system is able to detect an impending accident beforehand and springs into action to prepare the occupants and the car for a potential collision, for example, by using electric motors to tension the seat belts as a precautionary and reversible measure. As a result, the phase before the possible impact is put to the best possible use for deploying preventive safety measures.

Flashing brake lights: Accident research showed that three quarters of all severe traffic accidents could be prevented if motorists were warned of dangers at an early stage. That is why Mercedes-Benz developed the Adaptive Brake Lights system. It can help greatly in preventing rear-end collisions. The reason being that studies show that the braking reaction time of motorists can be shortened by up to 0.2 seconds on average if a flashing red warning light is used instead of a conventional brake light in emergency braking situations - valuable time to give motorists more room to stop.

DISTRONIC PLUS and Brake Assist PLUS: The Mercedes-Benz assistance systems DISTRONIC PLUS (current name: Active Distance Assist DISTRONIC) and Brake Assist PLUS (see also Active Brake Assist below) based on modern radar technology make an effective contribution to accident prevention. This was the result of an analysis conducted by Mercedes-Benz in 2008 based on representative accident research data. This technology can prevent one fifth of all rear-end collisions on average in Germany alone. On motorways, the accident rate can even be reduced by about 36 percent.

Lower injury risk: Mercedes-Benz drivers travel the roads more safely than drivers of other brands. That was the finding of an accident research investigation in 2009 based on official anonymised data of the Federal Statistical Office of Germany. The investigation looked at 18,748 accidents involving personal injuries in the period from 2003 to 2007. According to it, the risk of suffering serious or fatal injuries driving an E-Class is 10.4 percent lower than in vehicles of comparable other brands.

Active Brake Assist: In a study conducted in autumn 2014, the accident researchers of Mercedes-Benz came to the conclusion that up to 20 percent of all serious rear-end collisions in Germany could be prevented if all vehicles were fitted with an equivalent safety system such as the radar-based COLLISION PREVENTION ASSIST distance warning system. For the further advanced successor system, COLLISION PREVENTION ASSIST PLUS, the accident researchers were even forecasting up to 30 percent fewer severe rear-end collisions than without the system. They based their claim on a simulation study using the "pre-crash matrix", a digital accident database from the Traffic Accident Research Institute in Dresden containing thousands of painstakingly reconstructed real-life accidents. As part of this study, vehicles were equipped virtually with this predecessor system of Active Brake Assist and the effects on each individual rear-end collision were examined. Mercedes-Benz launched COLLISION PREVENTION ASSIST as standard in 2011 in the previous generation of the B‑Class.

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