Occupant Protection - Safety from Experience: From the Crash Crumple Zone to the Safety Network

Jun 15, 2007
  • The development of safety in passenger cars began in Sindelfingen, 68 years ago
  • Further progress thanks to the networking of active and passive safety
  • PRE-SAFE® with anticipatory crash analysis in the future
  • “Made-to-measure” safety according to height and seat position
Although automobile developers were already thinking about continually improving the driving safety of their vehicles more than 100 years ago, occupant protection itself is a relatively young development discipline. Its story really began on August 1, 1939. Like many other big stories, it started off small - in a wooden shed on the outskirts of the Mercedes plant in Sindelfingen. Measuring nine by 12 meters, the shed housed the workshop of Béla Barényi, a young, talented, impatient engineer whose stated aim was to revolutionize automotive technology. “The axles, body shell, frame and steering of the cars of the future will all have to be different from today’s,” he explained to Wilhelm Haspel, then Chairman of the Board at Daimler-Benz, at the job interview.
In Sindelfingen, Barényi was given the opportunity to bring about the required improvements. The “platform frame for motor vehicles” was his first invention for his new employers. It improved side-impact protection and offered a solid basis for a “rigid passenger cell”. The new design was patented in February 1941. By that point, however, Barényi’s ideas had already moved on. His vision was of a robust occupant cell “surrounded by crash crumple zones front and rear.” It sounds simple, but actually requires a great deal of engineering design know-how. Barényi approached his objective with a series of project studies. In 1952, the vision gave rise to a patent. What’s more, it established a fundamental principle that still forms the basis of passive safety technology today. After successful crash tests, the invention - the crash crumple zone - went into series production for the first time, in the Mercedes models 220, 220 S and 220 SE of the W 111 production series. The year was 1959.
Béla Barényi was the first safety engineer at Mercedes-Benz - in fact possibly the first anywhere. Dozens of engineers have followed in his footsteps, all of them recognizing, as Barényi did, the need to improve road safety. The Mercedes plant in Sindelfingen was, and still is, the nucleus of all of the pioneering work in this field. It was here on September 10, 1959 that the illustrious car manufacturer began systematic safety testing - testing which revealed a need for further safety systems.
Such whole-vehicle crash tests were a pioneering introduction back then. Cables and steam rockets were used to accelerate the test cars. For the rollover test the technicians designed a “corkscrew ramp” and, in the absence of test-dummies, some engineers carried out the tests themselves. Later mannequins were used, followed in 1968 by the first dummies.
Three dozen crash tests for a safety star
Safety development at Mercedes-Benz is still based on crash tests. Approximately 500 impact tests are carried out every year at the Development Center in Sindelfingen - in addition to the roughly 50,000 realistic computer-simulated crash tests carried out in a year. The new C-Class, for example, has passed not only more than 100 crash tests conducted under everyday driving conditions, but also a further 5,500 or so crash tests in the computer. The test program included all the impact configurations currently required for the worldwide registration of a new car:
  • The European Union stipulates the frontal impact test at 56 km/h and the side impact at 50 km/h. Mercedes-Benz also tests in accordance with the three Euro NCAP crash configurations: the frontal impact test at 64 km/h, the side impact test at 50 km/h and the side impact pole test at 29 km/h.
  • Mercedes passenger cars intended for sale not only in , but in all parts of the globe, have to pass a much wider range of tests. Worldwide registration currently requires two dozen impact configurations.
  • Mercedes-Benz also tests the safety of its passenger cars in nine demanding in-house crash tests, some with requirements markedly exceeding the standards specified by law. These include the rollover and roof-drop tests plus special frontal, side and rear crash tests. Passing these tests is crucial if a vehicle is to earn the highest rating in car safety: the Mercedes star.
Today’s new Mercedes passenger cars have to pass a total of more than three dozen different crash tests.
Four phases of safety
Béla Barényi’s commitment and inventive talent are still very much in evidence at the today. Every day, hundreds of engineers deliberate how they can make car travel even safer, and everyday driving conditions and situations continue to be the measure of all things. The development of future assistance and protection systems is not determined by statutory regulations and rating requirements alone, but also by a broad spectrum of real accident data. In other words, it involves all aspects of driving - and takes into account everything that affects the safety of occupants and other road users. The current Mercedes safety concept divides this range of responsibilities into four phases:
1. Safe driving:
Avoid dangers, warn and assist in good time
2. In the event of danger:
Act preemptively with PRE-SAFE®
3. In an accident:
Provide appropriate protection
4. Following the accident:
Avoid more serious follow-up incidents, provide rapid assistance
Crash crumple zones on multiple levels
Mercedes engineers today continue to use accident research, crash tests and modern analyses to enhance Béla Barényi’s crumple-zone principle. In today’s Mercedes passenger cars the impact protection is based on a multi-stage concept that is activated fully or partially according to the severity of the accident. The new C-Class, for example, features four independent impact planes - which means that forces can be dispersed over a large area of the body and diverted away from the passenger cell.
In addition to the robust aluminum cross member at the front and the longitudinal members with their long forward extension - which divert the forces into the side structure, the bulkhead and the transmission tunnel - the high-strength steel integral support frame is also used for the first time as a load plane.
In an offset frontal collision, the side skirts, which have been extended forward, brace the wheel and prevent it from penetrating the footwell. This also allows additional absorption of energy via the wheels. To ensure the required bracing and location of the front wheels, Mercedes-Benz also developed special struts and additional impact elements inside the wheel arches. The struts are arranged diagonally and prevent the passenger cell from lowering in an impact.
Mercedes-Benz has also continued to develop the steering. It is fitted with an energy-absorbing element, which means the steering column telescopes by up to 100 millimeters in the event of a frontal impact. This allows the driver a greater deceleration path.
Occupant cell as hard core
While the various support structures at the front, sides and rear are designed to deform strategically on impact and absorb energy, the passenger cell is the “hard core” of the C-Class safety concept. Even in a severe accident it deforms only slightly, and the protected occupant area is preserved.
The Mercedes engineers achieved this by making more intensive use of very high-grade and ultra high-grade steel with graduated wall thickness, and by developing an extremely robust floor assembly. This consists of two continuous longitudinal members, several cross members and two transmission tunnel braces, which can transmit the impact forces to the unaffected side of the vehicle during a side impact.
Around 70 percent of all the C-Class bodyshell panels are made from these grades of steel - a new peak value in car development. Other noteworthy factors include the cutting-edge, ultra high-strength steel panels which have been developed in recent years. They offer three to four times the tensile strength of conventional high-grade steels and are therefore indispensable when it comes to fulfilling stringent Mercedes requirements for safety and lightweight engineering. These ultra high-strength high-tech alloys make up around 20 percent of the weight of the new C-Class bodyshell.
A new era of passenger car safety
Crash crumple zones, airbags, seat-belt tensioners, sidebags, belt force limiters, windowbags and other technical milestones from almost seven decades of intensive and successful safety development at Mercedes-Benz would seem to have largely exhausted the potential for further improving passive safety. New concepts are needed if the level of occupant protection is to be further increased. And Mercedes-Benz has developed such concepts, launching a new era in vehicle safety with PRE-SAFE® in the year 2002. What’s new is that this system reacts to critical driving situations and prepares the vehicle and its occupants for a possible accident.
When designing the anticipatory occupant protection, the Mercedes engineers distinguished between critical driving maneuvers involving high lateral or extreme longitudinal dynamics. Depending on the situation, precisely differentiated preventive measures are activated - always with the aim of ensuring that tried-and-trusted safety systems such as seatbelts and airbags can offer maximum protection in the event of a collision:
  • In the event of emergency or panic braking using Brake Assist, PRE-SAFE® tightens driver’s and front passenger’s seat belts in advance as a precaution to press them firmly into their seats, increase the distance to the dashboard and reduce the forward movement of front seat occupants in the event of an accident. To provide this important PRE-SAFE® function, the front belt tensioners in the sedans are fitted with powerful electric motors that respond within milliseconds to take up the belt slack.

    In the event of emergency or panic braking, PRE-SAFE® also starts moving the front passenger seat into a better position as a precaution if the current settings are not ideal - provided an electrically adjustable front passenger seat with memory function is fitted. The system adjusts the angle of the front passenger seat cushion and backrest as well as the seat’s longitudinal setting. The system moves the front passenger into a position that enables the airbag to deploy more effectively and provides firm restraint by means of the shoulder strap. The risk of sliding forward under the seat belt and being injured in the event of an accident is also reduced.
  • In the event of skidding caused by heavy understeer or oversteer, PRE‑SAFE® activates additional safety functions: The sunroof and side windows start to close as a precaution if the car starts to skid, and closed side windows provide better support for the windowbags that inflate in the event of a side impact or rollover. This preventive measure also reduces the risk of occupants being thrown from the vehicle or objects flying into the car from outside.

    The sunroof is also networked with PRE-SAFE® because accident researchers frequently find that occupants are thrown out of the vehicle through the open roof when the vehicle rolls over. Closing the sunroof as a precaution also reduces the risk of objects flying into the car from outside.
Analysis of data from crash tests carried out by Mercedes engineers shows just how important and effective anticipatory occupant protection is. Take belt tensioning for example: Because the driver and front passenger are optimally secured in their seats thanks to this precautionary measure and do not move as far forward on impact, the loads on the head and neck are reduced. The loads on the head were around 30 percent less during these tests, and the experts in Sindelfingen found the loads on the neck were even reduced by about 40 percent.
All precautionary PRE-SAFE® measures are reversible: If the accident is avoided, the preventive tensioning of the seatbelts is automatically deactivated and the occupants can return the seats and the sunroof to their original positions. The preventive occupant protection is once again ready for operation immediately after every precautionary activation.
Mercedes-Benz views PRE-SAFE® as the logical and consistent continuation of its long-term philosophy of passenger car safety for everyday driving conditions. Based on the accumulated knowledge of the company’s in-house accident researchers, PRE-SAFE® bridges the gap between active and passive safety - one of the most important preconditions for further advances in the area of automotive safety.
PRE-SAFE® also with anticipatory crash analysis in the future
Mercedes-Benz will further extend the PRE-SAFE® concept in the future, and thus make full use of the phase prior to an immanent accident to activate preventative protection measures for occupants.
The safety engineers from Sindelfingen hope that in the future they will be able to detect in advance precisely what type of accident is about to occur. Which direction will the impact come from? At what speed will the vehicles collide? This and other data can be gathered using cutting-edge radar sensor technology, available in the CL-Class and S-Class. Electronic object recognition is another possibility for the future, establishing the scale of approaching vehicles and their weight using stored empirical values. This enables the system to “see,” for example, whether the vehicle approaching on a collision course is a truck, a bus or a car, allowing it to calculate the severity of the impending impact.
Before an accident, every fraction of a second counts when it comes to preparing car occupants appropriately for an imminent impact. Pre-emptive crash analysis is therefore a crucial step towards enhancing occupant safety - and an important supplement to the familiar PRE-SAFE® system.
Data exchange in the final second
The vehicle-vehicle communication using radio technology can make an important contribution to ensuring that safety systems used in Mercedes models are triggered appropriately for the situation at hand. At close ranges - i.e. immediately before an imminent accident - the automobiles of tomorrow would be able to exchange data related to vehicle type, mass, rigidity or geometry, allowing the activation of occupant protection systems to be tailored even more closely to the requirements of a given situation. This exchange of information could, for example, utilize RFID (Radio Frequency Identification) technology, which is already in use in warehouses and logistics applications.
Made-to-measure safety
Another of the company’s development goals is individualization: the protection systems of the future will be tailored even more precisely than before to a car’s occupants, to their height, weight, gender and other parameters - in other words, “made-to-measure” safety. It is conceivable, for example, that a vehicle’s driver, front passenger and rear passengers will program their heights, weights, genders and ages into the on-board computer at the start of a trip. This data would be used in an accident to adjust the inflation of the airbags, the force of the belt tensioners, the function of the belt force limiters or the position of the steering column to individual requirements.
The PRE-SAFE® functions - for example, the automatic positioning of the front passenger seat before an accident - could also be tailored to the occupants’ height.