- Systematic crash tests yield fundamental findings
- First dummy named Oscar
- Trailblazing experimental safety vehicles in the 1970s
At the end of the 1950s, Mercedes-Benz started practical testing for safety research purposes. Initially, individual components were tested – by means of impact tests, for example – but entire systems were also tested, such as the seat belt which became available in 1958.
In 1959, spectacular crash testing was started using Mercedes-Benz vehicles as the basis for safety research. For the systematic crash tests, the test vehicles were first accelerated by means of a towing system such as those used to launch gliders. With the Mercedes-Benz towing unit, sedans fresh from the assembly line could be launched into the air. This was necessary because right from the start of crash testing at Mercedes-Benz, the engineers did not just simulate collisions by running vehicles into a fixed barrier, they also simulated rollovers. To achieve this, the test vehicles were run at a speed of 75 (47 mph) to 80 km/h (50 mph) on to a so-called corkscrew ramp, which gave the automobiles the necessary twist so that they lifted off into mid-air and landed on their roofs. These tests led to the installation of stabilizing structures in the bodywork.
The hot-water rocket
Accelerating a test vehicle with a towing unit was not an ideal method. Dr. Ernst Fiala created a solution in 1962 – for the crash experiments performed by Karl Wilfert’s team, he designed a hot-water rocket which propelled the vehicles without a tow rope. The device was mounted on a single-axle trailer positioned behind the test vehicle and consisting of a pressure tank, a quick-opening valve and a discharge nozzle. The tank was filled with water to roughly 75 percent of its capacity, and in order to produce thrust, the tank was heated until the temperature of the water had reached approx. 260°C (500°F). The resulting excess pressure propelled automobile and rocket forward after the valve was opened, accelerating the unit to over 100 km/h (62 mph). However, the hot-water rocket sometimes propelled the automobile in such a manner that it missed the barrier or ramp altogether.
Crash tests without such incidents became possible from 1973 onwards at the new test centre in Sindelfingen. On the 65-meter acceleration track, a linear motor producing a thrust force of 53,000 Newton accurately pulled the automobiles into a 1000-ton barrier, which rested on a very sensitive force measuring platform.
The crash test facility was then thoroughly renovated in 1998 with the creation of the Mercedes-Benz Technology Center (MTC). At an expense of 2.3 million euros, the facility was refurbished with state-of-the-art technology. The length of the acceleration track was increased to 95 meters; as a result, all types of crash test variants were now possible at the facility. In particular, this included offset crashes, in which only part of the frontal width of the vehicle impacts the obstacle or other party and which in reality occur much more frequently than head-on vehicle collisions. The test sequences are no longer recorded by a high-speed film camera, but by video technology. The very high frame rate has been maintained so that the crash tests can be evaluated in extremely slow motion. The facility was also equipped with a roof during the renovation so that passenger car and commercial vehicle testing can now be performed regardless of the weather.
Oscar: The first crash test dummy at Mercedes-Benz
From the start of crash testing at the company, not only vehicles were used to assess the effects of crashes. This is because Oscar was acquired as the first crash test dummy at the same time. Measuring instruments in the head and chest of the dummy provided information on the loads acting on the driver during an accident. Sandbags and mannequins initially took the place of the front passenger. Nevertheless, dummies were soon also collecting crash test data from the front passenger seat and rear bench. Individual dummy designs were used to measure specific injuries and to represent persons of different build and age. Increasing computer capabilities then allowed dummies to be replaced by mathematical multi-body systems. The first digital crash computations with overall vehicle models were performed for the E-Class of the 124 series.
One aim of Mercedes-Benz crash testing is to achieve results that are as realistic as possible. Consequently, the head-on collision is increasingly being replaced by the offset collision. In 1992, an offset frontal collision was performed against a deformable barrier for the first time, providing results that correspond even more closely to the behaviour of a vehicle in a real-world accident. A deformable barrier was developed for this type of experiment in Europe, its design decisively influenced by test results from the Mercedes-Benz Safety Center in Sindelfingen. After the introduction of the offset barrier test, this new European test procedure represented another big step towards realistic crash testing. In 1993, the offset crash against a deformable barrier made from metal honeycomb material at 60 km/h (37 mph) and with a 50 percent overlap became the new Mercedes-Benz standard.
In addition to the data collected in these crash tests, other findings are included in the safety development process. In 1966, for example, analysis of real-world accidents involving Mercedes-Benz vehicles began. This project led to the start of official accident research in Stuttgart and its surroundings in 1969, carried out by the newly founded Accident Analysis department. Here experts examined crash vehicles, in most cases at the scene of the accident, testing the effectiveness of all available measures and proposing further improvements to Mercedes-Benz models.
The test vehicles
Test vehicles also play an important role in safety research. From 1971 to 1974, Mercedes-Benz took part in the international ESV (Experimental Safety Vehicle) program. The aim of this project was to improve passenger cars in line with the safety criteria of the US National Highway Traffic Safety Administration. The specifications called for a minimal risk of passenger injury in the following cases: a head-on impact against a fixed barrier at 80 km/h (50 mph), a head-on impact against another vehicle at 120 km/h (75 mph), a side impact by another vehicle at 50 km/h (31 mph), a rear-end collision by another vehicle at 120 km/h, and a rollover. The developments were verified by means of crash tests.
The last ESV of the Stuttgart-based company was the ESF 24 which was presented in June 1974. It was based on a production model from the S-Class (W 116 series) and provided the standard level of protection but also had a specially modified front section for researching design solutions for a head-on collision against a fixed barrier at 65 km/h (40 mph). A development report of 1975 stated that, with the ESF 24, Mercedes-Benz had achieved “an optimum compromise between the original ESV requirements and our current production vehicles.”
The ESV program was started in 1970 by the US Department of Transportation and called on motor manufacturers to build vehicles which satisfied extreme requirements in terms of active and passive safety. The first results Mercedes-Benz presented to the public were the ESF 05 (1971) and the ESF 13 (1972). Both test vehicles met the ESV specification of the US Department of Transportation, fulfilling the passenger protection requirements for a frontal impact at 80 km/h (50 mph) particularly well. The ESF 05 was one of the main attractions at a 1971 international safety conference hosted by Mercedes-Benz in Sindelfingen.
Unfortunately, however, the first Experimental Safety Vehicles from Stuttgart were approximately fifty percent heavier than the basic Mercedes-Benz 250 (W 114 series), resulting in high fuel consumption and emission levels. For this and other reasons, Mercedes-Benz compiled its own specifications and concentrated on researching passenger protection at the impact velocities considered to be most relevant (between 80 km/h/50 mph and 50 km/h/31 mph), using a three-point seat belt of European origin. The ESF 22 presented in 1973 offered protection at 65 km/h (40 mph), although it was still approximately twenty percent heavier than the base model from the Mercedes-Benz S-Class (W 116 series). The ESF 24, which was also based on the W 116, was, however, only ten percent heavier than the production car.
Mercedes-Benz derived many of the equipment features appearing in later production models from the ESV program. These included head restraints for all occupants, three-point inertia-reel seat belts, belt tensioners, a particularly rigid passenger cell with optimized front end, rear end and side structures as well as a safety steering system. The last test vehicle, ESF 24, was primarily used to test belt force limiters, airbags and seats with integrated belt anchors.
After the ESV era, Mercedes-Benz continued to use concept and test vehicles to develop safety technology. One example of this was the Auto 2000 research car, unveiled to the public in 1981, which was used to test seats with integrated belt anchors, an integrated seat child module and pedestrian-friendly bumpers. The Mercedes-Benz Development unit also set standards in the field of commercial vehicles with its test and concept vehicles, such as the 2004 safety study which was based on the Sprinter van. This concept vehicle was distinguished by low-reaching windows, roll stabilization and numerous perceptual safety innovations. In 2006, the Actros Safety Truck followed, though not as a design study. The vehicle, fitted among other things with Active Brake Assist, an emergency braking assistant, was made available on the market.