Safety passenger cell: Soft shell, hard core

Stuttgart, Dec 12, 2005
  • January 23, 1951: Daimler-Benz files a patent application for the safety passenger cell
  • First-time incorporation in the W 111 series of 1959
  • The Vision of Accident-free Driving – the leitmotif for all development work revolving around automotive safety
The safety cell for passenger cars was an epoch-making invention – for which Daimler-Benz filed a patent application on January 23, 1951. Since then, patent no. 854 157 has been the basis for passive vehicle safety development throughout the automotive industry. The safety passenger cell is just one from a seemingly inexhaustible pool of ideas conceived by Daimler-Benz engineer Béla Barényi.
Barényi was the brain behind countless patents concerned with vehicle safety. He realized at a very early stage that the bodywork structure had to be included in safety considerations by all means and even be made a focus of all relevant efforts. In the years after World War II, he worked on the draft for a car of the future. The result was the Terracruiser, a six-seater vehicle with a centrally located driver’s seat, which had more to offer than American dimensions and a variable interior. A crucial feature of the vehicle study was the cell-type layout of the bodywork, with a structurally very strong passenger cell in the middle, which was flexibly connected to deformable crash cells at the front and rear. This was the prototype of the rigid safety cell with front and rear crumple zones. The three-seater Concadoro designed at the same time also featured this three-cell bodywork structure.
This design was the result of a logical thought process – Barényi knew that a car body which as a whole is built to be stiff and hardly deformable does not necessarily protect the occupants of a car but on the contrary may even inflict serious injuries because the entire impact energy is transmitted to the occupants with virtually undiminished strength, causing not only external wounds but also the most severe internal injuries. To prevent this from happening, impact energy has to be reduced – and this is exactly the purpose of the crumple zones in front of and behind the stiff safety passenger cell. In the crumple zones, the sheet metal structures are specifically designed so as to deform under impact, thereby absorbing impact energy which, in turn, prevents the people inside the safety passenger cell from being subjected to the full impact forces. The functioning of this principle is borne out by the typical picture of a car with safety passenger cell and crumple zones after an accident: While the front or rear end is completely smashed, the doors to the interior compartment can still be opened without problem.
One result of the patent was specific crash testing staged to investigate the deformation of the bodywork. You may smile about the first tests made at Mercedes-Benz in this field, when the engineers still used empty pickle cans as crumple zones. These nevertheless served their purpose before being rapidly replaced by more professional approaches. Today, crash tests are staged in special facilities on the factory grounds, and they haven’ t become outdated in the age of the computer, either. While it is true that the latter helps in computing the bodywork and also in the simulation of accidents, the best object for investigation continues to be the real thing – the vehicle itself.
The W 111 series of 1959 was the first Mercedes-Benz car to feature modern safety bodywork with crumple zones front and rear and a passenger cell that was highly resistant to deformation. Today, every Mercedes-Benz is designed along these lines, with numerous additional technical developments aimed at enhancing motoring safety having been incorporated over the years. They are all geared to the Vision of Accident-free Driving pursued by Mercedes-Benz.

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