- The Washington Times - Friday, November 2, 2001

Mercedes-Benz recently previewed an occupant protection system that detects imminent collisions and deploys protective devices before an accident occurs.

The PRE-SAFE system is part of Mercedes' long-range goal of equipping cars with computers that can initiate accident prevention before passengers are aware of danger. The PRE-SAFE system deploys in phases. Part of the system consists of new seat belt tensioners and automatically adjusting seats. Later, Mercedes plans to introduce active body structure and interior components.

PRE-SAFE emerged from a theory developed after Mercedes safety teams determined that accident protection can begin in the period between a driver's realization that an accident is going to occur and the actual crash. The engineers believe that protective systems can be deployed during this brief interval without driver intervention.

Tensioners and self-adjusting seats are only a small part of the system. Mercedes has also tested automatically extending bumpers and "smart" crash boxes in the front of the vehicle. If an accident doesn't happen, the PRE-SAFE systems would reset themselves to their original positions, saving on repair costs.

The automaker has also evaluated movable interior door panels and sensor-controlled seats. These systems would complement existing passive systems, such as seat belts, side airbags and side air curtains. Vehicles would still have anti-lock brakes, Brake Assist and Electronic Stability Control systems.

The technology works with new sensors that continuously monitor drivers, vehicles and road surfaces so that when danger is indicated, PRE-SAFE is automatically activated. Mercedes engineers note that the CLK Cabriolet already has an anticipatory rollover protection system. The job of PRE-SAFE is to activate when vehicle sensors detect that the vehicle is about to have an accident.

When that occurs, front and rear seat belts will be supplied with more tension to prevent forward movement during panic braking. Also, front and rear seat cushions automatically tilt back and door panels move inward to form a protective shield around occupants.

Dr. Rodolf Schoneburg, chief of safety development, says, "In the future we will be able to use the time interval between recognizing a dangerous situation and the point at which the actual impact occurs to prepare the car for the impending crash and give the occupants the best possible protection."

PRE-SAFE deploys in various stages: Warning phase sensors detect dynamic vehicle limits and illuminate a yellow warning symbol on the instrument panel. Assistance phase activates ABS, Brake Assist and ESP.

PRE-SAFE phase commences when probability of accident is detected and systems are moved to a precautionary state. If an accident is avoided, PRE-SAFE systems revert to their original standby state.

Light impacts of up to 9 mph front extending bumpers and crash boxes absorb energy. Airbags are prevented from deploying if their assistance is not needed. Accidents with greater impacts activate belt tensioners and deploy front airbags. Tests show that forward body movement can be reduced by 150 mm and lateral movement up to 300 mm. Side airbags and curtains are deployed in side impacts while the fuel supply to the engine is cut off. A knee bolster is also extended from within the dash panel to limit crash forces on the legs. In serious accidents, front airbags are deployed with greater force and belt force limiters are deployed.

Recovery phase unlocks doors after the accident, and the emergency Tele-Aid system calls emergency response teams and guides them to the location of the accident. A hazard warning flasher is also activated.

How the system works: A dynamic sensor system checks vehicle speed, braking force, brake pedal speed, wheel slip, yaw acceleration, suspension travel, steering speed and tire pressure, using these inputs to calculate if an accident is about to happen. Ultrasonic, infrared or radar technology determines distance from a possible crash obstacle and angle of impact. The system is even capable of determining if a crash with a larger vehicle is imminent to provide more protection to occupants.


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