New Benz "reacts" to help save passengers

Automakers often flaunt how well their cars react in handling the road. Now they may well start touting how well they react in protecting occupants in the event of an accident. In fact, such publicity has already started regarding rollover protection/prevention in advanced SUVs.

On the 2003 Mercedes S-Class sedan, a Pre-Safe system senses a possible collision seconds in advance and activates pre-crash measures. Mercedes engineers developed the system because company accident researchers concluded that roughly two thirds of accidents are preceded by emergency braking, skidding, or a sudden evasive maneuver-which can offer up to five seconds-a potential lifesaving window. "Making use of this relatively long interval opens up new dimensions in occupant protection," says Rudolf Schoeneburg, head of safety development.

The Mercedes system uses existing sensors for the electronic stability system to measure steering angle, vehicle yaw, and lateral acceleration to determine fishtailing (oversteer) or plowing ahead (understeer). Braking system data is also factored in. If an accident appears imminent, Pre-Safe first tensions the seatbelts using new resetable electric pretensioners, in addition to activating the existing pyrotechnic tensioners upon impact. If any of the power seats are reclined, the system brings them to a more vertical position. Detection of a skid, as a precursor to a rollover, sees the sunroof closed for greater overhead protection. If a crash is averted, the tensioners relax.

Future extensions of the system might result in extending bumpers, "smart" crumple zones tailorable to the situation, and movable interior door panels to keep occupants more distant from crumple zones. And sensors that detect approaching objects around the car could give additional warning signals.