Anyone who has done a bit of traveling in the rear seat of older model cars will likely have encountered the case of the missing buckle, where the seat-belt buckle has wormed its way down in the gap between the upholstery. While that may not be so much of a problem nowadays, Mercedes-Benz has developed an active seat-belt buckle that not only emerges from the upholstery when the rear doors are opened to make finding the buckle easier, but also improves safety by reducing the belt slack once the passenger is strapped in.

When the rear doors of the vehicle are opened, an electric motor is activated to extend the seat-belt buckle as much as 70 mm (2.7 in). The insertion slot is also illuminated, which Mercedes hopes will attract the passenger's attention and prompt them to buckle up. It is also intended to make it easier for children to fasten their seat-belt, particularly in the dark. Once the belt tongue is inserted into the buckle, the electric motor is activated once more to retract the buckle a maximum of 4 cm (1.6 in) to take up the slack and ensure the belt fits correctly in the pelvis area.

The active seat-belt is also integrated with Mercedes' PRE-SAFE preventative safety system, which is activated in critical driving situations or when a critical distance from other objects is detected. When this occurs, reversible belt tensioning of up to 8 cm (3.1 in) is applied to the belt buckle to restrain the passenger more securely in the event of an accident. Mercedes says the belt buckle, which was designed using detailed virtual human models, also branches off at a lower point on the passenger's hip to reduce the risk of the pelvis pushing through under the belt.

Mercedes has also thought about making unbuckling easier - an important consideration for freeing passengers from vehicles involved in an accident. Provided the electrical system is intact, the belt buckle will extend and the buckle illuminated as soon as the doors are opened - by rescue personnel, for example - or when the system has detected a crash and verified that the vehicle is stationary.

The active seat-belt buckle is set to enter series production in one of Mercedes' luxury-segment models shortly. Ultimately, the automaker says the new system will replace the pyrotechnic belt tensioning system, which is triggered in the event of an actual accident and has been standard in Mercedes vehicles for many years.

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