by Adrian-Liviu Dorofte
e-mail: mercedesbenzblog@gmail.com

The new Mercedes-Benz S-Class: Extended protection in the rear - Top safety level in the rear

Mercedes-Benz is further reinforcing the safety system for passengers in the rear with the seat belt buckle extender, the beltbag and the cushionbag. In contrast to many other manufacturers, the seat belts in the rear already include belt tensioners and belt force limiters today.

Both systems were furthermore developed with a particular view toward new markets in Asia. There, the occupancy rate in the rear is as much as 30 percent, making it much higher than in Europe.

Reducing the belt slack: the seat belt buckle extender

With the seat belt buckle extender, an electric motor extends and retracts the belt buckle automatically. In this way, buckling up can be made more convenient, and any belt slack in the area of the pelvis and thorax can be reduced even when belting up so that passengers are secured more firmly in both the sideways and the lengthways direction. The seat belt buckle extender fits in with Mercedes-Benz's integral safety concept. In keeping with an all-embracing approach to safety, this concept covers all phases of automotive safety: from safety while driving through safety in hazardous situations and protection in the event of an accident to minimisation of the consequences of accidents.

The innovation is classic Mercedes-Benz, improving safety and comfort in one. This is because fastening seat belts in the rear is also made much simpler: the seat belt buckle emerges from the upholstery when the rear doors are opened and is provided with an illuminated insertion slot. Simplifying use of the seat belt in this manner may increase the percentage of rear passengers who buckle up. It also makes it easier to assist children or people who require help in fastening their seat belts.

The seat belt buckle extender is furthermore integrated in the PRE-SAFE® anticipatory safety system. This means that whenever PRE-SAFE® becomes active in critical driving situations or when the system detects the vehicle approaching other objects at a critical speed, reversible belt tensioning is also performed in the rear via the seat belt buckle extender function. The restraint system and the passengers are thus better prepared for a possible accident situation. In this way, the seat belt buckle extender complements the pyrotechnic belt tensioning which has featured as standard on all outer rear seats in Mercedes-Benz vehicles for many years now, and is triggered in the event of an impact exceeding a certain severity.

The seat belt buckle extender is a motorised belt buckle which can be extended upwards by up to 50 millimetres and retracted by up to 40 millimetres. The belt buckle is attached via a cable to a nut which runs on a spindle, translating the electric motor's rotary movement into a linear movement.

The following functions are carried out by means of this movement:

- Seat belt reminder/fastening aid: the seat belt buckle extender is provided with an illuminated insertion slot, attracting the occupants' attention to the buckle. Particularly in the dark, this makes it easier to find the belt buckle and connect it with the seat belt tongue. In addition, the belt buckle is extended by up to 50 millimetres when occupants enter the rear of the vehicle, to facilitate fastening of the seat belt. When extended, the belt buckle is more readily accessible and it is easier to insert the belt tongue. Both functions are activated when the doors are opened by passengers entering the rear of the vehicle.

- Minimised belt slack: after the belt tongue has been inserted, the belt buckle returns to its original position. This reduces any belt slack in the area of the pelvis and thorax, and ensures that the belt fits correctly in the pelvis area.

- PRE-SAFE® function for rear occupants: the seat belt buckle extender is fully integrated in the vehicle's PRE-SAFE® system. Whenever PRE‑SAFE® becomes active in critical driving situations or when the system detects the vehicle approaching other objects at a critical speed, reversible belt tensioning is now also performed in the rear via the seat belt buckle extender function. The restraint system and the passengers are thus better prepared for a possible accident system. In contrast to its extended position to facilitate fastening of the seat belt, the belt buckle is retracted by approx. 40 millimetres instead. This reversible function tightens the belt on the occupant by up to 80 millimetres. In addition, the belt buckle branches off at a lower point at the occupant's hip. This reduces the risk of the pelvis submarining under the belt. Securing the occupants more effectively in this way can reduce the strain to which they are exposed in the event of an accident. The seat belt buckle extender complements the pyrotechnic belt tensioning which has featured as standard in Mercedes-Benz vehicles for many years now and is triggered in the event of an actual impact.

- POST-SAFE functionality: to facilitate the rescue of occupants and to assist rescue personnel or the occupants themselves in unbuckling the seat belts, the belt buckle is extended once again as soon as the doors are opened by rescue personnel or the occupants themselves after the system has detected a crash and the vehicle has come to a standstill, provided that the on-board electrical system is intact. The raised belt buckle position allows better access from inside the vehicle, while illumination of the buckle draws attention to the opening mechanism.

An airbag for seat belts: the beltbag

The beltbag is an inflatable seat-belt strap that reduces the load on the ribcage in a head-on collision and is thus able to reduce the risk of injury to passengers in the rear. Because dummy measurement technology is not capable of quantifying the benefits resulting from a wider belt strap, such as the lower force exerted on occupants in the rib area in particular, the safety experts at Mercedes have been working intensely with virtual human models too, as such computer-generated models make it possible to obtain detailed findings on the biomechanical strain during a collision.

Should the crash sensors detect a severe frontal impact, the airbag control unit will trigger deployment and inflation of the beltbag. A gas generator then inflates the multi-layered belt strap with Velcro seams to nearly three times its normal width. The resulting larger surface area is able to better distribute the force acting on the seat occupant, thereby reducing the risk of injury.

The beltbag is used in exactly the same way as a conventional seat belt. The belt strap's design is different from that of the standard belt though, and received top marks in practical trials for being extremely comfortable to wear and for its extra-soft belt strap edge.

An airbag for the seat: cushionbag

If the S-Class is equipped with the Executive seat (reclining seat), the seat includes the innovative cushionbag as standard. The airbag is located under the seat cushion upholstery, but on top of the plastic seat shell, which is moved by the seat mechanisms. This means that the airbag is always in the right position relative to the occupant.

In an accident, with the occupant in a reclined position on a flat seat cushion, without additional measurers there would be a danger of the pelvic area sliding beneath the seat belt (submarining). This can be prevented by the cushionbag, as it raises the front section of the seat cushion upholstery. The airbag is only activated if the seat is in the reclined position during a crash. It is not activated in the upright position, as there is then no danger of submarining.

Credits: Daimler AG

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