Active seat-belt buckle is a new innovation for the rear seats which is currently under development by safety pioneer Mercedes-Benz and will shortly go into series production in one of the Stuttgart manufacturer’s luxury-segment models. An electric motor extends and retracts the seat belt buckle automatically. In this way, the belt slack in the area of the pelvis and thorax can be reduced and passengers are secured more firmly in sideways and lengthways directions. Active seat-belt buckle fits in with Mercedes-Benz’s integrated safety concept. In keeping with an all-embracing approach to safety, this concept covers all phases of automotive safety: from safety during driving through safety in hazardous situations and protection in the event of an accident to minimisation of the consequences of accidents.
The innovation is typically Mercedes-Benz, improving safety and comfort in one. 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. The innovation also makes it easier to assist children or people who require help in fastening their seat belts.
Active seat-belt buckle is also integrated in the PRE-SAFE® preventive safety system. This means that whenever PRE-SAFE® becomes active in critical driving situations or when a critical distance from other objects is detected, reversible belt tensioning is also effected in the rear via the active seat-belt buckle function. The restraint system and the passengers are thus better prepared for a possible accident situation. Active seat-belt buckle complements the pyrotechnic belt tensioning which has featured as standard on all outer rear seats in Mercedes-Benz vehicles for many years now. This pyrotechnic system is triggered in the event of actual impact.
The Mercedes safety experts have developed active seat-belt buckle using detailed computer models of the human body, as dummies are only able to simulate the human pelvic system along very rough lines.
“Active seat-belt buckle is another element of our ‘PRE-SAFE®’ concept, which is intended to provide our customers with optimum protection in real accident scenarios,” stresses Prof. Dr. Ing. Rodolfo Schöneburg, Head of Passive Safety and Vehicle Functions at Mercedes-Benz Cars. “After all, we aim to offer a high standard of safety not only in all model series, but also in all seats.” Active seat-belt buckle has also been developed with an eye on new markets in which the level of occupied rear seats is up to 30 percent – markedly higher than in Europe. “In the rear of premium saloons in particular, passengers tend to sit in particularly relaxed positions in the generous space which is available,” explains Schöneburg. “Active seat-belt buckle as part of PRE-SAFE® unlocks the full potential of the on-board restraint systems.”
Integration in the vehicle’s PRE-SAFE® system
Active seat-belt buckle is a moving belt buckle which can be extended by 70 millimetres and retracted by 40 millimetres via an electric motor. The belt buckle is attached via a cable to a spindle 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/easier fastening of the seat belt: Active seat-belt buckle is provided with an illuminated insertion slot, attracting the occupants’ attention to the buckle. Particularly in the dark, the belt buckle is easier to find and to connect with the seat belt tongue. In addition, the belt buckle is extended by 70 millimetres when occupants enter the rear of the vehicle, to facilitate fastening of the seat belt. In extended state 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 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 the belt fits correctly in the pelvis area.
PRE-SAFE® function for rear occupants: Active seat-belt buckle is fully integrated in the vehicle’s PRE-SAFE® system. Whenever PRE-SAFE® becomes active in critical driving situations or when a critical distance from other objects is detected, reversible belt tensioning is also effected in the rear via the active seat-belt buckle 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. This reversible function increases the belt tensioning 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 pushing through under the belt. Securing the occupants more effectively in this way reduces the stress to which they are exposed in the event of an accident. Active seat-belt buckle is set to replace the pyrotechnic belt tensioning which has featured as standard in Mercedes-Benz vehicles for many years now. This pyrotechnic system is triggered in the event of 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 verified that the vehicle is stationary, 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 belt’s opening mechanism.
In keeping with Mercedes-Benz’s integral safety concept, active seat-belt buckle covers all four areas of automotive safety – “Safe driving”, “In the event of danger”, “In an accident” and “After an accident”.
Virtual human model as an unconventional development tool
The Mercedes-Benz safety experts have developed active seat-belt buckle with the aid of virtual human models, which provide a clearer picture of what happens to a vehicle’s occupants in an accident than crash-test dummies. These digital models simulate not only the human body’s outer form, but also its internal structures, such as bones and soft tissue.
“All the crucial biological features of humans – joints, muscles, tendons, ligaments, bones – can only be simulated in very rough terms with dummies,” explains Dr Hakan Ipek, expert for virtual human models at Mercedes-Benz. “Some seated positions, such as when a rear passenger is dozing and the belt does not pass over the pelvis in the correct manner, simply cannot be recreated with a dummy,” he adds by way of example.
With virtual human models, the biomechanical characteristics of the human body are simulated in detail on a computer, enabling examination of the stress to which the model is exposed in a virtual crash test.
