Perfectly coordinated and secured

Kai Jennoch from the PSW restraint systems /airbags development department and his colleague Valentin Berrueco from calculation/ simulation supported the customer Audi in the development of passive safety systems of the Audi e-tron. On the one hand, their task has been to develop the corresponding components together with other PSW colleagues from seatbelt and air bag development in coordination with the Audi specialist departments.

On the other hand, their responsibility has been to guarantee the perfect interplay of components in the complete system. In addition they have jointly secured the systems through virtual simulation methods. This was the first time PSW experts designed the passive safety systems of an electric vehicle. But what difference does this make to a vehicle with a combustion engine?

‘It is a question of the pulse’, says Kai, who often loses himself in specialist terminology during the discussion, therefore causing his listener to frown. You notice how passionate he is when he enthuses about his subject. He explains patiently: ‘In a vehicle with conventional drive the engine offers a buffer zone. During a crash the front folds up bit by bit, while the engine provides resistance, to decrease the speed. The pulse, in other words the delay, is correspondingly large. Of course electric cars have no comparable engine, so that depending on the design of the front end of the vehicle, the front folds more quickly. Through this the pulse is less.’ Of course as soon as the structure deformed by the crash meets the entire battery case, the delay rapidly increases, because the battery is protected in such a way, that it cannot be deformed.

The experts achieved the optimum design of systems while using particular systems to intelligently trigger seatbelt tensioners and air bags. On the one hand this information is provided by capacitive seat recognition. The information specifies whether the seat is occupied or not. On the other hand, a switch device in the seat can estimate how large and heavy the occupant is.
Based on this information and in consideration of the deformation behaviour of an electric car, Kai and Valentin coordinate the trigger time of seatbelt tensioners and air bags to each other. The interaction of both systems must be perfectly harmonised. In the first ignition threshold the seatbelt tensioner is first triggered and shortly after that the air bag. Some air bags have additional levels’, according to Kai. In addition the air bags must be correspondingly softer or harder, depending on the dimensions of the passenger, to provide the best possible protection. For instance, the air bag must be softer for a smaller woman than for a large man.
The different legal framework conditions posed a further legal challenge. Kai and Valentin must ensure that the design conforms to specific guidelines. For instance only limited forces may act on some body regions, which are specified in kilonewtons. These guidelines vary from market to market, which the engineers must consider during the development.