Braking Bag: a braking parachute for the car | Daimler > Technology & Innovation

The ESF 2009 Experimental Safety Vehicle

Braking Bag: a braking parachute for the car

Airbags in cars have previously only been used as a restraint system for
the occupants. In the future they might also be a PRE-CRASH- component, activating an auxiliary brake in the vehicle floor and improving both decel-eration and compatibility with the other vehicle involved in the accident.

Energy is not only reducible by braking the road wheels: jet fighters and drag-sters use braking parachutes, for example. And as early as 1952, Mercedes-Benz was already experimenting with an air-brake at the Le Mans race: when deceler-ating, the driver was able to move a metal panel on the roof of his racing SL to a vertical position. Even earlier, coachmen used special wheel chocks. These were placed in front of one of both rear wheels on long downhill gradients, and their iron-clad base helped to brake the vehicle during the descent.

This is an old idea that Mercedes safety researchers have revitalised on a similar principle with the Braking Bag, an airbag installed between the front axle carrier and the underbody panelling. If the sensor system concludes that an impact is in-evitable, the PRE-SAFE® system not only initiates automatic emergency braking. At the same time the Braking Bag is deployed just before the crash, supporting the car against the road surface by means of a friction coating. The vehicle's ver-tical acceleration increases the friction and has an additional braking effect be-fore the impact. The Braking Bag uses the PRE-CRASH sensors in Mercedes-Benz cars, which are already able to initiate preventive occupant protection measures in critical driving situations.

There are several advantages to this unusual auxiliary brake:

The rate of deceleration is briefly increased to over 20 m/sec/sec. This scrubs additional energy beyond the potentials of a wheel brake, thereby reducing accident severity.
Because the car is raised upwards by up to eight centimetres within a short time, the dive effect that occurs with conventional brakes is sub-stantially compensated. This improves geometrical compatibility with the other party in an accident.
This vertical movement also improves the effects of the restraint systems: the seats move towards the occupants by around three centimetres, which enables the belt tensioners to take up more slack. The high decel-eration rate before the impact has a "pretensioning" effect on the occu-pants, so to speak.
Downward support for the vehicle during the crash reduces the typical diving motion during a collision.

All in all, the braking airbag has the effect of an additional crumple zone. Mercedes engineers have calculated that even at a low 50 km/h, the additional deceleration has the same effect as lengthening the front end by 180 mm. Initial driving tests in a C-Class have already shown the effectiveness of this new auxil-iary brake – though it will still be some time before the Braking Bag becomes another component of the PRE-SAFE® system.