Mercedes-Benz has revealed its S-Class hybrid-based ESF (Experimental Safety Vehicle) 2009, which brings a new dimension to airbag applications. Dubbed a "braking bag," an airbag is being developed as a pre-crash retardation aid. Positioned between the front axle carrier and underbody paneling, it deploys milliseconds before impact when the car’s Pre-Safe system has decided that a front-on impact is inevitable.
The deceleration rate is said to increase briefly to more than 20 m/sec² (66 ft/s²), effectively doubling the retardation rate compared to wheel brakes on a dry surface. The car’s front end is also raised by 6 cm (2.4 in), compensating for a nose-down attitude under maximum braking and improving geometrical compatibility with a vehicle ahead and also improving the efficacy of restraint systems.
The braking bag supports the car and is isolated from road surface abrasion by an aluminum and rubber or possibly carbon-fiber shield. The vehicle’s vertical acceleration increases the surface friction.
The system effectively acts as an additional crumple zone. The team involved in its development estimate that, at a 50-km/h (31-mph) impact speed, the additional deceleration provided by the braking airbag has the same effect as lengthening the front end by 180 mm (7.1 in). The system could be fitted to a production car in five to 10 years.
The ESF 2009 is the first such vehicle to be built by Mercedes for 35 years and was publicly revealed at the Enhanced Safety of Vehicles Conference in Stuttgart.
As well as the braking bag, the car incorporates several other safety technology R&D projects. One of the most extraordinary is the use of inflatable metal structures. Typically they can be used in vehicle doors to resist side-impact intrusion.
In their "uninflated" state, they can be packaged easily and do not markedly intrude on design or styling parameters and save mass—about a 500-g (18-oz) reduction per door in an S-Class. In the event of an impact, a gas generator, supplied by Autoliv and similar to the type used for airbags, produces an internal pressure of up to 20 bar (290 psi) in the structure, which then unfolds or morphs to present a shape that has greater stability under high loads. The system could be used for other parts of a car’s crashworthy elements.
It would be essential for the car’s pre-crash technology to be 100% reliable because active deformation is not reversible.
A further aspect of Pre-Safe in the research car is a pulse system that nudges the driver and front passenger inboard by up to 50 mm (2 in) immediately before a side impact, the acceleration reducing the loads acting on the seat occupants. The system is being developed on the basis of a dynamic multicontour seat in the new E-Class.
Pre-Safe 360°, fitted in the research car, also monitors the rear of the vehicle at ranges up to 60 m (197 ft), applying the brakes 600 ms before a rear impact. This goes against the commonly held belief that the brakes should be released before a rear-end collision. But, this action can result in a secondary accident because the struck car may be pushed into a junction or pedestrian and the driver’s feet will probably have slipped from the pedals.
Child car seats have been the subject of intensive research. That fitted to the ESF uses a tubular construction that Mercedes states offers better support and greater rigidity than types using molded plastic. Prominent side bolsters in the shoulder and head area are designed to keep the child in place and to minimize body movement during an impact. The seat is a study at present, approved to ECE R44.04 standard.
Further interesting elements of the ESF include an airbag positioned between driver and front passenger to prevent their heads clashing in an accident. In the rear, a protective pad positioned above the center armrest keeps heads apart. It can be extended and used as a head support during regular journeys.
The ESF’s lighting systems include an LED-based adaptive main beam. The main beam is in constant use, but the light distribution is adjusted for oncoming traffic from camera-derived data.
An ESF headlamp comprises up to 100 LEDs that can be individually activated. The configuration also includes a spotlight controlled by an infrared camera. If, for example, the camera pinpoints pedestrians outside the headlamp spread, the spotlight illuminates them.