Protection concept specific to Mercedes-EQ and extensive crash tests

Jan 20, 2021
Stuttgart

A true Mercedes: in the case of the EQA, this is an accolade that also applies with respect to the protection of occupants and other road users. Naturally the car had to go through the brand's comprehensive safety development process and familiarly rigorous crash test programme. For an electric car, the internal requirements are even more stringent: as far as the battery and all other components that carry electrical current are concerned, strict safety standards apply, which in many cases go beyond the legally specified requirements.

On the basis of the robust structure of the GLA, the body of the EQA was adapted to meet the particular demands that face an electric car. While the side walls are identical, the main floor section was modified in order to accommodate the battery. The battery sits within a frame made out of extruded sections. This takes on a structural function which until now was maintained by the cross members in the underfloor. A battery guard in the front area of the battery is able to prevent the energy storage unit from being pierced by foreign objects. The ground clearance of more than 200 milli­metres is a further advantage. The lowest point of the vehicle is not the battery, but the side skirts.

Because the EQA is heavier than a GLA, more energy needs to be absorbed in the event of a crash. The supporting structures at the front and rear were adapted to accommodate this requirement by the use of thicker materials.

The accident safety of the EQA has been validated in the Mercedes-Benz Technology Centre for Vehicle Safety (TFS). In this state-of-the-art crash centre, prototypes with large electric batteries were also tested under stringent crash conditions. The black panel front end was also tested with regard to its fracture behaviour in order to comply with the requirements for pedestrian protection.

In all aspects of the vehicle configuration that are relevant in an accident, the legal requirements were further bolstered by internal testing requirements and test criteria derived from the findings from real-life accident scenarios. One example of this work is the roof-drop test, which Mercedes-Benz uses to check the rigidity of the roof, an important factor in a rollover accident, for example. In the roof-drop test the body falls from a height of 50 centimetres at a slight incline onto the roof structure, so that initially only one of the two A-pillars is affected.

Individual aspects of accident safety were tested in component tests undertaken with the battery in the development centre. The test criteria included, for instance, the reaction of the battery under a shock load or if pierced by a foreign object. The punching test, for example, uses a test object 50 by 50 millimetres in size to test, for instance, what damage a trailer coupling left lying in the road can cause to the underbody. The effect of the battery overheating or being overcharged was also tested.

Safety concept for the high-voltage system: automatic shut-off in a crash situation possible

The extensive experience of Mercedes-Benz with high-voltage drive systems has led to a multi-stage safety concept. The high-voltage system can be automatically switched off in a crash, reversibly or irreversibly depending on the accident severity. Another feature of this comprehensive safety concept is that the charging process is automatically curtailed if an impact is detected when the car is stationary at a rapid-charging station (DC charging).

In addition to this independently functioning monitoring system, the EQA is fitted with a special disconnection point which can be used by the rescue services to switch off the high-voltage system.

Restraint systems: partnership with the safety body shell

The most important restraint system is the seat belt. The driver and front passenger are provided with three-point seat belts with pyrotechnic belt tensioners and belt force limitation. In combination with the PRE-SAFE® system (optional extra), the front seats are additionally equipped with electrically reversible belt reel tensioners. Both the outer rear seats are fitted with a three-point seat belt with reel tensioner and belt force limiter. The centre belt in the second row is a standard three-point automatic belt.

The new EQA is equipped as standard with driver and front passenger airbags, a driver kneebag and windowbags. The windowbags cover the first and second row of seats. They extend a long way forward as far as the A-pillar, thus offering particularly high protection potential. Thorax-pelvis side airbags in the front are likewise standard, and available as optional equipment for the second row.

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