Technical information

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An optical fibre is integrated between the bumper support and impact absorber. The optical fibre is connected to a sensor
and passes in a loop around to the opposite side of the vehicle before heading back to the sensor again.
A force acting on the optical fibre deforms it between the deformation structures. This causes the light in the optical fibre
to be attenuated. The acting force is proportional to the light attenuation. A characteristic signal is thus generated by the
differing damping action on the light, the nature of which depends on the mass and rigidity of the colliding object.
This signal is measured by the sensor and sent along a data line to the Crash Safety Module (ACSM). The Crash Safety
Module (ACSM) uses this data and the data from the central acceleration sensor in the bumper to determine whether the
threshold value for detecting a pedestrian collision has been reached or exceeded. It decides whether to activate the
engine compartment lid actuators based on the result.
The actuators are activated pyrotechnically and lift the engine compartment lid. Gas pressure springs also support the
engine compartment lid when raised.
The active engine compartment lid is only triggered at speeds of approx. 20 –55 km/h. For safety reasons the system
may activate on those rare occasions where a pedestrian collision cannot be unequivocally ruled out, e.g.:
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a crash against a dustbin or bollard
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a collision with an animal
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hitting a rock
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driving into a snowdrift
After the active engine compartment lid is triggered, a Check Control message is shown in the instrument cluster and in
the central information display.
The engine compartment lid cannot be returned to its initial position after activation. Active pedestrian protection is only
re-established after a component change has been carried out. After the pedestrian protection has activated, it is only
possible to continue driving carefully at a maximum speed of 80 km/h.
Body and materials
Structure of the body
Thanks to high-strength steels, greater wall thicknesses and a multi-shell construction, the stability of the vehicles is
1 Right engine compartment lid catch (with actuator) 6 Optical fibres
2 Bowden cable 7 Central sensor (acceleration)
3 Right engine compartment lid hinge (with actuator) 8 Actuator (on engine compartment lid hinge)
4 Left engine compartment lid hinge (with actuator) 9 Sensor (optical fibre)
5 Left engine compartment lid catch (with actuator) 10 Deformation structure
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