Pedestrian Protection System: Description and Operation
Pedestrian Protection
Pedestrian protection
The pedestrian protection system has the following task: To detect an accident situation between a pedestrian and a passenger car in the area of the engine compartment lid and to selectively activate the system depending on certain marginal conditions.
Pedestrian protection is a complete system consisting of pedestrian protection sensor(s), control unit and actuators.
Brief component description
The following components are described for the pedestrian protection system:
Crash safety module
The crash safety module (ACSM) evaluates the signals from the pedestrian protection sensor(s) ("ACSM" stands for "Advanced Crash Safety Module"). If a collision with a pedestrian is registered by the pedestrian protection sensor(s), the crash safety module always triggers all the actuators for pedestrian protection.
Pedestrian protection only triggers within a defined driving speed range. Outside of the defined driving speed range, the function is blocked in the crash safety module.
Pedestrian protection sensors
The pedestrian protection system is equipped either with one pedestrian protection sensor (with optical fibre) or with 3 pedestrian protection sensors (acceleration sensors) or a combination of optical fibre and acceleration sensors.
- Pedestrian protection sensor (with optical fibre)
An optical fibre is integrated in the bumper. The optical fibre is a constituent part of the pedestrian protection sensor. Through the sensor, the light in the optical fibre is sent out at one side of the bumper to the other end of the bumper and back to the sensor again via a loop.
A force acting on the optical fibre alters this in its structure. 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 light attenuation in dependence on the mass and rigidity of the colliding object. This signal is recorded in the evaluation electronics of the sensor and transmitted via a data line to the Crash Safety Module.
- Pedestrian protection sensor (acceleration sensor)
A number of pedestrian protection sensors are installed in the bumper. The right pedestrian protection sensor is supplemented by the centre pedestrian protection sensor and the left pedestrian protection sensor. All sensors are common parts.
The pedestrian protection sensor is an acceleration sensor. The acceleration values picked up by the micro-mechanical acceleration sensor are converted into digital signals and sent cyclically to the crash safety module.
- 2 pedestrian protection sensors (optical fibre and acceleration sensor)
One optical fibre and one acceleration sensor are installed in the bumper. The acceleration sensor is installed in the centre at the bumper.
Actuators
Using the F01 as an example, the following actuators are described for the pedestrian protection system: Pedestrian protection actuator on front left and pedestrian protection actuator on front right If the crash safety module sends a trigger signal, the actuators trigger as follows: The ignition squib in the pyrotechnic component ignites the propellant charge. The pyrotechnic actuator contains an ignition squib whose propellant charge shifts a plunger with bolt to unlock the engine compartment lid catch.
After this unlocking, the engine compartment lid is raised within a few milliseconds by several millimeters (e.g. 30 millimeters) by the force of the springs in the engine compartment lid catch.
- Front left actuator for pedestrian protection
The actuator is installed in the front left engine compartment lid catch.
- Front right actuator for pedestrian protection
The actuator is installed in the front right engine compartment lid catch.
Actuator for pedestrian protection on rear left and actuator for pedestrian protection on rear right If the crash safety module sends a trigger signal, the actuators trigger as follows: The ignition squib in the pyrotechnic component ignites the propellant charge. The pyrotechnic actuator contains a ignition squib whose propellant charge unlocks the two retaining bolts in the lid. After this unlocking, the engine compartment lid is raised within a few milliseconds by several millimeters (e.g. 50 millimeters) by the force of the springs in the actuator.
- Rear left actuator for pedestrian protection
The actuator is installed in the rear left engine compartment lid hinge of generation K2.
- Rear right actuator for pedestrian protection
The actuator is installed in the rear right engine compartment lid hinge of generation K2.
System functions
The following system functions are described for the pedestrian protection system:
Functional networking
The following graphic shows the functional networking for the pedestrian protection system.
- The following graphic shows the pedestrian protection system with 3 pedestrian protection sensors (acceleration sensors).
- The following graphic shows the pedestrian protection system with one pedestrian protection sensor with optical fibre.
- The following graphic shows the pedestrian protection system with 2 pedestrian protection sensors (optical fibre and acceleration sensor).
System activation
The Crash Safety Module detects a pedestrian impact due to the input signals of the following pedestrian protection sensors:
- Pedestrian protection system with 3 pedestrian protection sensors (acceleration sensors):
For impact detection at least one of the 2 pedestrian protection sensors must send a corresponding signal to the Crash Safety Module.
If only one pedestrian protection sensor sends the corresponding signal, the Crash Safety Module does not trigger the actuators for the pedestrian protection.
- Pedestrian protection system with one pedestrian protection sensor (optical fibre).
For the impact detection the pedestrian protection sensor sends a corresponding signal to the Crash Safety Module.
- Pedestrian protection system with 2 pedestrian protection sensors (optical fibre and acceleration sensor)
For impact detection the corresponding signal from the two pedestrian protection sensors must be sent to the Crash Safety Module.
If only one pedestrian protection sensor sends the corresponding signal, the Crash Safety Module does not trigger the actuators for the pedestrian protection.
If a collision with a pedestrian is registered by the pedestrian protection system, the crash safety module always triggers all the actuators for pedestrian protection. This triggering is pyrotechnical.
With spring force, the engine compartment lid is then raised by several millimeters at the front and rear. This enlarges the space between the inner panel of the engine compartment lid and the add-on parts to the engine as well as on the body. The enlarged space increases the possible deformable area of the engine compartment lid in the event of a head impact. Furthermore, the rigid connection of the engine compartment lid is changed into an elastic connection by the springs in the actuators. This enables improved energy dissipation when the head strikes the engine compartment lid.
Notes for Service department
Resetting the engine compartment lid hinge of generation K2
After the system has been triggered by a sensor signal, the engine compartment lid can be reset. Exerting excess pressure on the opened engine compartment lid (towards open) mechanically locks the rear actuators in the engine compartment lid hinge of generation K2.
The actuators in the front engine compartment lid catches are automatically reset after opening and subsequently closing the engine compartment lid.
General notes
After the pedestrian protection system has triggered, it is obligatory to replace the actuators for renewed activation of the system. The triggering has used up the ignition squib and propellant charge in the pyrotechnic components. We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.