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.
The pedestrian protection is a complete system consisting of pedestrian protection sensors, control unit and actuators.
Depending on the series and model, either a crash safety module (ACSM) or an MRS control unit is installed.
Brief component description
The following components are described for the pedestrian protection system:
ACSM or MRS: Crash safety module / multiple restraint system
The crash safety module (ACSM) or MRS control unit evaluates the signals from the pedestrian protection sensors ("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 or MRS control unit 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 or MRS control unit.
The graphic below shows an example of the crash safety module in the E93.
Pedestrian protection sensors
The following pedestrian protection sensor are installed in the bumper:
- Pedestrian protection sensor (with optical fibre)
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 or MRS control unit.
- Pedestrian protection sensor (acceleration sensor)
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 or MRS control unit.
The following graphic shows the and example of the pedestrian protection sensors on the E93.
Actuators
Following actuators for the pedestrian protection are described:
- Pedestrian protection actuator on front left and pedestrian protection actuator on front right The actuators are not installed in all model ranges and models, for example not E8x and E92/E93 M3. When the crash safety module or MRS control unit transmits a trigger signal, the actuators are triggered 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.
- Actuator for pedestrian protection on rear left and actuator for pedestrian protection on rear right When the crash safety module or MRS control unit transmits a trigger signal, the actuators are triggered as follows: The ignition squib in the pyrotechnic component ignites the propellant charge. The pyrotechnic actuator contains a priming cap whose propellant charge cuts a shear pin in the hinge. After the separation, the propellant charge raises part of the hinge and this the engine compartment lid is raised within a few milliseconds by several millimeters (e.g. 50 millimeters).
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.
System activation
The Crash Safety Module or MRS control unit detects a pedestrian impact due to the input signals of the following pedestrian protection sensors:
- 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 or MRS control unit.
If only one pedestrian protection sensor sends the corresponding signal, the Crash Safety Module or MRS control unit 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 or MRS control unit always triggers all the actuators for pedestrian protection. This triggering is pyrotechnical.
With spring force and propellant charge, the engine compartment lid then is then raised by several millimeters at the front and (optionally) 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
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.