Rear PRE-SAFE®, Function - GF30.30-P-0015FQM
MODEL 218
as of year 2015
with CODE 253 (Rear impact warning and protection system)
Function requirements, general
- No undervoltage or overvoltage
- Engine running or drivetrain operational
- The rear end PRE-SAFE® function switched on over the "Driver Assistant" menu of the IC
- No trailer recognized (with code (550) Trailer hitch)
The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" or "Drivetrain operational" signal to the radar sensors control unit via the chassis CAN 2, the chassis gateway control unit and chassis FlexRay.
The status of the rear end PRE-SAFE® function is sent by the instrument cluster via the chassis CAN 2, the chassis gateway control unit and chassis FlexRay to the radar sensors control unit.
The trailer recognition status is sent by the trailer recognition control unit (for code (550) Trailer hitch) via the interior CAN, front SAM control unit, chassis CAN 1, the chassis gateway control unit and chassis FlexRay to the radar sensors control unit.
Rear end PRE-SAFE®, general
The rear end PRE-SAFE® function extends the preventative occupant protection in dangerous situations associated with the following traffic. The center rear bumper radar sensor detects the traffic activity behind the own vehicle. The radar sensors control unit uses the information from the center rear bumper radar sensor to determine the closing speed and the distance from the traffic to the rear. Various measures are introduced on this basis that may be able to reduce the consequences of an accident for the passengers.
The possible measures are shown in chronological order in the following graphic:
Shows model 218.3
The rear end PRE-SAFE® function consists of the following subfunctions:
- Function sequence for vehicle detection and warning about the traffic to the rear (Escalation level t 1 )
- Function sequence for preparing the vehicle for collision (escalation level t 2 )
- Function sequence for activating the occupant protection measures (escalation level t 3 )
- Function sequence for securing the vehicle after the collision (escalation level t 4 )
Function sequence for vehicle detection and warning about the traffic to the rear (Escalation level t 1 )
Impact in approx. t = 1.4 ms:
If an approaching vehicle is detected by the center rear bumper radar sensor and is deemed accident-critical by the radar sensors control unit, the driver of this following vehicle is warned by activating the rear hazard warning flasher function (without code (460) Canada version and without code (494) USA version).
The flashing frequency of the rear turn signal lights is f = 5 Hz.
For vehicles with code (460) Canada version or with code (494) USA version the traffic to the rear is not warned by the function rear end hazard warning flasher.
Technical implementation
The radar sensors control unit reads in the signals from the center rear bumper radar sensor via radar CAN 2, evaluates them and sends the request for outputting a warning via the chassis FlexRay, electronic ignition lock control unit and chassis CAN 1 to the front SAM control unit. This evaluates the incoming request and activates the function rear end hazard warning flasher.
Detailed information about actuation of the "rear end hazard warning flasher" function is available in the separate function description for the "exterior lights".
Additional function requirements for preparing the standing vehicle for collision (escalation level t 2 )
- Vehicle at rest
- A braking request is recognized by through actuation of the brake pedal or actuation of the parking brake or engaging the gear range "P"
- Braking request sent by the hold function or by DISTRONIC PLUS
The Electronic Stability Program control unit sends the status of the brake system to the radar sensors control unit via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.
The front SAM control unit directly detects the status of the parking brake indicator switch and transmits the status of the parking brake to the radar sensors control unit via the chassis CAN 1, the chassis gateway control unit and the chassis FlexRay.
The fully integrated transmission control unit transmits the signal concerning the engaged gear range to the radar sensors control unit via the drive train CAN, CDI control unit or ME-SFI [ME] control unit, chassis CAN 1, chassis gateway control unit and chassis FlexRay. The instrument cluster transmits the vehicle speed via chassis CAN 2, the chassis gateway control unit and chassis FlexRay to the radar sensors control unit.
Function sequence for preparing the vehicle for collision (escalation level t 2 )
Impact in approx. t = 600 ms:
If the radar sensors control unit registers no or only inadequate deceleration of the approaching vehicle via the closing speed, the vehicle is "braked hard" as a preventive measure by increasing the brake pressure. The hard braking on the one hand significantly reduces the occupant load (whiplash), while on the other hand serves the protection of other road users. Uncontrolled movements of the vehicle after a rear end collision, which can lead to subsequent collisions, are reduced (collision with a vehicle directly ahead, collisions with pedestrians or another road user in crossing situations).
Technical implementation
The radar sensors control unit transmits the braking request via chassis FlexRay, the chassis gateway control unit and chassis CAN 1 to the Electronic Stability Program control unit which then actuates the traction system hydraulic unit accordingly.
Function sequence for activating the occupant protection measures (escalation level t 3 )
Impact in approx. t = 100 to 50 ms:
If the radar sensors control unit calculates that it is likely that there will be an imminent rear end collision based on the closing speed of the vehicle closing in from the rear, preventative measures are instigated for occupant protection. The driver and the front passenger are held in position in their seat in order to optimize the protective effect of the conventional restraint equipment.
Technical implementation
The radar sensors control unit transmits the following information via chassis FlexRay, the chassis gateway control unit and chassis CAN 1 to the Electronic Stability Program control unit:
- Closing speed of the vehicle to the rear
- Time until the possible impact of the vehicle to the rear
- Deployment recommendation for the front reversible emergency tensioning retractors
The Electronic Stability Program control unit initiates PRE-SAFE® measures to provide protection to occupants.
Detailed information about activating the reversible emergency tensioning retractors can be found in the separate function description "PRE-SAFE®, function".
Function sequence for securing the vehicle after the collision (escalation level t 4 )
About. t = 2 s after the impact:
After a rear end collision the brake pressure is held for about t = 2 s.
After a rear-end collision, the rear-end PRE-SAFE® function is no longer available until it is activated using a diagnostic tester.
Technical implementation
The technical implementation of "Maintain brake pressure" corresponds to the technical implementation of the escalation level 2.
| Electrical function schematic for PRE-SAFE rear end | PE30.30-P-2061-97XAA | ||
| Overview of system components for driver assistance systems | GF54.00-P-9998FQM |