Rear PRE-SAFE (R), Function - GF30.30-P-0015LF
Model 217, 222
up to model year 2018
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 drive train CAN, powertrain control unit and chassis FlexRay.
The status of the rear end PRE-SAFE function is sent by the instrument cluster via the user interface CAN, electronic ignition lock control unit and the suspension FlexRay to the radar sensors control unit.
Trailer recognition control unit (with code 550 (Trailer hitch)) transmits trailer status to radar sensors control unit via interior CAN, electronic ignition lock control unit and suspension FlexRay.
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 vehicle occupants.
The possible measures are shown in chronological order in the following graphic:
Shown model 222.0
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 s:
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 through output of the rear hazard warning flashing function (without code 460 (Canada version) and without code 494 (USA version)).
On vehicles with CODE 460 (Canada version) or CODE 494 (USA version), following traffic is not warned by the rear end hazard warning flasher function.
Technical implementation
The radar sensors control unit reads in the signals from the center rear bumper radar sensor via radar CAN 2, evaluates these and transmits the request to output a warning via the suspension FlexRay, electronic ignition lock control unit and interior CAN to the front SAM control unit. This evaluates the incoming request and activates the function rear end hazard warning flasher.
Detailed information for actuation of the rear end hazard warning flasher function is available in a separate document.
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 braking system via the chassis FlexRay to the radar sensors control unit.
The electric parking brake control unit transmits the status of the parking brake via the periphery CAN, electronic ignition lock control unit and chassis FlexRay to the radar sensors control unit.
The fully integrated transmission control unit sends information about the selected gear range via drive train CAN, powertrain control unit and suspension FlexRay to the radar sensors control unit.
The IC transmits the vehicle speed via the user interface CAN, electronic ignition lock control unit and suspension 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 sends the braking request via the suspension FlexRay to the Electronic Stability Program control unit which then directly actuates the traction system hydraulic unit appropriately.
Function sequence for activating the occupant protection measures (escalation level t 3 )
Impact in approx. t = 100 - 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 vehicle occupants are held in place in the seats in order to optimize the protective effect of the conventional restraint equipment.
Technical implementation
The radar sensors control unit transmits the following information via the suspension FlexRay 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
- Triggering recommendation for rear reversible emergency tensioning retractors (with code 305 (Rear PRE-SAFE))
The Electronic Stability Program control unit initiates PRE-SAFE measures to provide protection to occupants.
Detailed information about activation of the reversible emergency tensioning retractors is contained in a separate document.
Function sequence for securing the vehicle after the collision (escalation level t 4 )
About t = 2 s after an impact:
Brake pressure continues to be applied for approx. t = 2 s after a rear-end collision.
After a rear end collision the PRE-SAFE rear end function is no longer available until activation over a diagnostic tester.
Technical implementation
The technical implementation of "Maintain brake pressure" corresponds to the technical implementation of the escalation level t2
.
| Electrical function schematic for PRE-SAFE rear end | PE30.30-P-2061-97SEA | ||
| Overview of system components for driver assistance systems | GF54.00-P-9998LF |