PRE-SAFE rear, function - GF30.30-P-0015GN
MODEL 166 as of model year 2016 with CODE 253 (Rear impact warning and protection system)
MODEL 292 with CODE 253 (Rear impact warning and protection system)
Block diagram, except model 166.063
Block diagram, model 166.063
Function requirements, general
- No undervoltage or overvoltage
- Engine running or drivetrain operational
- No trailer recognized (with CODE 550 (Trailer hitch)) (except model 166.063)
(Except model 166.063) The CDI control unit or ME-SFI [ME] control unit sends the "engine running" or "drivetrain operational" signal via chassis CAN 1, chassis gateway control unit (with CODE 23P
(Driving assistance package Plus)), and chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package Plus)).
(Model 166.063) The ME-SFI [ME] control unit sends the "engine running" or "drivetrain operational" signal via engine CAN, powertrain control unit, chassis CAN 1, chassis gateway control unit (with CODE 23P (Driving assistance package Plus)), and chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package Plus)).
The instrument cluster transmits the status of the rear PRE-SAFE function via chassis CAN 2, the electronic ignition lock control unit, chassis CAN 1, the chassis gateway control unit (with CODE 23P (Driving assistance package Plus)) and chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package Plus)).
The trailer recognition control unit (with CODE 550 (trailer hitch)) (except model 166.063) transmits the status "Trailer detected" via interior CAN, electronic ignition lock control unit, chassis CAN 1, chassis gateway control unit (with CODE 23P (Driving assistance package Plus)) and chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package Plus)).
Rear end PRE-SAFE, general
The function PRE-SAFE rear end extends the preventative occupant protection in dangerous situations through the traffic to the rear. The rear center bumper radar sensor detects the traffic occurring behind one's own vehicle. The radar sensors control unit (with CODE 23P (Driving assistance package Plus)) analyzes the information provided by the center rear bumper radar sensor to determine the closing speed and the distance to following traffic. 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:
Shown: Model 292
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 t1)
Impact in approx. t = 1.4 ms:
Applies at a speed of v >/= 30 km/h. Below 30 km/h, t is linear to the speed e.g. at 15 km/h t is = 0.7 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 (with CODE 23P (Driving assistance package Plus)), 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 indicator is f = 5 Hz.
On vehicles with CODE 460 (Canada version) or CODE 494 (USA version), following traffic is not warned by the rear hazard warning flasher function.
Technical implementation
The radar sensors control unit (with CODE 23P (Driving assistance package Plus)) reads the signals of the center rear bumper radar sensor via radar CAN 2, evaluates these signals and transmits the request to issue a warning via chassis FlexRay, chassis gateway control unit (with CODE 23P (Driving assistance package Plus)), chassis CAN 1, electronic ignition lock control unit and interior CAN to the 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 a collision (Escalation level t 2 )
- Vehicle at rest
- Rear-end collision impending
- Brake request detected by actuating the brake pedal or parking brake, or by engaging gear range "P"
- Brake request transmitted by the HOLD function, or transmitted by DISTRONIC PLUS with Steer Assist and Stop & Go Pilot
Function sequence for preparing the vehicle for collision (Escalation level t2)
Impact in approx. t = 300 ms:
If the radar sensors control unit (with CODE 23P (Driving assistance package Plus) registers no or only inadequate deceleration of the approaching vehicle via the closing speed, the vehicle is "firmly braked" by increasing the brake pressure as a preventive measure. This firm braking considerably reduces the occupant load (whiplash) and provides protection to occupants of other vehicles in front that are involved in the accident. 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 (with CODE 23P (Driving assistance package Plus)) transmits the brake request via chassis FlexRay, chassis gateway control unit (with CODE 23P (Driving assistance package Plus)) 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 = 150 ms:
If the radar sensors control unit (with CODE 23P (Driving assistance package Plus) calculates that a rear-end collision is probable using the closing speed of the approaching vehicle, preventive measures designed to provide protection to occupants are initiated. The driver and the front passenger are held in position in order to optimize the protective effect of the conventional restraint equipment.
Technical implementation
The radar sensors control unit (with CODE 23P (Driving assistance package Plus)) transmits the following information via chassis FlexRay, chassis gateway control unit (with CODE 23P (Driving assistance package plus)) 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 starts PRE-SAFE measures for occupant protection.
Detailed information about activation of the reversible emergency tensioning retractor is available in the separate function description "PRE-SAFE function".
Function sequence for securing the vehicle after the collision (Escalation level t)
The occupant protection measures are aborted if the accelerator pedal is actuated or gear range "D" or "R" is engaged, or if DISTRONIC PLUS is automatically started with Steer Assist and Stop & Go Pilot, or the situation has gotten less critical.
The Electronic Stability Program control unit transmits the status of the brake system via chassis CAN 1, the chassis gateway control unit (with CODE 23P (Driving assistance package Plus)) and chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package Plus)).
The Electronic Stability Program control unit activates the electric parking brake and transmits the status of the electric parking brake switch via chassis CAN 1, the chassis gateway control unit (with CODE 23P (Driving assistance package Plus)) and chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package Plus)).
The fully integrated transmission control unit sends information about the gear range engaged via:
(Except model 166.063) drive train CAN, the CDI control unit or ME-SFI [ME] control unit, chassis CAN 1, the chassis gateway control unit (with CODE 23P (Driving assistance package Plus)) and chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package Plus)).
(Model 166.063) drive train CAN, the powertrain control unit, chassis CAN 1, the chassis gateway control unit (with CODE 23P (Driving assistance package Plus)) and chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package Plus)). The Electronic Stability Program control unit transmits the vehicle speed via chassis CAN 1, the chassis gateway control unit (with CODE 23P (Driving assistance package Plus)) and chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package Plus)).
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 unit.
Technical implementation
The technical implementation of "Maintain brake pressure" corresponds to the technical implementation of the Escalation level t 2
.
| Electrical function schematic for PRE-SAFE rear end | PE30.30-P-2061-97NBA |
| Overview of system components for driver assistance systems | GF54.00-P-9998GN |