Rear Pre-Safe (R), Function - GF30.30-P-0015FR
Model 257, 290
up to model year 2021
with code 23P (Drive package)
Model 257, 290
up to model year 2021
with code P20 (Driving assistant package Plus)
Shown on models 257, 290
Function requirements, general
- No undervoltage or overvoltage
- Engine running or drivetrain operational:
The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" or "Drivetrain operational" signal to the Mercedes-Benz Intelligent
The possible measures are shown in chronological order in the following graphic:
Drive control unit via drive CAN, powertrain control unit and suspension FlexRay.
- No trailer recognized (with CODE 550 (Trailer hitch))
The trailer recognition control unit (with code 550 (trailer hitch)) sends the "trailer recognized" status via the interior CAN, electronic ignition lock control unit, and suspension FlexRay to the Mercedes-Benz Intelligent Drive control unit.
Rear end PRE-SAFE®, general
The rear end PRE-SAFE® function extends the preventative occupant protection system in dangerous situations associated with following traffic. The rear bumper radar sensor on the outer right and left detect the traffic behind one's own vehicle. The Mercedes-Benz Intelligent Drive control unit analyzes the information provided by the rear bumper radar sensors on the outer right and left to determine the closing speed of and distance to the following traffic. Various measures are introduced on this basis that may be able to reduce the consequences of an accident for the vehicle occupants.
Shown on model 257
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 t1)
- Function sequence for preparing the stationary vehicle for a collision (escalation level t2)
- Function sequence for activating the occupant protection measures (escalation level t3)
- Function sequence for securing the vehicle after the collision (escalation level t4)
Function sequence for vehicle detection and warning about the traffic to the rear (Escalation level t1)
Impact in approx. t = 1, 4 s:
If an approaching vehicle is detected by the left and right outer rear bumper radar sensors and classified as accident critical by the Mercedes-Benz Intelligent Drive control unit, the driver of this following vehicle is warned via the output of the rear hazard warning flasher function (except code 494 (USA version) and except code 460 (Canada version)).
The flashing frequency of the rear turn signal indicator is f = 5 Hz.
Technical implementation
The Mercedes-Benz Intelligent Drive control unit reads in the signals of the left and right outer rear bumper radar sensors via the rear radar CAN, evaluates these and transmits the warning output request via the suspension FlexRay, electronic ignition lock control unit and interior CAN to the front SAM control unit (except code 494 (USA version) and except code 460 (Canada version)). This evaluates the incoming request and activates the function rear end hazard warning flasher.
Additional function requirements for preparing the standing vehicle for a collision (escalation level t2)
- Vehicle at a standstill:
- Brake request detected by actuating the brake pedal or actuating the parking brake or by engaging gear range "P"
The Electronic Stability Program control unit sends the status of the braking system via the suspension FlexRay to the Mercedes-Benz Intelligent Drive control unit.
The Electronic Stability Program control unit activates the parking brake, reads the status of the electric parking brake switch in directly, and sends this to the Mercedes-Benz Intelligent Drive control unit via the suspension FlexRay.
The fully-integrated transmission control electric controller unit control unit sends information about the selected drive range via drive CAN, powertrain control unit and suspension FlexRay to the Mercedes-Benz Intelligent Drive control unit.
- The brake request is transmitted from the hold function or the DISTRONIC interval pilot (with code 23P (Driver Assist Package Plus))
- Brake request detected by actuating the brake pedal or actuating the parking brake or by engaging gear range "P"
- The vehicle is braked to a standstill by the DISTRONIC interval pilot (with code 23P (Driver Assist Package Plus))
The Electronic Stability Program control unit calculates the vehicle speed from the wheel speed signals, and sends this to the Mercedes-Benz Intelligent Drive control unit via the suspension FlexRay.
Function sequence for preparing the stationary vehicle for a collision (escalation level t2)
Impact in approx. t = 300 s:
If the Mercedes-Benz Intelligent Drive control unit registers none or only inadequate deceleration of the approaching vehicle via the closing speed, the vehicle is "stalled" by increasing the brake pressure as a preventive measure. 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 that could lead to subsequent collisions are minimized (collision with a vehicle in front, collisions with pedestrians or other road users in situations involving an intersection).
Technical implementation
The Intelligent Drive control unit sends the brake request via the suspension FlexRay 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 t3)
Impact in approx. t = 100 - 50 ms:
If the Mercedes-Benz Intelligent Drive control unit 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 their seat in order to optimize the protective effect of the conventional restraint equipment.
Technical implementation
The Mercedes-Benz Intelligent Drive 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
The Electronic Stability Program control unit initiates PRE-SAFE® measures to provide protection to occupants.
Function sequence for securing the vehicle after the collision (escalation level t4)
After a rear-end collision the rear end PRE-SAFE® function is no longer available until it is activated using a diagnostic tester.
About t = 2 s after an impact:
Brake pressure continues to be applied for approx. t = 2 s after a rear-end collision.
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-2061-97XBA | ||
| Overview of system components for driver assistance systems | GF54.00-P-9998FR |