PRE-SAFE rear, function - GF30.30-P-0015CAM
MODEL 207.3/4 as of model year 2014 with CODE 253 (Rear impact warning and protection system)
Function requirements, general
- No undervoltage or overvoltage
- Engine running or drivetrain operational
- Rear end PRE-SAFE function in "Assistance" of instrument cluster switched on
- 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 1, 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 (for code (550) Trailer hitch) is sent by the trailer recognition control unit 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 system of the vehicle in the event of an imminent rear-end collision. To do this, the traffic area in the rear of the systems vehicle is monitored using the center rear bumper radar sensor. The radar sensors control unit uses the information of the center rear bumper radar sensor to analyze the closing speed and the distance from the vehicle in the rear. Based on this information, various measures are initiated that are designed to lessen the possible consequences of an accident for the passengers.
The possible measures are shown in chronological order in the following graphic:
Function sequence for the rear end PRE-SAFE
The rear end PRE-SAFE function consists of the following subfunctions:
- Function sequence for vehicle detection and warning of the vehicle in 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 of the vehicle in the rear (escalation level t 1 )
Impact in approx. t = 1400 ms:
If a vehicle is detected in the traffic area in the rear by the center rear bumper radar sensor and deemed accident-critical by the radar sensors control unit, the driver of the vehicle in the rear is at first warned by activating the rear turn signal lights (without code (460) Canada version and without code (494) USA version) on the vehicle.
In vehicles with code (460) Canada version and code (494) USA version, there is no warning of the traffic in the rear by the rear end PRE-SAFE function.
Technical implementation
The radar sensors control unit reads in the signals of the center rear bumper radar sensor over radar CAN 2.
The request for issuing a warning is provided by the radar sensors control unit. To do this, the radar sensors control unit sends a request to issue a warning to the front SAM control unit via the chassis FlexRay, the chassis gateway control unit and chassis CAN 1. This unit evaluates the incoming request from the radar sensors control unit and sets the clock frequency of the turn signal lights. The front SAM control unit transmits the signaling request to the rear SAM control unit via the interior CAN. The rear SAM control unit reacts by actuating the rear turn signal lights at the clock frequency set by the front SAM control unit of f = 3 to 5 Hz.
A detailed description of this function can be found in the separate description "Turn signal light actuation function".
Additional function requirements for preparing the standing vehicle for collision (escalation level t 2 )
- Vehicle at rest
- Brake request recognized by:
- Depressing the brake pedal or
- Operation of parking brake or
- Gear range "P" engaged
- Brake request sent by:
- Hold function or
- DISTRONIC PLUS
The status of the brake system and the parking brake is sent by the Electronic Stability Program control unit to the radar sensors control unit via chassis CAN 1, the chassis gateway control unit and the chassis FlexRay.
The front SAM control unit directly detects the status of the parking brake indicator switch and transmit the information about 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.
Function sequence for preparing the stationary 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 brake of the systems vehicle is "firmly applied" as a preventive measure by increasing the brake pressure. The purpose is to secure the vehicle to prevent it from accelerating in the forward direction as a result of a possible rear-end collision. The purpose of this measure is to prevent, among other things, that the vehicle is pushed onto a preceding vehicle or for example onto an intersection as a result of a possible rear-end collision. Additionally, these measures can prevent injuries in the area of the cervical vertebrae of the occupants, since the acceleration of the vehicle and thus that of the occupants is reduced.
Technical implementation
For this purpose, the radar sensors control unit transmits a brake request via the chassis FlexRay, chassis gateway control unit and chassis CAN 1 to the Electronic Stability Program control unit which then actuates the traction system hydraulic unit correspondingly.
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 a rear-end collision is probable using the closing speed of the vehicle in the rear, the front reversible emergency tensioning retractors and NECK-PRO are activated.
Technical implementation
To do this, the radar sensors control unit transmits the following information to the Electronic Stability Program control unit via the chassis FlexRay, chassis gateway control unit and chassis CAN 1:
- Closing speed of the vehicle in the rear
- Time until the possible impact of the vehicle in the rear
- Deployment recommendation for the front reversible emergency tensioning retractors and NECK-PRO
The Electronic Stability Program control unit reacts by transmitting a request via chassis CAN 1 to the front left reversible emergency tensioning retractors, the front right reversible emergency tensioning retractors and to the Supplemental Restraint System control unit.
The detailed descriptions for these functions are contained in the separate descriptions "PRE-SAFE function" (front activation reversible emergency tensioning retractor) and "Supplemental Restraint System (SRS) function" (triggering of NECK-PRO).
Function sequence for securing the vehicle after the collision (escalation level t 4 )
Approx. t = 2000 ms after impact:
After a rear-end collision, the brake pressure is maintained for approx. t = 2000 ms if the brake pressure had previously been increased (escalation level t2 ).
After a rear end collision has occurred and been detected, the rear-end PRE-SAFE function is no longer available until it is activated using the diagnostic tester.
Technical implementation
The technical implementation of "Maintain brake pressure" corresponds to the technical implementation of the escalation level t2
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| Electrical function schematic for PRE-SAFE rear end | PE30.30-P-2061-97EAA | ||
| Overview of system components for driver assistance systems | GF54.00-P-9998CAM |