PRE-SAFE brake, function - GF30.30-P-3340CAM
MODEL 207.3/4 as of model year 2014 with CODE 271 (Autonomous brake intervention/pedestrian protection) with CODE 300 (Collision mitigation (PRE-SAFE® Brake))
Function requirements, general
- No undervoltage or overvoltage
- "CMS_Avl" programmed in SAM control unit at the front
- Function PRE-SAFE® brake in the "Assistance" menu of the IC switched on
- Engine running or drivetrain operational
- Gear range "D" engaged (vehicle not in backward movement)
- Radar sensor system soiling and function test for the radar sensor system completed successfully
Object recording (e.g. vehicle ahead) via the radar sensor system is based on the radar measuring procedure. The front long range radar sensor and the DISTRONIC (DTR) sensors on the front bumper perform a soiling and function test after each engine start to securing perfect functioning. The function test requires an object in the respective detection area, and is used as a reference object. The Pre-SAFE brake cannot be activated if a malfunction is established or if there are no objects (for the function test) in the detection range of the radar sensor. The radar sensors control unit receives the signals from the DISTRONIC (DTR) sensors on the front bumper via the radar CAN 1 and sends them via the chassis FlexRay to the front long range radar sensor. The front long range radar sensor evaluates them in combination with its own signals and, when all the radar sensors are functioning correctly, sends the "Radar sensor system operational" status via chassis FlexRay to the radar sensors control unit.
- Stereo multifunction camera soiling and function test completed successfully
- Electronic Stability Program (ESP®) not switched to passive mode
- No active ESP® intervention recognized (vehicle not in sliding movement)
- Vehicle speed from v = 7 to 200 km/h
- Standstill control, enable issued (driver door/driver belt buckle and front passenger door closed)
The instrument cluster transmits the status of the PRE-SAFE® brake function via chassis CAN 2, front SAM control unit, chassis CAN 2, the chassis gateway control unit and chassis FlexRay to the radar sensors control unit.
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, chassis gateway control unit and chassis FlexRay.
The fully integrated transmission control unit transmits information about 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 Electronic Stability Program control unit transmits the status of the ESP® via the chassis CAN 1, chassis gateway control unit and chassis FlexRay to the radar sensors control unit.
The acceleration/yaw rate is detected by the yaw rate sensor for lateral and longitudinal acceleration. The yaw rate sensor for lateral and longitudinal acceleration transmits appropriate values via the dynamics CAN to the Electronic Stability Program control unit. The Electronic Stability Program control unit sends this via chassis CAN 1, chassis gateway control unit and chassis FlexRay to the video and radar sensors control unit.
The vehicle speed is calculated from the wheel speeds, the direction of travel is defined by the wheel rotation direction. The Electronic Stability Program control unit transmits information about the wheel speed and wheel rotation direction to the radar sensors control unit via chassis CAN 1, the chassis gateway control unit and chassis FlexRay.
PRE-SAFE® brake, general points
The PRE-SAFE® brake assesses the traffic situation in front of the vehicle and continuously determines the hazard potential for a rear-end collision. Dependent on factors such as the distance to a stationary or moving object, the relative speed to a vehicle immediately in front, as well as additional driving dynamic factors, a visual (static distance warning) and then a visual-acoustic warning (collision-critical distance warning) is issued. The distance warning is issued up to a speed of v = 250 km/h. In a collision-critical situation (driver fails to respond to the warning messages), first an autonomous partial and then emergency braking will be initiated to prevent a collision or to at least minimize its consequences. These interventions by the brake system by the PRE-SAFE® brake are possible in the vehicle speed range of v = 7 to 200 km/h. For stationary obstacles and pedestrians, the PRE-SAFE® brake is only activated if the own vehicle speed is a maximum of v = 72 km/h.
The PRE-SAFE® brake feature also supports the PRE-SAFE® safety concept. The function PRE-SAFE® is described in the separate function description "PRE-SAFE® function".
Following autonomous emergency braking until the point of vehicle standstill, the vehicle is locked stationary (stalled) for a time period of approx. t = 1 s.
Illustration of the principle of the PRE-SAFE® brake function for v ≥30 km/h
Function sequence for PRE-SAFE® brake
The PRE-SAFE® brake requires the following input factors to implement the distance warning and autonomous partial and emergency braking functions:
- Object recognition in the long range
- Object recognition in the short range
- Detection of stationary and slow-moving pedestrians (with code 271 (Autonomous intervention by the brake system/pedestrian protection)):
Detection ranges for radar sensor system/stereo multifunction camera, shown on model 212.0
Object recognition in the long range:
The front long range radar sensor monitors the area in front of the vehicle up to a distance of s = 200 m within a corridor of ∠ = 18°.
The front long range radar sensor operates according to the pulse modulated Doppler radar concept, which enables the distances and speeds of individual objects (e.g. vehicles) to be measured independently of each other.
The front long-range radar sensor sends corresponding information via the chassis FlexRay to the radar sensors control unit.
Object recognition in the short range:
Up to a distance of s = 30 m, objects are additionally detected by the front bumper DISTRONIC (DTR) radar sensors (short range radar sensor system). The object detection by the short range radar sensor system simply serves to allow plausibility checking.
The DISTRONIC (DTR) sensors on the front bumper transmit information via radar CAN 1 to the radar sensors control unit.
Detection of stationary and slow-moving pedestrians (for code 271 (Autonomous intervention by the brake system/pedestrian protection)): Pedestrians located in an area at the side of the lane can be detected in a vehicle speed range of v = to 72 km/h.
People are detected by the stereo multifunction camera, the front long range radar sensor and the front DISTRONIC (DTR) bumper sensors. The radar sensor system detects people or objects, and it can conduct positioning within a defined range - dependent on the distance from the person or object involved and the vehicle speed. It is not however capable of performing exact position finding in a transverse direction. This is why redundant detection by the stereo multifunction camera is required.
The stereo multifunction camera consists of two high-resolution mono cameras and an integrated control unit for evaluation and a plausibility check of the supplied picture data. The laterally offset location of the two mono cameras creates a difference in perspective (parallax displacement) between the left and right optical path. The distance to the detected object and other variables such as the height, size and circumference or the speed of motion can be evaluated on the basis of the differences between the image data.
The stereo multifunction camera sends the lane data via the chassis FlexRay to the radar sensors control unit.
Detailed information on safety precautions in the event of a collision with people is available in the separate "Supplemental Restraint System Function" function description in the "Pedestrian protection function" subfunction (for code U60 (Pedestrian protection)). If objects are detected on one's own lane by the radar sensor system or by the stereo MFK (vehicle speed range of v = 7 to 200 km/h), the radar sensors control unit outputs a static or a collision-critical distance warning.
Static distance warning:
Output of the static distance warning takes place purely optically. The static distance warning is triggered at a vehicle speed v > 30 km/h, if the time interval between the vehicle and the vehicle driving immediately ahead is less than t = 0.8 s (e.g. in moving traffic). The DISTRONIC warning lamp lights up in the IC.
To do this, the radar sensors control unit sends the appropriate request via the chassis FlexRay, the chassis gateway control unit, chassis CAN 1, front SAM control unit and chassis CAN 2 to the IC. Collision critical distance warning:
Output of the collision-critical distance warning takes place optically and acoustically.
If a moving or stationary obstacle is classified as accident-critical in the detection range of the radar sensor system at a vehicle speed of v > 7 km/h, the DISTRONIC warning lamp lights up and the instrument cluster speaker emits an intermittent tone.
The warning is switched off again automatically one the situation is no longer critical.
To do this, the radar sensors control unit sends the appropriate request via the chassis FlexRay, the chassis gateway control unit, chassis CAN 1, front SAM control unit and chassis CAN 2 to the IC. The instrument cluster actuates the warning buzzer directly.
Optical warning messages in instrument cluster
This is shown inversely on the multifunction display, i.e. the distance warning readiness indicator is hidden when the distance warning function is active. If the distance warning function is deactivated, the distance warning readiness indicator and the "OFF" lettering are shown.
If the driver does not react to the warnings, the PRE-SAFE® brake initiates autonomous partial braking. To do this the radar sensors control unit calculates a corresponding braking torque while taking account of the driving dynamics input factors.
The radar sensors control unit sends the corresponding request via the chassis FlexRay, chassis gateway control unit and chassis CAN 1 to the Electronic Stability Program control unit, which then directly actuates the traction system hydraulic unit.
The Electronic Stability Program control unit determines the braking desire of the driver via the increasing brake pressure in the master brake cylinder. The brake pressure is registered by the front axle brake pressure sensor. The Electronic Stability Program control unit reads in the signals of the front axle brake pressure sensor directly, calculates the braking torque requested by the driver and transmits this information via chassis CAN 1, the chassis gateway control unit and chassis FlexRay to the radar sensors control unit.
If the driver fails to respond to partial braking (evasive maneuver, BAS-PLUS-assisted emergency braking), the radar sensors control unit initiates emergency braking to avoid a collision or to reduce the consequences of an accident.
Detailed information about BAS PLUS is available in the separate "BAS PLUS function" subfunction.
Emergency braking is only triggered if the driver and the front passenger have their seat belts on.
Parallel to this the function PRE-SAFE® integrated into the Electronic Stability Program control unit evaluates the current requested braking torque and instigates appropriate measures as necessary. Detailed information on the occupant protection system is available in the separate function description for the "PRE-SAFE® function".
| Electrical function schematic for PRE-SAFE brake | PE30.30-P-2060-97EAA | ||
| Overview of system components for driver assistance systems | GF54.00-P-9998CAM |