PRE-SAFE brake, function - GF30.30-P-3340RF
Model 205, 253 with code 271 (Autonomous brake intervention/pedestrian protection)
Model 205, 253 with code 300 (PRE-SAFE® Brake)
Function requirements, general
- No undervoltage or overvoltage
- "BasExtd_Avl" (with code 268 (Brake Assist PLUS)) programmed in electronic ignition lock control unit
- "CMS_Avl" programmed in electronic ignition lock control unit
- PRE-SAFE® brake in "Driving Assist" of instrument cluster 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 front bumper radar sensors run a contamination and function test after each engine start to ensure that they are functioning correctly. The function test requires an object in the respective detection area, and is used as a reference object. If a malfunction is established or if there are no objects in the detection area, the PRE-SAFE® brake cannot be activated. The radar sensors control unit receives the signals of the front bumper radar sensors via the radar-CAN 1 and sends them over 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.
- Soiling and function test for the stereo MFK
- 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 status of the PRE-SAFE® brake function is sent by the instrument cluster via the user interface CAN, electronic ignition lock control unit and the 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 drive train CAN, powertrain control unit and chassis FlexRay.
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 Electronic Stability Program control unit sends the status of the Electronic Stability Program® via the suspension FlexRay to the radar sensors control unit.
The acceleration/yaw rate is detected by the acceleration sensor integrated into the Supplemental Restraint System control unit. The supplemental restraint system control unit sends the corresponding values via the vehicle dynamics CAN to the Electronic Stability Program control unit. The Electronic Stability Program control unit transmits these via the suspension FlexRay to the 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 sends this information about wheel speed and wheel rotation direction to the radar sensors control unit via 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 takes place up to a speed of v = 250 km/h. In a collision-critical situation in which the driver fails to respond to the warning messages, an autonomous partial brake application is performed followed later by emergency braking to avoid a collision or at least to minimize the consequences of a collision. For stationary obstacles and pedestrians the PRE-SAFE® brake is only activated if one's own vehicle speed is a maximum of v = 72 km/h.
The PRE-SAFE® brake feature also supports the PRE-SAFE® safety concept.
Illustration of the principle of the PRE-SAFE® brake function for v ≥ 30 km/h, shown on model 205.0
Following autonomous emergency braking until the point of vehicle standstill, the vehicle is locked stationary for a time period of t = 1 s.
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
- Object detection of stationary and slow moving pedestrians by the stereo multifunction camera (with code 271 (Autonomous intervention by the brake system/pedestrian protection))
Detection ranges for radar sensor system/stereo multifunction camera, shown on model 205.0
Object recognition in the long range:
The front long range radar sensor monitors the traffic area in front of the vehicle up to a distance of s = 200 m within a corridor of a = 18°. Objects up to a distance of s = 0 to 60 m are detected in a corridor of a = 60°.
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:
From a distance of s = 30 m object detection is also performed by the front bumper radar sensors (short range radar sensor system). The object detection by the short range radar sensor system simply serves to allow plausibility checking.
The front bumper radar sensors send information via the radar CAN 1 to the radar sensors control unit.
Detection of stationary and slow-moving pedestrians (with 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 bumper radar 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 positioning in the 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 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 object ahead and other variables such as the height, sized and scope or the speed of movement thereof are calculated 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.
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.
The radar sensors control unit sends the corresponding request via the chassis FlexRay, electronic ignition lock control unit and the user interface CAN to the instrument cluster.
Collision critical distance warning:
Output of the collision-critical distance warning takes place optically and acoustically.
At a vehicle speed of v > 7 km/h (v > mph), if a moving or stationary obstacle in the detection range is classified as accident critical by the radar sensor system, 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.
The radar sensors control unit sends a corresponding request to actuate the instrument cluster speaker via the chassis FlexRay, electronic ignition lock control unit and the user interface CAN to the instrument cluster. The instrument cluster directly actuates the instrument cluster speaker.
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 suspension FlexRay to the Electronic Stability Program control unit which then directly actuates the traction system hydraulic unit.
If the driver responds with emergency braking, BAS PLUS is activated. This supports the driver during emergency braking to make optimum use of the braking distance to the obstacle.
The Electronic Stability Program control unit the braking request of the driver about 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 directly reads in the signal from the front axle brake pressure sensor, calculates the braking torque requested by the driver and sends this information via the chassis FlexRay to the radar sensors control unit.
Model 205.012/047/147/212/247
with code 271 (Autonomous brake intervention/pedestrian protection) Model 205.012/047/147/212/247
with code 300 (PRE-SAFE® Brake)
The kinetic energy is converted within defined limits into electrical energy (regenerative braking). If the requested braking torque exceeds the deceleration through recuperation (for example in a case of a emergency braking), the Electronic Stability Program control unit additionally actuates the traction system hydraulic unit and therefore the service brake.
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.
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.
| Electrical function schematic for PRE-SAFE® brake | PE30.30-P-2060-97FBA |
| Overview of system components for driver assistance systems | GF54.00-P-9998RF |