Pre-Safe Brake, Function - GF30.30-P-3340GN

MODEL 166 as of model year 2016 with CODE 271 (Autonomous brake intervention/pedestrian protection) with CODE 300 (PRE-SAFE® Brake) 

MODEL 292 with CODE 271 (Autonomous brake intervention/pedestrian protection) with CODE 300 (PRE-SAFE® Brake) 

Block diagram, except model 166.063 

Block diagram, model 166.063 

Function requirements, general 

• No undervoltage or overvoltage
• "CMS_Avl" programmed in electronic ignition lock control unit
• "BasExtd_Avl" (with CODE (268) Brake Assist PLUS) programmed in electronic ignition lock control unit
• PRE-SAFE® brake in "Driving Assistance" menu of instrument cluster switched on
• Engine running or drivetrain operational
• Gear range "D" engaged (vehicle not in backward movement)
• Vehicle speed from v = 7 to 200 km/h
• Driver and front passenger belt buckle latched (if front passenger detected by seat recognition)

If a front passenger is detected, the weight sensing system (WSS) control unit sends the status of the seat recognition via the seat occupied recognition LIN, supplemental restraint system control unit, and chassis CAN1 to the Electronic Stability Program control unit. The Electronic Stability Program control unit needs this information to determine the braking torque.

• 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 which is used as a reference value. 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 (with CODE 23P (Driving assistance package plus)) receives the signals from the front bumper radar sensors via radar CAN 1 and sends them via 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 the chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package plus)).

• ESP® not switched to passive (except AMG models)
• ESP® not switched to "SPORT HANDLING MODE" (with AMG)
• No active ESP® intervention recognized (vehicle not in sliding movement)
• Standstill control, enable issued (driver door and front passenger door closed)

The status of the PRE-SAFE® brake function is sent by the instrument cluster via the chassis CAN 2, 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)).

The CDI control unit or ME-SFI [ME] control unit sends the "engine running" or "drivetrain operational" signal via the 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 ME-SFI [ME] control unit sends the "engine running" or "drivetrain operational" signal via the 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 fully integrated transmission control unit sends information about the gear range engaged via the drive train CAN, CDI control unit or ME-SFI [ME] control unit, or on model 166.063, via the 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 Electronic Stability Program control unit sends the status of the ESP® 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)). The acceleration/turn rate is detected by the yaw rate sensor for lateral and longitudinal acceleration. The turn 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 information via the 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 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 information about the wheel speed and wheel rotation direction via the 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)).

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. Depending on factors such as the distance to a stationary or moving object, the relative speed to a vehicle in front, and driving dynamic factors, a visual warning (static distance warning) is issued when the distance is too small or a visual-acoustic warning (collision-critical distance warning) is issued during collision-critical situations. In a collision-critical situation (driver fails to respond to warning messages) autonomous partial braking first takes place, followed by emergency braking to avoid a collision or at least minimize the consequences of a collision. These interventions by the brake system by the PRE-SAFE® brake are possible in the vehicle speed range of v = 7 up 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

Illustration of the principle of the PRE-SAFE® brake function for v 30 km/h, shown on model 292 

After autonomous emergency braking until the vehicle reaches a 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
• 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 (with CODE 23P (Driving assistance package plus)), shown on model 292 

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°. Objects up to a distance of s = 0 to 60 m are detected in a corridor of ∠ = 60°.

The front long range radar sensor sends corresponding signals via the chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package plus)).

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 (with CODE 23P (Driving assistance package plus)). 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). Object detection by the short range radar sensor system is merely used for the plausibility check.

The front bumper radar sensors send information via the radar CAN 1 to the radar sensors control unit (with CODE 23P (Driving assistance package plus)).

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.

The stereo multifunction camera (with CODE 23P (Driving assistance package plus)) consists of two high-resolution mono cameras and an integrated control unit for evaluation and plausibility check of the picture data provided. 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 (with CODE 23P (Driving assistance package plus)) sends corresponding data via the chassis FlexRay to the radar sensors control unit (with CODE 23P (Driving assistance package plus)).

Detailed information on safety precautions in the event of a collision with people is available in the separate function description "Supplemental Restraint System function" in the subfunction "Pedestrian protection function" (with CODE U60 (Active engine hood (pedestrian protection))).

If the radar sensor system or stereo multifunction camera (with CODE 23P (Driving assistance package plus)) detects objects in the driver's own lane (vehicle speed range of v = 7 to 200 km/h), the radar sensors control unit (with CODE 23P (Driving assistance package plus)) issues a static or 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.

People are detected by the stereo multifunction camera (with CODE 23P (Driving assistance package plus)), 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 position finding in a transverse direction. This is why redundant detection by the stereo multifunction camera (with CODE 23P (Driving assistance package plus)) is required.

The radar sensors control unit (with CODE 23P (Driving assistance package plus)) sends the corresponding request via the chassis FlexRay, chassis gateway control unit (with CODE 23P (Driving assistance package plus)), chassis CAN 1, electronic ignition lock control unit, and chassis CAN 2 to the instrument cluster.

Collision critical distance warning:

Output of the collision-critical distance warning takes place optically and acoustically.

If a moving or stationary obstacle in the detection range of the radar sensor system is classified as accident-critical at a vehicle speed of v > 7 km/h, the DISTRONIC warning lamp lights up and the warning buzzer in the instrument cluster emits an intermittent tone.

The warning is automatically deactivated again when the situation is no longer critical, and cannot be acknowledged while control is active.

The radar sensors control unit (for CODE 23P (Driving assistance package plus)) sends the corresponding request for actuating the instrument cluster warning buzzer via the chassis FlexRay, chassis gateway control unit (with CODE 23P (Driving assistance package plus)), chassis CAN 1, electronic ignition lock control unit, and chassis CAN 2 to the instrument cluster. 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 (with CODE 23P (Driving assistance package plus)) calculates the corresponding braking torque while taking account of the driving dynamics input factors.

The radar sensors control unit (with CODE 23P (Driving assistance package plus)) sends the corresponding request via the 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 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 signals from the front axle brake pressure sensor, calculates the braking torque requested by the driver, and sends this information via the 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)).

A detailed information about the BAS PLUS is available in the separate "BAS PLUS Function" partial function.

In model 166.063, the kinetic energy is converted into electrical energy via a generator (regenerative braking) within defined limits. 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 (for CODE 23P (Driving assistance package plus)) initiates emergency braking for max. 1 s to avoid a collision or minimize the consequences of an accident.

Emergency braking is not triggered if the front passenger seat is occupied and the front passenger is not strapped in.

Parallel to this, the PRE-SAFE® function integrated into the Electronic Stability Program control unit evaluates the currently requested braking torque and initiates appropriate measures for occupant protection as necessary.