Active Brake Assist, Function - GF30.30-P-0020RFM
Model 205
as of model year 2019
with code 239 (Active Distance Assist DISTRONIC)
Model 205
as of model year 2019
with code 258 (Active Brake Assist System)
Model 253 (except 253.99)
as of model year 2020
with code 239 (Active Distance Assist DISTRONIC)
Model 253 (except 253.99)
as of model year 2020
with code 258 (Active Brake Assist System)
Function requirements, general
- Active Brake Assist coded in electronic ignition lock control unit
- Active Brake Assist controller unit or DISTRONIC Distance-Pilot control unit coded correctly
- 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 "Powertrain operational" signal via drive train CAN to the powertrain control unit. The powertrain control unit forwards the signal via periphery CAN to the Active Brake Assist controller unit or via chassis FlexRay to the DISTRONIC Distance-Pilot control unit.
- Vehicle is not in backward movement
Active Brake Assist, general points
Depending on the equipment, the Active Brake Assist is controlled by the Active Brake Assist controller unit or the DISTRONIC Distance-Pilot control unit. The Active Brake Assist continuously checks the safe distance to the vehicle immediately in front, warns the driver optically and acoustically of potential collisions (e.g. rear-end collision) with other vehicles, thereby significantly reducing the risk of accident. In an imminent collision situation, the Active Brake Assist may initiate autonomous braking.
To do this, the Active Brake Assist controller unit or the DISTRONIC Distance-Pilot control unit evaluates the traffic situation in front of the vehicle, the route immediately in front as well as the driver activity and constantly determines the risk potential of a possible collision.
Corresponding warnings are output in a vehicle speed range from v = 7 km/h to 250 km/h. If the driver reacts to the warning tones and brakes, he/she is supported here by the Brake Assist. This calculates the required brake force amplification according to the situation.
Autonomous partial braking is also initiated if there is no reaction from the driver to the warnings. In this way a possible collision can be avoided or at least its consequences can be reduced.
The Active Brake Assist detects pedestrians, who are located in the danger zone in front of the vehicle, in a vehicle speed range from v = 7 km/h to 60 km/h. In these cases, too, the Active Brake Assist warns the driver in case of a risk of collision, and supports the driver in case the driver does not apply enough braking power. If there is no reaction from the driver, the system automatically initiates brake application. In order to reduce the speed even faster, the Assist brakes at the same time as the warning is issued when pedestrians step into the danger zone relatively late.
Release of the Active Brake Assist takes place manually over the operating level in the head unit. For navigation in the operating menu the following options are available:
- Except code 446 (Touchpad only), the navigation takes place with the Audio/COMAND control panel. The Audio/COMAND control panel sends the respective control signals via the telematics CAN to the head unit.
- With code 446 (Touchpad only) or code 448 (Touchpad), the navigation takes place with the Touchpad. The touchpad sends the relevant operation signals to the head unit via the telematics CAN.
- The navigation can occur with code 531 (COMAND APS) per voice control. The driver FSE microphone is directly read in by the head unit.
- The navigation can occur over the head unit finger navigation pad and the "Back" button on the steering wheel. The head unit finger navigation pad and the "Back" button transmit the relevant control signals via the steering wheel electronics, the steering wheel CAN, the steering column tube module control unit, the suspension FlexRay, the electronic ignition lock control unit and the user interface CAN to the head unit.
- The operating menu can be called up on the upper control panel control unit via the vehicle button. The status of the vehicle button is transmitted by the upper control panel control unit via the LCP-LIN, the touchpad (with code 446 (Touchpad only) or the Audio/COMAND control panel (except code 446 (Touchpad only)) and the telematics CAN to the head unit.
The head unit transmits the relevant status to the electronic ignition lock control unit via user interface CAN. The electronic ignition lock control unit forwards the status via periphery CAN to the Active Brake Assist controller unit or via chassis FlexRay to the DISTRONIC Distance-Pilot control unit.
The following components are integrated in the Active Brake Assist controller unit or in the DISTRONIC Distance-Pilot control unit:
- Radar sensor
- Control unit
with CODE 299 (PRE-SAFE® system)
The Active Brake Assist supports the PRE-SAFE® safety system.
The following presentation shows the detection range of the integral radar sensor:
Illustration of the principle of the detection range of the radar sensor, shown on model 205.0
The Active Brake Assist consists of the following subfunctions:
- Function sequence for distance warning
- Function sequence for brake force boosting
- Function sequence for autonomous brake application
- Function sequence for emergency braking in the case of pedestrians crossing in front of the vehicle
Function sequence for distance warning
Apart from data from the radar sensor, the Active Brake Assist controller unit or the DISTRONIC Distance-Pilot control unit evaluates the following variables:
- Direction of travel and vehicle speed
- Acceleration/yaw rate
- Steering wheel angle
- Driver activity:
- Accelerator pedal position
- Brake pedal position
- Setting the turn signal (turn signaling)
Direction of travel and vehicle speed:
The direction of travel is defined using the wheel rotation direction. The vehicle speed is calculated from the wheel speed. The Electronic Stability Program control unit sends appropriate information via chassis FlexRay, the electronic ignition lock control unit and periphery CAN to the Active Brake Assist controller unit, or via chassis FlexRay to the DISTRONIC Distance-Pilot control unit.
Acceleration/yaw rate:
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 appropriate values via vehicle dynamics CAN, Electronic Stability Program control unit, chassis FlexRay, electronic ignition lock control unit and periphery CAN to the Active Brake Assist controller unit or via vehicle dynamics CAN, Electronic Stability Program control unit and chassis FlexRay to the DISTRONIC Distance-Pilot control unit.
Steering wheel angle:
The steering wheel angle sensor detects/records the steering wheel angle. The steering column tube module control unit directly reads in the signals from the steering wheel angle sensor and sends them via the chassis FlexRay, electronic ignition lock control unit and periphery CAN to the Active Brake Assist controller unit, or via the chassis FlexRay to the DISTRONIC Distance-Pilot control unit. The data from the steering wheel angle sensor serve to test the plausibility of the yaw rate detected by the acceleration sensor.
Accelerator pedal position:
The powertrain control unit sends information on the accelerator pedal position via periphery CAN to the Active Brake Assist controller unit or via chassis FlexRay to the DISTRONIC Distance-Pilot control unit.
Brake pedal position:
The Electronic Stability Program control unit sends information about the position of the brake pedal via chassis FlexRay, electronic ignition lock control unit and periphery CAN to the Active Brake Assist controller unit or via chassis FlexRay to the DISTRONIC Distance-Pilot control unit.
Setting the turn signal (turn signaling):
The steering column tube module control unit reads in the switch position of the combination switch directly and sends this via chassis FlexRay, electronic ignition lock control unit and periphery CAN to the Active Brake Assist controller unit or via chassis FlexRay to the DISTRONIC Distance-Pilot control unit.
The Active Brake Assist controller unit or the DISTRONIC Distance-Pilot control unit calculates the distance to the obstacle and the time up to a possible collision. The Active Brake Assist controller unit or the DISTRONIC Distance-Pilot control unit differentiates here between a static distance warning (except code 460 (Canada version) and except code 494 (USA version)) and a collision-critical distance warning.
Static distance warning (without code 460 (Canada version) and without code 494 (USA version)):
Output of the static distance warning takes place purely optically.
If, in flowing traffic, the distance to the vehicle in front falls below t = 0.8 s and will remain for t > 3 s in this critical distance (e.g. at a speed of v = 100 km/h, distance approx. s = 22.2 m), the Active Brake Assist controller unit transmits the warning output request via the peripherals CAN or the Distance Pilot DISTRONIC control unit via the suspension FlexRay to the electronic ignition lock control unit. The electronic ignition lock control unit passes on the request via the user interface CAN to the instrument cluster, which then actuates the DISTRONIC warning indicator.
Collision critical distance warning:
Output of the collision-critical distance warning takes place optically and acoustically.
If an obstacle in the radar sensor detection range is classified as accident critical (collision within t < 2.6 s), the Active Brake Assist controller unit transits the warning output request via the peripherals CAN or the Distance Pilot DISTRONIC control unit via the suspension FlexRay to the electronic ignition lock control unit. The electronic ignition lock control unit forwards the request via the user interface CAN to the instrument cluster that then activates the DISTRONIC warning display and directly actuates the instrument cluster speaker (intermittent warning tone).
The warning output cannot be acknowledged. Take-back of the warning only occurs if the situation has been defused.
For output of the warning, the Active Brake Assist controller unit or the DISTRONIC Distance-Pilot control unit also takes the driver activity and the route directly ahead into account along with the vehicle speed and the distance to an obstacle. The vehicle moving directly ahead is detected through modifications of the accelerator pedal position, through actuation of the turn signal or through pressing the brake pedal. The route ahead is defined over the yaw rate, the steering wheel angle and the direction of travel.
The distance warning function can react up to a vehicle speed of v = 250 km/h to obstacles ahead or up to approx. v = 80 km/h to stationary obstacles (e.g stopping or parking vehicles).
The collision-critical warning is not output for the following events:
- Collisions with animals
- Collisions with oncoming vehicles
- Collisions with cross traffic
- Collisions in curves
Warning message in the instrument cluster
Function sequence for brake force boosting
If the driver reacts to the collision-critical distance warning with maximum full-stop braking, the Brake Assist provides support for the best possible utilization of the braking distance to the obstacle. The brake force boosting is available in a vehicle speed range from v ≥ 7 km/h to 250 km/h.
The Active Brake Assist controller unit or the DISTRONIC Distance-Pilot control unit evaluates the data from the radar sensor and permanently calculates the required brake force.
The emergency braking is defined over the actuation speed and the actuation strength with which the brake pedal is actuated.
The actuation speed and the actuation forces are detected by 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 transmits this information via the suspension FlexRay, electronic ignition lock control unit and peripherals CAN to the Active Brake Assist controller unit or via the suspension FlexRay to the Distance Pilot DISTRONIC controller unit.
In the event of maximum full-stop braking, the Active Brake Assist controller unit (via peripherals CAN, electronic ignition lock control unit and suspension FlexRay) or the Distance-Pilot DISTRONIC control unit (via the suspension FlexRay) transmits the request for the necessary brake force to the Electronic Stability Program control unit, which controls the hydraulic brake pressure via the traction system hydraulic unit. For vehicles with code 299 (PRE-SAFE® system) the PRE-SAFE® function implemented in the Electronic Stability Program control unit evaluates the currently requested braking torque and, if necessary, initiates appropriate measures.
If a collision is unavoidable, occupant protection measures are taken in addition to intervention by the brake system.
If there is no actuation or the intensity of actuation of the brake pedal by the driver considerably decreases, the brake boost on the driver braking is reduced and the Brake Assist System is also deactivated. The Brake Assist System will also be deactivated if the driver presses the accelerator pedal.
The Brake Assist can react to stationary obstacles up to a vehicle speed of approx. v = 80 km/h.
Additional function requirements for autonomous braking
- Vehicle speed: Approx. v = 7 to 250 km/h (to obstacles in front) or approx. v = 7 to 80 km/h (to stationary obstacles)
- Driver seat belt fastened
Function sequence for autonomous brake application
If the driver fails to react in an accident-critical situation to the warning, the Active Brake Assist controller unit or the DISTRONIC Distance-Pilot controller unit initiates autonomous braking and a reduction in engine torque. The Active Brake Assist controller unit or the Distance Pilot DISTRONIC control unit calculates the required braking torque (average deceleration approx. a = 6 m/s2 ) taking into account the following variables:
- Speed difference relative to the vehicle or obstacle
- Distance from vehicle or obstacle
The Active Brake Assist controller unit (via periphery CAN, electronic ignition lock control unit and chassis FlexRay), or the DISTRONIC Distance-Pilot controller unit (via chassis FlexRay) transmits the request to increase the braking torque and to reduce the engine torque to the Electronic Stability Program control unit. The Electronic Stability Program control unit evaluates the incoming requests, actuates the traction system hydraulic unit directly, and sends the request to reduce engine torque via the suspension FlexRay, powertrain control unit and the drive train CAN to the CDI control unit or the ME-SFI [ME] control unit.
If the driver reacts to the autonomous brake application and brakes, the Brake Assist provides support in order to make the best possible use of the braking distance to the obstacle.
If a collision is unavoidable, occupant protection measures are taken in addition to intervention by the brake system.
Additional function requirements for emergency braking in the case of pedestrians crossing in front of the vehicle
- Vehicle speed: Approx. v = 7 to 60 km/h
- Driver seat belt fastened
Function sequence for emergency braking in the case of pedestrians crossing in front of the vehicle
If the driver fails to react in an accident-critical situation to the warning, the Active Brake Assist controller unit or the DISTRONIC Distance-Pilot controller unit initiates autonomous braking and a reduction in engine torque. The Active Brake Assist controller unit or the Distance Pilot DISTRONIC control unit calculates the required braking torque (average deceleration approx. a = 6 m/s2 ) taking into account the following variables:
- Speed differential to the pedestrian
- Distance to the pedestrian
The Active Brake Assist controller unit (via periphery CAN, electronic ignition lock control unit and chassis FlexRay), or the DISTRONIC Distance-Pilot controller unit (via chassis FlexRay) transmits the request to increase the braking torque and to reduce the engine torque to the Electronic Stability Program control unit. The Electronic Stability Program control unit evaluates the incoming requests, actuates the traction system hydraulic unit directly, and sends the request to reduce engine torque via the suspension FlexRay, powertrain control unit and the drive train CAN to the CDI control unit or the ME-SFI [ME] control unit.
If the driver reacts to the autonomous brake application and brakes, the Brake Assist provides support in order to make the best possible use of the braking distance to the obstacle.
If a collision is unavoidable, occupant protection measures are taken in addition to intervention by the brake system.
| Electrical function schematic for Active Brake Assist | Model 205 as of model year 2019 with code 258 (Active Brake Assist System) | PE30.30-P-2070-97FBA | |
| Model 205 as of model year 2019 with code 239 (Active Distance Assist DISTRONIC) | PE30.30-P-2070-97FBB | ||
| Overview of system components for driver assistance systems | GF54.00-P-9998RFM |