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Active Brake Assist, Function - GF30.30-P-0020GWM

Model 463 (except 463.342) 

as of model year 2019 

G13657895Courtesy of MERCEDES-BENZ USA

Function requirements, general 

Active Brake Assist, general points 

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.

Respective warnings are issued in a vehicle speed range of v = 7 km/h to 250 km/h. If the driver reacts to the warnings and brakes, he is supported 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 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 initially warns the driver in the event of a risk of collision and supports him/her if he/she does not apply enough braking power. If there is no reaction from the driver, the system automatically initiates brake application. To be able to reduce speed even more quickly, the Assist already brakes at the same time that the warning is issued in the case of pedestrians (who step into the danger zone relatively late).

For object recognition, and for recognizing pedestrians in particular, the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit is supported by the mono multifunction camera. The mono multifunction camera sends its data via the suspension FlexRay to the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit. The evaluation of the data (data fusion) is carried out by the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit.

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:

The head unit sends the corresponding status via the user interface CAN, electronic ignition lock control unit, and suspension FlexRay to the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit.

The following component parts are integrated in the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit:

IMPORTANT The Active Brake Assist supports the PRE-SAFE® safety system. The following presentation shows the detection range of the integral radar sensor:

G13657896Courtesy of MERCEDES-BENZ USA

Illustration of the principle of the detection range of the radar sensor, shown on model 463 

The Active Brake Assist consists of the following subfunctions:

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: 

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 the appropriate information via suspension FlexRay to the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller 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 the vehicle dynamics CAN, Electronic Stability Program control unit, and suspension FlexRay to the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit.

Steering wheel angle: 

The steering wheel angle sensor detects/records the steering wheel angle. The steering column tube module control unit reads in the signals of the steering wheel angle sensor directly and sends information about the steering wheel angle via suspension FlexRay to the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller 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 about the accelerator pedal position via suspension FlexRay to the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit.

Brake pedal position: 

The Electronic Stability Program control unit sends information about the position of the brake pedal via suspension FlexRay to the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller 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 it via suspension FlexRay to the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller 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 Distance Pilot DISTRONIC controller unit differentiates here between a static (except code ZU8 (national version USA)) and a collision-critical distance warning.

Static distance warning (except code ZU8 (national version USA): 

Output of the static distance warning takes place purely optically. If, in moving traffic, the distance to the vehicle directly ahead becomes less than t = 0.8 s and this critical distance is maintained for t > 3 s (e.g at a speed of v = 100 km/h, distance approx. s = 22.2 m), the Active Brake Assist controller unit or Distance Pilot DISTRONIC controller unit sends the request to output the warning via suspension FlexRay, the electronic ignition lock control unit, and user interface CAN to the instrument cluster. The instrument cluster reacts by actuating 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 detection range of the radar sensor is classified as accident-critical (collision will occur within t < 2.6 s), the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit sends the request to output the warning via suspension FlexRay, the electronic ignition lock control unit, and user interface CAN to the instrument cluster, which then activates the DISTRONIC warning display and directly actuates the instrument cluster speaker (intermittent 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 via the yaw rate, the steering wheel angle, and the direction of travel.

The AWF can react up to a vehicle speed of v = 250 km/h to the obstacles directly ahead or up to about v = 70 km/h to the stationary obstacles, e.g. stopping or parking vehicles.

The collisions critical warning is not issued for a collision:

G13657897Courtesy of MERCEDES-BENZ USA

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 to make best possible use of the braking distance up to the obstacle. The brake force boosting is available in a vehicle speed range between v ≥ 7 km/h and 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.

IMPORTANT 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 master brake cylinder brake pressure sensor. The Electronic Stability Program control unit reads in the signals of the master brake cylinder pressure sensor directly, calculates the braking torque requested by the driver, and sends this information via suspension FlexRay to the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit.

In the event of maximum full-stop braking, the Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit sends the necessary brake force via suspension FlexRay to the Electronic Stability Program control unit, which actuates the hydraulic brake pressure via the traction system hydraulic unit. At the same time, the PRE-SAFE® function implemented in the Electronic Stability Program control unit evaluates the currently requested braking torque and initiates appropriate measures as necessary.

IMPORTANT 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 about v = 70 km/h.

Additional function requirements for autonomous braking 

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 controller unit calculates the necessary braking torque required (average deceleration approx. a = 6 m/s2) while taking the following variables into account:

The Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit sends the corresponding request to increase the braking torque and reduce the engine torque via suspension FlexRay 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.

IMPORTANT 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 

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 DISTRONIC Distance-Pilot controller unit calculates the necessary braking torque required (average deceleration approx. a = 6 m/s2) while taking the following variables into account:

The Active Brake Assist controller unit or the Distance Pilot DISTRONIC controller unit sends the corresponding request to increase the braking torque and reduce the engine torque via suspension FlexRay 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.

IMPORTANT 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   PE30.30-P-2070-97ZGA 
  Overview of system components for driver assistance systems   GF54.00-P-9998GWM
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