Active Brake Assist, Function - GF30.30-D-0020TSA

Model 907

with code BA3 (Active Brake Assist System)

Shown on model 907

Function requirements, general

Active Brake Assist coded in the electronic ignition lock control unit (EZS).
Active Brake Assist controller unit coded correctly.
no undervoltage or overvoltage.
Engine running, powertrain operational:
The CDI control unit or the ME-SFI control unit transmits the "engine running" or "powertrain operational" signal via the drive CAN, powertrain control unit, and suspension FlexRay to the Active Brake Assist controller unit.
Vehicle not moving backwards.

Active Brake Assist, general points

The Active Brake Assist continuously checks the safe distance to the vehicle in front. It visually and acoustically warns the driver of possible collisions (e. g. rear-end collision) with other vehicles and helps, in this connection, to significantly reduce the risk of an accident. In a collision-critical situation, the Active Brake Assist initiates an autonomous brake application if applicable.

To do this the Active Brake Assist controller 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 the vehicle speed range between 7 and 250 km/h. If the driver reacts to the warnings and brakes, he/she is supported by the Active 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. A possible collision can thus be prevented or its consequences at least reduced.

The Active Brake Assist detects crossing pedestrians, who are located in the danger zone in front of the vehicle, in a vehicle speed range between 7 and 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. For pedestrians who step relatively late into the hazard area, the Assist brakes at the same time as the warning in order to reduce the speed even faster.

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 navigation takes place via the head unit control panel control unit, which transmits the operation signals via the telematics CAN to the head unit.
The navigation in the operating menu can also be realized with the head unit finger navigation pad and the "Back" button on the steering wheel. The steering wheel electronics reads in the operation signals of the head unit finger navigation pad (S163/2s10) and "Back" button (S163/2s13). It transmits these via the steering wheel CAN, steering column tube module control unit (MRM), suspension FlexRay, electronic ignition lock control unit (EZS) and user interface CAN to the head unit.

The head unit transmits the status of the Active Brake Assist via the user interface CAN, electronic ignition lock control unit (EZS) and suspension FlexRay to the Active Brake Assist controller unit.

The following assembly parts are integrated in the Active Brake Assist controller unit:

Radar sensor
Control unit

Illustration of the principle of the detection range of the radar sensor

The Active Brake Assist consists of the following subfunctions:

Distance warning
Brake force boosting
Autonomous brake application
Emergency braking in case of crossing pedestrians

Distance warning

Apart from data from the radar sensor, the Active Brake Assist controller unit also 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 ESP® control unit transmits the corresponding information via suspension FlexRay to the Active Brake Assist controller unit.

Reverse gear is detected as follows:

In model 907 by the fully integrated transmission control (VGS) electric controller unit

The respective signal is transmitted via the drive CAN, powertrain control unit, and suspension FlexRay to the Active Brake Assist controller unit.

Acceleration/yaw rate:

The yaw torque interface is integrated in the ESP® control unit. The ESP® control unit transmits it via suspension FlexRay to the Active Brake Assist controller unit.

Steering wheel angle:

The steering wheel angle sensor detects/records the steering wheel angle. The steering column tube module (MRM) control unit reads in the signals of the steering wheel angle sensor directly and transmits information on the steering wheel angle via suspension FlexRay to the Active Brake Assist 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 transmits information on the accelerator pedal position via suspension FlexRay to the Active Brake Assist controller unit.

Brake pedal position:

Information on the position of the brake pedal is detected by the master brake cylinder pressure sensor. The ESP® control unit detects the signals, evaluates them, and transmits them via suspension FlexRay to the Active Brake Assist controller unit.

Setting the turn signal (turn signaling):

The steering column tube module (MRM) control unit reads in the switch position of the combination switch directly and transmits it via suspension FlexRay to the Active Brake Assist controller unit.

The Active Brake Assist controller unit calculates the distance to the obstacle and the time up to a possible collision. The Active Brake Assist controller unit differentiates here between a static and collision-critical distance warning.

Static distance warning:

Output of the static distance warning takes place purely optically.

If the distance to the vehicle in front undershoots 0.8 s in moving traffic and remains in this critical distance for longer than 3 s (e. g. at a speed of 100 km/h, distance approx. 22.2 m), the Active Brake Assist controller unit transmits the warning output request via the suspension FlexRay, electronic ignition lock control unit (EZS) and user interface CAN to the instrument cluster. The instrument cluster reacts by actuating the DISTRONIC warning lamp.

Collision critical distance warning:

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

If an obstacle is classified as accident-critical in the radar sensor detection range (collision within less than 2.6 s), the Active Brake Assist controller unit transmits the warning output request via the suspension FlexRay, electronic ignition lock control unit (EZS) and user interface CAN to the instrument cluster. This then activates the DISTRONIC warning lamp and directly actuates the warning buzzer (intermittent warning tone).

The warning output cannot be acknowledged. The warning is only canceled once the situation has defused.

For output of the warning the Active Brake Assist controller unit also takes the driver activity and the route directly ahead into account along with the vehicle speed and the distance to an obstacle, as well as the driver activity and the road ahead. 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 to obstacles driving in front up to a ground speed of 250 km/h and to stationary obstacles up to approx. 200 km/h, e. g. stopped or parking vehicles.

The collision-critical distance warning is not output in the following cases:

In the case of animals
For oncoming vehicles
For cross traffic
in curves

Brake force boosting

If the driver reacts to the collision-critical distance warning with maximum full-stop braking, he/she is supported by the Active Brake Assist for the best possible utilization of the braking distance to the obstacle. The brake force boosting is available in a vehicle speed range of 7 to 250 km/h for obstacles driving in front or up to approx. 200 km/h in the case of stationary obstacles.

The Active Brake Assist can react to stationary vehicles up to a ground speed of approx. 80 km/h.

The Active Brake Assist controller 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 master brake cylinder brake pressure sensor. The ESP control unit® directly reads in the signals of the master brake cylinder pressure sensor, calculates the braking torque requested by the driver and transmits this information via the suspension FlexRay to the Active Brake Assist controller unit.

In the case of a maximum full-stop braking, the Active Brake Assist controller unit transmits the corresponding request via the suspension FlexRay to the ESP® control unit. This controls the brake pressure via the traction system hydraulic unit.

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 the actuation of the brake pedal by the driver decreases considerably, the brake force boosting on the driver braking is reduced and the Active Brake Assist is deactivated. If the driver actuates the accelerator pedal, the Active Brake Assist is also deactivated.

Additional function requirements for autonomous braking

Vehicle speed: Approx. 7 to 250 km/h (to obstacles driving in front) or approx. 7 to 200 km/h (to stationary obstacles)
Driver seat belt fastened

Autonomous brake application

If the driver fails to react in an accident-critical situation to the warning, the Active Brake Assist controller unit initiates autonomous braking and a reduction in engine torque. The Active Brake Assist controller unit calculates the required braking torque (average deceleration approx. 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 transmits the corresponding request to increase the braking torque and to reduce engine torque via suspension FlexRay to the ESP® control unit. The ESP® control unit evaluates the incoming requests and directly actuates the traction system hydraulic unit. It also transmits the engine torque reduction request via the suspension FlexRay, powertrain control unit and drive CAN to the CDI control unit or the ME-SFI [ME] control unit.

If the driver reacts to the autonomous brake application and brakes, he/she is supported by the Active Brake Assist for the best possible utilization 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. 7 to 60 km/h
Driver seat belt fastened

Emergency braking in case of crossing pedestrians

Speed differential to the pedestrian.
Distance to the pedestrian.

If the driver reacts to the autonomous brake application and brakes, he/she is supported by the Active Brake Assist for the best possible utilization 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	PE30.30-D-2070-97TSA
Overview of system components for driver assistance systems	GF54.00-D-9998TSA