Active Brake Assist, function

S30.30-A000-79

S30.30-A013-79

Function requirements for Active Brake Assist

 no undervoltage or overvoltage.

 Engine running.

 Vehicle not moving backwards.

 Active Brake Assist switched on in the "Assistance" menu of the instrument cluster (IC) control unit.

 Collision warning system radar sensor soiling and function test completed successfully.

 The collision warning system radar sensor performs a soiling and function test after every engine start. The function test requires an object to be located in the detection area (this object is used as a reference value). If malfunctions are detected or if no function test is possible, the Active Brake Assist cannot be activated.

 The Active Brake Assist is released manually via the operation level in the instrument cluster (IC) control unit. The instrument cluster control unit (IC) transmits the corresponding status to the collision warning system radar sensor.

Active Brake Assist, general points

The Active Brake Assist continuously checks the following distance to the vehicle or pedestrian immediately ahead and warns the driver acoustically against possible collisions. In an imminent collision situation, the Active Brake Assist initiates autonomous partial braking.

To do this, the collision warning system radar sensor and the multifunction camera control unit evaluate the traffic situation in front of the vehicle, the route immediately in front as well as the driver activity and constantly determine the risk potential of a possible collision.

The multifunction camera control unit detects pedestrians who are in the danger zone in front of the vehicle in a vehicle speed range of 10 to 60 km/h.

The multifunction camera control unit does not detect any pedestrians under the following conditions:

 in darkness or in a tunnel

 in the event of heavy light incidence such as sun or headlights of oncoming vehicles

 If the profile cannot be detected as a pedestrian.

The collision warning system radar sensor detects vehicles and other objects located in the hazard area in front of the vehicle in a speed range over 5 km/h.

The collision warning system radar sensor does not detect any of the following objects:

 sitting or small pedestrians (children)

 animals

 Bike riders, skates, skateboards etc.

 wheelchair users or other invalid chairs

If the driver reacts to the warning tone and brakes, he is supported. 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 consists of the following subfunctions:

 Function sequence for distance warning

 Function sequence for autonomous partial braking

Function sequence for distance warning

In addition to the radar data, the collision warning system radar sensor evaluates the following variables:

 Direction of travel and vehicle speed

 Acceleration/yaw rate

 Steering wheel angle

 Driver activity:

Direction of travel and vehicle speed

The direction of travel is defined using the wheel rotation direction. The vehicle speed is calculated on the basis of the wheel speeds. The Electronic Stability Program control unit (ESP) transmits the corresponding information to the collision warning system radar sensor.

Acceleration and yaw rate

The acceleration and yaw rate are registered by the yaw rate sensor for lateral and longitudinal acceleration integrated in the Electronic Stability Program (ESP) control unit. The Electronic Stability Program control unit (ESP) transmits the corresponding information to the collision warning system radar sensor.

Steering wheel angle

The steering wheel angle is registered by the steering wheel angle sensor integrated in the steering column tube module control unit (MRM). The steering column tube module control unit (MRM) transmits the corresponding information to the collision warning system radar sensor. The data from the steering wheel angle sensor serve to test the plausibility of the turn rate detected by the yaw rate sensor for lateral and longitudinal acceleration.

Driver activity:

 Accelerator pedal position - registered by the accelerator pedal module.

 Brake pedal position - registered by the brake light switch.

 Setting of the turn signal lights (turn signaling) - registered by the combination switch.

Accelerator pedal position

The CDI control unit or ME-SFI [ME] control unit transmits information on the accelerator pedal position to the collision warning system radar sensor.

Brake pedal position

The Electronic Stability Program control unit (ESP) transmits information on the position of the brake pedal to the collision warning system radar sensor.

Setting the turn signal lights (turn signaling):

The steering column tube module control unit (MRM) reads in the switch position of the combination switch directly, and transmits it to the collision warning system radar sensor.

The collision warning system radar sensor calculates the distance to the obstacle and the time to a possible collision. The radar sensor collision warning system differentiates here between the following warnings:

 Static distance warning

 Collision critical distance warning:

Static distance warning

Output of the static distance warning takes place purely optically.

Collision critical distance warning:

The collision-critical distance warning is output optically by the DISTRONIC warning lamp and acoustically.

If an obstacle in the detection range of the radar sensor is classified as accident-critical, the collision warning system radar sensor transmits the request to output the warning.

The warning output cannot be acknowledged. Take-back of the warning only occurs if the situation has been defused.

To output the warning, the collision warning system radar sensor gives consideration to the driver's activity and the likely route in addition to the vehicle speed and the distance to an obstacle.

The driver activity is detected, for example, through modifications of the accelerator pedal position, through actuation of the turn signal lights or through pressing the brake pedal. The route ahead is defined over the yaw rate, the steering wheel angle and the direction of travel.

S54.33-0006-71

Function sequence for autonomous partial braking

If the driver fails to react in an accident-critical situation to the warning, the collision warning system radar sensor initiates autonomous partial braking and reduction in engine torque. The collision warning system radar sensor calculates the necessary braking torque (maximum deceleration approx. 6 m/s2). The output of the warning tone and the optical warning is continued.

The collision warning system radar sensor transmits the corresponding request to increase the braking torque and to reduce the engine torque to the Electronic Stability Program control unit (ESP). The Electronic Stability Program control unit (ESP) actuates the traction system hydraulic unit directly. It also transmits the request to reduce the engine torque to the CDI control unit or the ME-SFI [ME] control unit.