Active Brake Assist, function

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General

Active Brake Assist (ABA) is a driver assistance system that is intended to avoid as many critical situations as possible involving "rear-end collisions with the vehicle in front or with a stationary object", or to lessen the consequences of accidents without introducing new hazards to the road traffic.

Active Brake Assist warns (optically, acoustically), within the given system limits, if a collision is imminent.

For this purpose, the Active Brake Assist permanently assesses the traffic situation in front of the driver's own vehicle. The vehicle distances and difference in speed to the vehicles in front, to stationary obstacles in the same traffic lane or people moving around are recorded and evaluated with regard to an imminent rear-end collision. Evaluation becomes more critical the less time the driver has to react to the situation.

If this warning is ignored by the driver, a haptic braking system is then also initiated. If the driver still fails to respond, the system can reduce or avoid the severity of the accident through emergency braking. The 5th generation Active Brake Assist can trigger partial and emergency braking where moving and stationary vehicle objects are involved.

In ABA 5, sensor fusion is used between the front radar sensor and multifunction camera, which in the best case, improves the ability to react to pedestrians. A reaction to pedestrian objects occurs up to 50 km/h.

If a pedestrian walking in front of the vehicle is only recorded by the front radar sensor, the system immediately implements a haptic brake application with 50 % of the available braking power, which is also accompanied by acoustic and visual warnings.

If the front radar sensor and multifunction camera detects a walking pedestrian, then - after the haptic brake application - the system may then implement emergency braking with full braking power.

A vehicle in front or a stationary obstacle is included in the following situations in the assessment:

 The obstacle is detected for at least 1 s.

 The vehicle's own speed is greater than that of the obstacle in front (the distance decreases).

 The obstacle must have been detected at least once at a distance of > 4 m.

To do this, the front radar sensor control unit must be correctly adjusted, as otherwise the given traffic situation in front of the vehicle may be wrongly assessed.

Preconditions

 Circuit 15 ON

 The vehicle speed is greater than 10 km/h.

 The anti-lock braking system (ABS) is switched on.

 Electronic Brake Control (EBS) is functioning correctly (no faults detected)

 There are no system faults in the Active Brake Assist

Function

After the ignition is switched on, Active Brake Assist is activated and the driver assistance system control unit starts the initialization and self-test phase.

The multifunction camera and the front radar sensor control unit simultaneously detect several objects in their fields of view. Information is sent from these objects about the distance to the vehicle, the speed, offset to the driver's own vehicle and the object category (vehicle or pedestrian) to the driver assistance system control unit. The information is evaluated separately and checked for plausibility.

The Active Brake Assist is designed in such a way that in a critical situation the driver is initially warned in several warning stages. The driver is advised here of a dangerous situation through means of acoustic and visual warnings and is thereby able to respond to the given situation. If pedestrians are involved, acoustic and visual warning are issued simultaneously with a partial brake application.

The driver is hereby able to defuse the critical situation himself by braking or swerving. To do this, the Active Brake Assist evaluates all relevant driver activities which the driver can initiate to suit the situation. This ensures that the driver can keep control of his vehicle at all times.

If Active Brake Assist does not detect any appropriate driver activities, the following regulating controls are actuated:

 Visual and acoustic warning message

 A partial braking application is performed.

 If a driver reaction is not detected, emergency braking (maximum full-stop braking) is undertaken at maximum braking power until the vehicle comes to a standstill.

 If the front radar sensor control unit detects that the vehicle is not in the driving level and, consequently, the transceiver lobes of the front radar sensor control unit are not correctly aligned, Active Brake Assist is then deactivated.

Warning stages

Active Brake Assist 5 operates in 4 warning stages (warning cascade). The driver can take over control of the vehicle at any given time and can thereby intervene in the situation himself.

1 Warning

 Visual warning (red) and acoustic intermittent warning tone

 Radio and telephone muted

2 Partial braking application

 Visual warning (red) and acoustic intermittent warning tone

 Radio and telephone muted

 Partial braking application (50 %), maximum braking power = 3 m/s2

 Brake lights switched on

3 Emergency stop

 Visual warning (red) and acoustic continuous warning signal

 Radio and telephone muted

 Maximum full-stop braking (100 %), maximum braking power = approx. 6 m/s2

 Brake lights switched on

 The hazard warning lamps are activated at double frequency (4 Hz) activated at speeds  50 km/h.

4 Hold phase

 Emergency braking completed.

 Service brake remains closed for an unlimited period.

 Brake lights switched on

 Hazard warning lamps remain active at normal frequency (1.5 Hz) (if they were active in stage 3).

 Display message: "Emergency braking completed"

 Parking brake is engaged, when the driver leaves the driver's seat or opens the door.

The minimum warning period is prescribed by law and designed such that the driver can respond to a warning and take corrective measures before starting an emergency braking maneuver. The warning period is dynamic and can be adapted to the given situation.

Warning stages 1 and 2 before emergency braking lasts for at least 1.4 s. The exact duration depends on the driver's own vehicle speed, the type of obstacle involved (pedestrian or vehicle) and the dynamics of the given traffic situation.

The hold phase lasts until the driver responds.

Canceling of the warning cascade

The warning cascade can be canceled at any given time by the driver. Until the actual emergency braking maneuver is implemented, the intervention can be interrupted through a corresponding reaction, e.g. :

 Flash on and off

 Accelerate

 Kickdown

 Premature avoidance with the related loss of the object.

 An initiated emergency braking maneuver can only be aborted through a kickdown.

The following table lists the potential driver reactions to cancellation of the warning cascade in greater detail.

Switch Active Brake Assist on and off

After switching on the ignition, Active Brake Assist (ABA) is activated.

Active Brake Assist is deactivated directly through the instrument cluster or the head unit. A separate ABA switch is no longer available.

If Active Brake Assist is switched off, an indication lamp is shown on the instrument cluster.

If the system is faulty, Active Brake Assist is automatically switched off. A fault message also appears in the instrument cluster display, and the ABA indication lamp lights up permanently. Active Brake Assist cannot be switched on again where a fault condition exists.

Shown on Classic cockpit, multifunction display (A1 p1)
 Vehicles with code J6A (Classic cockpit).
Active Brake Assist is activated directly in the instrument cluster control unit (ICUC) (A1).

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Shown on Classic cockpit, instrument cluster
 Vehicles with code J6A (Classic cockpit).
ABA indication lamp in instrument cluster with switched off Active Brake Assist.

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Shown on Multimedia cockpit, screen head unit
 Vehicles with code J6B (Multimedia cockpit) or code J6C (Multimedia cockpit, interactive).
Pressing the quick entry button (1) in the head unit control unit screen takes the driver to the menu settings (2).
Active Brake Assist can be activated or deactivated using the virtual switch (arrow).

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Shown on Multimedia cockpit, screen instrument cluster
 Vehicles with code J6B (Multimedia cockpit) or code J6C (Multimedia cockpit, interactive).
ABA indication lamp in instrument cluster control unit screen with switched off Active Brake Assist.

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Reaction to pedestrian

Under ideal conditions, Active Brake Assist 5 can avoid collisions with pedestrians up to 50 km/h. This requires the walking pedestrian to be recognized here by the radar sensor and the multifunction camera in good time. If the pedestrian is only detected by the front radar sensor control unit, the system may initiate a partial braking application only.

 Walking pedestrians are detected by the front radar sensor control unit based on their oscillating movements. Camera confirmation is not required here.

The reaction to pedestrians starts immediately with a partial braking application, in order to shorten the stopping distance, as - in contrast to vehicles - pedestrians appear suddenly on the road.

After a minimum warning period of 1.4 s, emergency braking can also be initiated after a partial braking application, but only if the pedestrian has been detected by both the multifunction camera and the front radar sensor control unit.

 At vehicle speeds   > 50 km/h, there is no reaction to pedestrians.