Active Brake Assist, Function - GF30.30-S-0020TRF
Model 447
With Code BA3 (Active Brake Assist System)
With Code XM0 (Facelift)
Illustration shows MODEL 447.8
Shown On Model 447.6/7
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
- Active Brake Assist switched on in the "Assistance" menu of the instrument cluster (IC) control unit
- Engine running, powertrain operational
- Vehicle is not in backward movement
- Radar sensor system soiling and function test for the radar sensor system completed successfully
The Active Brake Assist controller unit (B92) performs a soiling and function test on the integrated radar sensor system 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.
Active Brake Assist is released manually via the operation level in the instrument cluster (IC) control unit (A1/1). The instrument cluster (IC) control unit transmits the corresponding status to the Active Brake Assist controller unit.
The CDI control unit or the ME-SFI control unit transmits the "Engine running" or "Drivetrain operational" signal to the Active Brake Assist controller unit.
Active Brake Assist, general points
Active Brake Assist with crossing function (pedestrians/cyclists) can assist the driver while braking. In order to assess the traffic situation and detect potential collisions, the assistance system evaluates information from the radar sensors. The assistance system can react to stationary or moving vehicles, as well as to crossing pedestrians and cyclists.
The assistance system is active from 7 km/h upwards, provides warnings about potential collisions visually and acoustically, and can brake the vehicle autonomously.
The system warns the driver visually at speeds from 30 km/h if the distance to the vehicle in front is too short. If the distance decreases quickly at speeds above 7 km/h so that there is a danger of a collision, it warns by means of an additional acoustic signal.
If the driver brakes, he will be assisted, if necessary, by Active Brake Assist according to the situation. It builds up additional brake pressure, if required, in order to avoid a collision as far as possible. In addition, Active Brake Assist can perform automatic braking up to maximum full-stop braking if the driver does not react sufficiently by himself. If the pressure on the brake pedal is released or the hazardous situation passes, the additional brake force is canceled.
| Function | Vehicles ahead | Stationary vehicles | Vehicles moving across in front of one's own vehicle | Crossing pedestrians/bike riders | Stationary pedestrians |
|---|---|---|---|---|---|
| Distance warning function | Up to v = Max. | Up to v = Max. | No reaction | Up to approx. v = 60 km/h | No reaction |
| Situation-based brake force boosting | Up to v = Max. | Up to approx. v = 80 km/h | No reaction | Up to approx. v = 60 km/h | No reaction |
| Autonomous braking function | Up to v = Max. | Up to v = Max. | No reaction | Up to approx. v = 60 km/h | No reaction |
The following assembly parts are integrated in the Active Brake Assist controller unit:
- Radar sensor
- Control unit
Active Brake Assist supports the PRE-SAFE® safety system (with code JP1 (PRE-SAFE)).
The following presentation shows the detection range of the integral radar sensor:
Illustration of the principle of the detection range of the radar sensor
The Active Brake Assist consists of the following subfunctions:
- Distance warning function
- Situation-based brake force boosting
- Autonomous braking function
- Emergency braking in case of crossing pedestrians/cyclists
Distance warning function
Apart from data from the radar sensor, the Active Brake Assist controller unit also 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 on the basis of the wheel speeds. The Electronic Stability Program (ESP) control unit transmits corresponding information to the Active Brake Assist controller unit.
- Acceleration/yaw rate:
- The acceleration/yaw rate is detected by the sensor turn rate, transverse and longitudinal acceleration integrated in the Electronic Stability Program (ESP) control unit. The Electronic Stability Program (ESP) control unit transmits corresponding values to the Active Brake Assist controller unit.
- Steering wheel angle:
- The steering angle sensor records the steering wheel angle. The steering column tube module (MRM) control unit reads in the signals of the steering angle sensor directly and transmits information on the steering wheel angle to the Active Brake Assist controller unit. The data from the steering angle sensor serve to test the plausibility of the turn rate detected by the yaw rate sensor for lateral and longitudinal acceleration.
- Driver activity:
The driver activity is described based on different factors, which is described in the following.
- Accelerator pedal position:
The powertrain control unit transmits information about the accelerator pedal position to the Active Brake Assist controller unit.
- Brake pedal position:
The Electronic Stability Program (ESP) control unit transmits information on the position of the brake pedal to the Active Brake Assist controller unit.
- Setting the turn signal lights (turn signaling):
The steering column tube module (MRM) control unit reads in the switch position of the combination switch directly and transmits it to the Active Brake Assist controller unit.
- Accelerator pedal position:
The Active Brake Assist controller unit calculates the distance to the obstacle and the time up to a possible collision. In the process, the Active Brake Assist controller unit differentiates between the following warnings:
- Static distance warning:
- Output of the static distance warning takes place purely optically.
If the distance to the vehicle in front falls below t = 0.8 s in flowing traffic and this critical distance is maintained for t > 3 s (e.g. at a speed of v = 100 km/h, distance of approx. s = 22.2 m), the Active Brake Assist controller unit transmits the request to output the warning to the instrument cluster (IC). The IC control unit (IC) reacts by actuating the DISTRONIC warning lamp.
- Output of the static distance warning takes place purely optically.
- 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 (a collision will occur within t < 2.6 s), the Active Brake Assist controller unit transmits the warning output request to the instrument cluster (IC) control unit that then activates the DISTRONIC warning lamp and directly actuates the IC speaker (intermittent warning tone).
- Output of the collision-critical distance warning takes place optically and acoustically.
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 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 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.
Warning indicator in instrument cluster
Situation-based 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. Brake force boosting is available in a vehicle speed range from 7 km/h to the maximum design speed.
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 the master brake cylinder brake pressure sensor (N30/4b1). The Electronic Stability Program (ESP) control unit directly reads in the signals of the master brake cylinder brake pressure sensor, calculates the braking torque requested by the driver and transmits this information to the Active Brake Assist controller unit.
In the event of maximum full-stop braking, the Active Brake Assist controller unit transmits the necessary brake force to the Electronic Stability Program (ESP) control unit, which controls the hydraulic brake pressure via the traction system hydraulic unit (2).
For vehicles with code JP1 (PRE-SAFE), the PRE-SAFE® function implemented in the Electronic Stability Program (ESP) 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 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.
The Active Brake Assist can react to stationary vehicles up to a ground speed of approx. 80 km/h.
Additional function requirements for autonomous braking function
- Vehicle speed: from approx. 7 km/h to maximum speed (to vehicles in front or stationary vehicles) or from approx. 7 to 60 km/h (to crossing pedestrians/cyclists)
- Driver seat belt fastened
Autonomous braking function
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 necessary
braking torque (maximum deceleration of approx. a = 6 m/s2 ) while taking the following variables into account:
- 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 the engine torque to the Electronic Stability Program (ESP) control unit. The Electronic Stability Program (ESP) control unit evaluates the incoming requests, actuates the traction system hydraulic unit directly, and transmits the request to reduce engine torque to the CDI control unit or the ME-SFI [ME] control unit.
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 crossing pedestrians/cyclists
- Vehicle speed: Approx. 7 to 60 km/h
- Driver seat belt fastened
Emergency braking in case of crossing pedestrians/cyclists
If the radar sensor system detects crossing pedestrians, the Active Brake Assist controller unit issues a static or collision-critical distance warning.
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 necessary braking torque while taking the following variables into account:
- Speed differential to the pedestrian.
- Distance to the pedestrian.
The Active Brake Assist controller unit transmits the corresponding request to increase the braking torque and to reduce the engine torque to the Electronic Stability Program (ESP) control unit. The Electronic Stability Program (ESP) control unit evaluates the incoming requests, actuates the traction system hydraulic unit directly, and transmits the request to reduce engine torque to the CDI control unit or the ME-SFI [ME] control unit.
| Overview of system components for driver assistance systems | GF54.00-S-9998TRF |