Active Brake Assist, Function - GF30.30-P-0020FR
Model 257, 290
up to model year 2021
with code 258 (Collision warning system with active brake application FCW-Stop)
Function requirements, general
- Active Brake Assist coded in electronic ignition lock control unit
- Active Brake Assist controller unit coded correctly
- No undervoltage or overvoltage
- Engine running or drivetrain operational:
The CDI control unit or the ME-SFI [ME] control unit transmits the "Engine running" or "Drivetrain operational" signal via drive train CAN, powertrain control unit and periphery CAN to the Active Brake Assist controller unit.
- Vehicle is not in backward movement
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 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 warning tones and brakes he/she is supported here 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 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:
- Except with code 446 (Touchpad only) it is possible to navigate with the audio/COMAND control panel. The Audio/COMAND control panel sends the respective control signals via the telematics CAN to the head unit.
- With code 446 (Touchpad only) or code 448 (Touchpad), the navigation takes place with the Touchpad. The touchpad sends the relevant operation signals to the head unit via the telematics CAN.
- The navigation can occur over voice control. The driver FSE microphone is directly read in by the head unit.
- The navigation can occur over the head unit finger navigation pad and the "Back" button on the steering wheel. The head unit finger navigation pad and the "Back" button transmit the relevant control signals via the steering wheel electronics the steering wheel CAN the steering column tube module control unit the suspension FlexRay the electronic ignition lock control unit and the user interface CAN to the head unit.
- The operating menu can be called up over vehicle button the upper control panel control unit (with code 246 (Analog clock)). The status of the Vehicle button is transmitted by the upper control panel control unit via the LCP-LIN, the Audio/COMAND control panel (except code 446 (Touchpad only)) or the touchpad (with code 446 (Touchpad only)) and the telematics CAN to the head unit.
The head unit sends the corresponding status via user interface CAN electronic ignition lock control unit and periphery CAN to the Active Brake Assist controller unit.
The following assembly parts are integrated in the Active Brake Assist controller unit:
- Radar sensor
- Control unit
The Active Brake Assist supports the PRE-SAFE® safety system.
The following presentation shows the detection range of the integral radar sensor:
Illustration of the principle of the detection range of the radar sensor, shown on model 257
The Active Brake Assist consists of the following subfunctions:
- Function sequence for distance warning
- Function sequence for braking assistance
- Function sequence for autonomous brake application
- Function sequence for emergency braking in the case of pedestrians crossing in front of the vehicle
Function sequence for 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
o
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 Electronic Stability Program control unit transmits appropriate information via the suspension FlexRay, electronic ignition lock control unit and periphery CAN to the Active Brake Assist controller unit.
Acceleration/yaw rate:
The acceleration/yaw rate is detected by the acceleration sensor integrated into the Supplemental Restraint System control unit. The Electronic Stability Program control unit transmits appropriate values via the vehicle dynamics CAN, Electronic Stability Program control unit, the suspension FlexRay, electronic ignition lock control unit and periphery CAN 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 control unit directly reads in the signals from the steering wheel angle sensor and sends them via the suspension FlexRay, electronic ignition lock control unit and periphery CAN 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 about the accelerator pedal position via the periphery CAN to the Active Brake Assist controller unit.
Brake pedal position:
The Electronic Stability Program control unit transmits information about the position of the brake pedal via the suspension FlexRay, electronic ignition lock control unit and periphery CAN to the Active Brake Assist controller unit.
Setting the turn signal (turn signaling):
The steering column tube module control unit directly reads in the switch positions of the combination switch and sends them via the suspension FlexRay, electronic ignition lock control unit and periphery CAN 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 (without code 460 (Canada version) or without code 494 (USA version)) and a collision-critical distance warning.
Static distance warning (without code 460 (Canada version) and without code 494 (USA version)):
Output of the static distance warning takes place purely optically.
If the distance from the vehicle directly ahead goes below 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 about s = 22.2 m), the Active Brake Assist controller unit sends the request to output the warning via the periphery CAN, electronic ignition lock control unit and user interface CAN to the instrument cluster.
Collision critical distance warning:
Output of the collision-critical distance warning takes place optically and acoustically.
If an obstacle within the detection range of the radar sensor is classified as accident-critical (a collision will occur within t < 2.6 s), the Active Brake Assist control unit sends the request to output the warning via the periphery CAN, electronic ignition lock control unit and user interface CAN to the instrument cluster, which then directly activates the instrument cluster speaker (intermittent alarm 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 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 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:
- with animals
- With oncoming vehicles
- With cross traffic
- in curves
Function sequence for braking assistance
If the driver then reacts to the collision-critical distance warning with emergency braking, the Brake Assist System provides support for the best possible utilization of the braking distance to the obstacle. The braking support is available in a vehicle speed range of v ≥ 7 km/h to 250 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 Electronic Stability Program control unit directly reads in the signals from the master brake cylinder pressure sensor, calculates the braking torque requested by the driver and sends this information via the suspension FlexRay, electronic ignition lock control unit and periphery CAN to the Active Brake Assist controller 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 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.
In the case of a maximum full-stop braking, the Active Brake Assist controller unit transmits the required brake force via the peripherals CAN, electronic ignition lock control unit and suspension FlexRay to the Electronic Stability Program control unit that controls the hydraulic brake pressure via the traction system hydraulic unit. For vehicles with code 299 (PRE-SAFE® system) the PRE-SAFE® function implemented in the Electronic Stability Program control unit evaluates the currently requested braking torque and, if necessary, initiates appropriate measures.
Additional function requirements for autonomous braking
- Vehicle speed: about v = 7 to 200 km/h (to the obstacles directly ahead) or about v = 7 to 50 km/h (on stationary obstacles)
- Driver seat belt fastened
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 initiates autonomous braking and a reduction in engine torque. The Active Brake Assist controller unit calculates the necessary braking torque required (average deceleration approx. a = 6 m/s2) while taking the following variables into account:
- Relative speed to vehicle or obstacle
- Distance from vehicle or obstacle
The Active Brake Assist controller unit transmits the respective request to increase the braking torque and to reduce the engine torque via periphery CAN, electronic ignition lock control unit and the 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 then reacts to the autonomous braking and brakes, the Brake Assist provides support 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: ca. v = 7 to 60 km/h
- Driver seat belt fastened
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 initiates autonomous braking and a reduction in engine torque. The Active Brake Assist controller unit calculates the necessary braking torque required (average deceleration approx. a = 6 m/s2) while taking the following variables into account:
- Relative speed to the pedestrian
- Distance to the pedestrian
The Active Brake Assist controller unit transmits the respective request to increase the braking torque and to reduce the engine torque via periphery CAN, electronic ignition lock control unit and the 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 then reacts to the autonomous braking and brakes, the Brake Assist provides support 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-P-2070-97XBA | ||
| Overview of system components for driver assistance systems | GF54.00-P-9998FR |