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Adaptive Brake Function - GF42.47-P-0002RR

Model 190 

G16681699Courtesy of MERCEDES-BENZ USA

Block diagram 

Function requirements, general 

ADAPTIVE BRAKE, general 

ADAPTIVE BRAKE assists the driver in dangerous situations which occur suddenly, and thus enhances active safety.

To do so, the Electronic Stability Program control unit evaluates the data from the following components in order to detect the current driving situation:

The system is made up of the following subfunctions:

Function sequence for ESP® 

ESP® prevents the vehicle from breaking away when oversteering or understeering. It ensures that the vehicle does not deviate from the course specified by the driver (within physical limits).

Brake forces are produced selectively at the individual wheels to correct any deviations.

Furthermore, reduction of the drive torque takes place in order to increase driving stability.

The Electronic Stability Program control unit processes the following measured quantities to determine the vehicle behavior:

Differentiation is made between the following intervention types:

Intervention in the case of oversteer 

If the vehicle begins to oversteer, brake pressure is built up at the outer front wheel. The resulting reduction in lateral force at the outer front wheel generates a yawing moment which counteracts the tendency of the vehicle to rotate inward. The vehicle speed decreases as a result of the brake force at the front wheel, which also enhances stability.

Intervention in the case of understeer 

If the vehicle understeers, the maximum possible lateral force at the front axle has been exceeded. In other words, the vehicle pushes via the front axle to the outer edge of the curve.

The resulting instability is counteracted by means of a reduction in drive torque and the following brake interventions at up to 3 wheels:

Depending on the brake force, a torque is generated which causes the vehicle to rotate inward with a simultaneous reduction in speed. This has a considerable stabilizing effect. The Electronic Stability Program control unit sends via chassis CAN 1 and the engine CAN with the powertrain control unit interface a signal requesting reduction of the drive torque to the ME-SFI control unit which reduces the engine power accordingly.

A pending shift operation is suppressed for the duration of control intervention.

For this purpose, the Electronic Stability Program control unit sends a signal via chassis CAN 1, the powertrain control unit and drive train CAN to the dual clutch transmission control unit. The latter control unit suppresses the shift operation.

EBD function sequence 

The EBD [EBV] function provides assistance when the driver applies medium force to the brake pedal.

EBD [EBV] prevents overbraking of the rear axle and increases vehicle stability when braking in a curve by reducing the pressure at the rear wheel on the inside of the curve or increasing it at the front wheel on the outside of the curve as required. The side-slip angle (angle between vehicle longitudinal axis and direction of movement of the vehicle's center of gravity) is calculated using the yaw rate (speed of vehicle rotation about vertical axis).

The yaw rate, the lateral acceleration and the turning angle of the front wheels (calculated from the steering wheel angle) can be used to determine the lateral forces on the wheels. The longitudinal forces on the wheels are calculated using the engine torque, transmission shift stage and brake pressure at each wheel.

If the measured yaw rate does not match the specified value or if the determined side-slip angle is too large, the Electronic Stability Program control unit generates a signal for brake force buildup or reduction for the relevant wheel. The resulting forces stabilize the vehicle.

Function sequence of exhaust test, dynamometer test mode 

For vehicle test purposes, the ADAPTIVE BRAKE can be set to dynamometer test mode if the workshop menu is activated via the instrument cluster and the engine is then started. ESP®, ABS and ASR are then switched to passive. The Electronic Stability Program warning lamp and the antilock brake system indicator lamp in the instrument cluster light up. Additionally, a corresponding message is shown in the instrument cluster. The roller dynamometer mode can also be activated via XENTRY Diagnostics.

Function sequence for Torque Vectoring Brake 

Torque Vectoring Brake is the active influence of the yaw angle or the yaw acceleration on the rear axle through interventions by the brake system. When cornering, a short intervention by the brake system on the rear wheel on the inside of the curve causes the vehicle to rotate to a certain extent. The vehicle can be steered more precisely and easily and there is a noticeable improvement in the responsiveness and driving safety. Torque Vectoring Brake enables stable cornering without any noticeable loss in accelerating power while driving in the sporty driving mode.

ABS function sequence 

ABS prevents the wheels locking when braking and as a result maintains the steerability and directional stability and road adhesion during the vehicle deceleration. If a locking wheel is detected by the Electronic Stability Program control unit on the basis of the signals from the RPM sensors, the brake pressure is reduced at the appropriate wheel until the wheel begins to turn again.

Function sequence for ASR, ETS 

ASR and ETS prevent the drive wheels from spinning when driving. ASR and ETS also serve to provide improved directional stability and road adhesion for increased traction potential over the entire vehicle speed range. Spinning of the drive wheels is detected by the Electronic Stability Program control unit using the signals from the RPM sensors. Wheel spinning is countered by reduction of the drive torque.

For this purpose, the Electronic Stability Program control unit sends via chassis CAN 1 and the engine CAN with the powertrain control unit interface a signal requesting reduction of the drive torque to the ME-SFI control unit which reduces the engine power accordingly. A check is continuously performed to establish whether the drive torque specified by the driver via the accelerator pedal sensor can be permitted again, e.g. due to an improvement in road surface adhesion. The drive torque is transmitted to the opposite, stable drive wheel by means of intervention by the brake system on the spinning wheel.

Function sequence for AMG TRACTION CONTROL (for model 190.379) 

The AMG TRACTION CONTROL is a 9-stage traction control, that enables the driver to pre-select the slip on the driven rear axle in nine stages. The maximum permissible rear wheel drive slip is calculated to match the mode involved. When the rear wheels reach the specified slip level, engine power is regulated by the traction control so that the level is not exceeded and the vehicle continues to accelerate with the specified slip.

The driver can select the required stage using the autonomous traction control switch in the center console. A corresponding message is shown on the instrument cluster. The autonomous traction control switch signal is read in by the AMG gateway control unit over the AMG DRIVE UNIT-LIN. The AMG gateway control unit sends the signal over the chassis CAN 1 to the Electronic Stability Program control unit.

Spinning of the drive wheels is detected by the Electronic Stability Program control unit using the signals from the RPM sensors. Wheel spinning is countered by reduction of the drive torque.

For this purpose, the Electronic Stability Program control unit sends via chassis CAN 1 and the engine CAN with the powertrain control unit interface a signal requesting reduction of the drive torque to the ME-SFI control unit which reduces the engine power accordingly. A check is continuously performed to establish whether the drive torque specified by the driver via the accelerator pedal sensor can be permitted again, e.g. due to an improvement in road surface adhesion. The drive torque is transmitted to the opposite, stable drive wheel by means of intervention by the brake system on the spinning wheel.

BAS function sequence 

The BAS detects emergency braking situations based on rapid actuation of the brake pedal and, if necessary, increases the brake pressure in order to achieve maximum deceleration. For this purpose, the Electronic Stability Program control unit evaluates the increase in pressure in the brake system and initiates an emergency stop if a certain triggering threshold is exceeded.

Function sequence for BAS PLUS (with CODE P20 (Driving assistance package)) 

BAS Plus increases the brake pressure depending on the speed of the brake pedal operation and the distance to the vehicle driving in front.

Function sequence - Fail boost 

The fail boost function ensures brake boosting. It is activated if the pneumatic brake booster cannot adequately support driver braking because of a system error in the vacuum supply.

The failure of the pneumatic brake booster is detected via the brake vacuum sensor, which is integrated in the pneumatic brake booster.

The fail boost function performs hydraulic brake boosting using a suitable boost factor and actuates the valves and the traction system hydraulic unit for this accordingly.

Hill Start Assist function sequence 

When starting off, the Hill-Start Assist prevents the vehicle from rolling back opposite the travel direction of the engaged gear range during the time it takes for the driver to change from the brake pedal to the accelerator pedal.

The function is released automatically if, when the vehicle is stationary, an uphill or downhill gradient which would cause the vehicle to roll opposite the travel direction of the engaged gear range is detected by the Electronic Stability Program control unit. The Electronic Stability Program control unit reads in the signal from the brake light switch directly and in this way detects the status of the brake pedal.

The electric parking brake control unit transmits the status of the electric parking brake via chassis CAN 1 to the Electronic Stability Program control unit.

The brake pressure applied by the driver is maintained in the brake system by the traction system hydraulic unit.

Following release of the brake pedal and detection of a start-off request, reduction of the brake pressure is controlled by means of torque balancing system. This system takes into consideration the incline output torque, the total braking torque and the available drive torque.

When the start-off torque is high enough, the Hill-Start Assist is deactivated and the vehicle starts off without rolling in the undesired direction of travel.

If the driver does not depress the brake pedal, the pressure in the brake system is reduced after t = 1 s.

The Hill-Start Assist is terminated immediately if:

The Hill-Start Assist does not function if:

Additional function requirements for adaptive brake lights flashing (except with code 494 (USA version)) 

Function sequence for adaptive brake lights flashing (except with code 494 (USA version)) 

In the event of emergency braking, the Electronic Stability Program control unit sends a corresponding signal to the rear SAM control unit with fuse and relay module via chassis CAN 1 and the interior CAN with the front SAM control unit with fuse and relay module interface.

The rear SAM control unit with fuse and relay module actuates for the duration of the signal (min. 1 s) the rear left lamp unit, rear right lamp unit and the center brake lamp at a flasher frequency of 5 Hz. If the vehicle comes to a standstill from a speed > 70 km/h (not urban traffic), the brake lights and the additional brake lamp are permanently actuated again. In addition, the automatic hazard warning flasher function is activated. If the vehicle then exceeds a speed of 10 km/h, the hazard warning system is automatically switched off again.

Additional function requirements - dry braking 

IMPORTANT The status of the windshield wiper system is sent by the front SAM control unit with fuse and relay module via chassis CAN 1 to the Electronic Stability Program control unit.

Dry braking function sequence 

The dry braking function enhances the performance of the brakes on the front axle in wet driving conditions. Cyclical application of the brake pads for a brief period (approx. 0.5 s) at a brake pressure of p = 1 bar, ejects the water film from the brake disks. This improves the response time of the brake.

Function sequence for precharging dependent on accelerator pedal operation 

Upon detection of a possible emergency braking situation, the brake pads are brought into contact with the brake disks. The clearance between the brake lining and brake disk is thus compensated before the driver operates the brake. The response time of the brake is improved and a shorter braking distance is achieved.

Emergency braking is detected on the basis of the release gradient of the accelerator pedal. If a rapid release of the accelerator pedal is detected, the system assumes that the driver intends to brake. The function is activated and a brake pressure of p = 2 to 3 bar is requested.

IMPORTANT In order to adapt the calculated triggering threshold of the release gradient to the driver behavior, a learning algorithm is implemented which places the driver in the category "normal driver" or "hectic driver" on the basis of the average rate at which the accelerator pedal is released.

Function sequence for precharging depending on lateral acceleration 

During dynamic cornering, the brake linings are brought into contact with the front axle brake disks. This closes the air gap between the brake pad and brake disk in order to achieve the required braking power at the corresponding wheel as quickly as possible in the event of ESP® intervention by the brake system.

Function sequence for HOLD function 

The HOLD function assists the driver during waiting times in traffic or when starting off on a hill. The HOLD function is activated by briefly and quickly depressing the brake pedal when the vehicle is stationary.

Successful activation of the HOLD function is indicated in a status line in the instrument cluster.

The HOLD function can be activated if:

If the driver releases the brake pedal, an incline-dependent hold pressure is set and maintained until the driver quickly depresses the brake pedal again or drives off. Pressure reduction when starting off is performed by the standstill control depending on the respective situation.

The HOLD function is deactivated automatically if:

Function sequence for switching ESP® to passive mode 

ESP® can be operated in 3 different operating modes. You can switch between the operating conditions by pressing the ESP Sport Off AMG button. To switch between ESP® ON and ESP® Sport, press the AMG ESP Sport Off button only briefly. To switch off the ESP®, press and hold the AMG ESP Sport Off button for t > 2.5 s. The status of the AMG ESP Sport Off button is read in by the AMG gateway control unit and sent via chassis CAN 1 to the Electronic Stability Program control unit.

The operating modes are:

ESP® ON 

ABS, ASR and ESP® operate with adapted control thresholds. The Electronic Stability Program warning lamp and the ESP®/ASR OFF warning lamp in the instrument cluster are off, and the Electronic Stability Program warning lamp flashes on and off during ESP® control.

ESP® Sport 

ABS operates with adapted control thresholds. When engine torque control is active, ASR operates with significantly reduced intervention strength and adjusted single-sided brake system interventions to improve traction.

ESP® operates with reduced intervention intensity and adapted control thresholds. The Electronic Stability Program warning lamp in the instrument cluster is always on and flashes during ESP® control. The message "ESP SPORT" appears in the instrument cluster.

ESP® OFF 

The ABS is configured for maximum deceleration. Ride comfort is of secondary importance. The ASR operates without engine torque control. Only the single-sided brake system interventions to improve traction are active. ESP® is completely deactivated, no engine torque or brake interventions whatsoever are made.

The Electronic Stability Program warning lamp and the ESP®/ASR OFF warning lamp in the instrument cluster remain permanently lit. The message "ESP OFF" appears in the instrument cluster.

IMPORTANT All PRE-SAFE® functions are deactivated in ESP® OFF mode.

Function sequence for PRE-SAFE® system 

The PRE-SAFE® system is activated in critical driving conditions, i.e. in a potential accident situation. The objective is to create the most favorable conditions possible for the vehicle occupants during an expected accident, by activating the functions before the actual impact.

The PRE-SAFE® system is integrated in the Electronic Stability Program control unit. If the Electronic Stability Program control unit detects one of the following situations, the PRE-SAFE® system is activated:

IMPORTANT If emergency braking or panic after-braking is detected in the Electronic Stability Program control unit, there is no automatic engine stop by the ECO start/stop function.

Function sequence for standstill control (SSC) 

The standstill control monitors the HOLD function below a speed of 3 km/h until the vehicle comes to a safe standstill. Within this vehicle speed range, the SSK is responsible of the transfer to a safe state when a securing event occurs.

When the vehicle is at a safe standstill, the rolling monitoring function of the SSC is requested by the driver assistance system. If vehicle rolling is detected, the brake pressure is increased until the vehicle is stationary again.

Securing the vehicle by means of the SSC is necessary if the following events occur:

IMPORTANT The status of the driver seat belt buckle is detected by the driver belt buckle restraint system switch and read in by the supplemental restraint system control unit. The supplemental restraint system control unit sends the status via chassis CAN 1 to the Electronic Stability Program control unit.

Door contact plausibility check 

The plausibility check detects any faults along the signal path from the left door lock rotary tumbler switch or the right door lock rotary tumbler switch (depending on the global country coding for left-hand or right-hand drive vehicle), read in by the left door control unit or right door control unit and via the interior CAN and chassis CAN 1, with the front SAM control unit with fuse and relay module interface to the Electronic Stability Program control unit. If, as the result of an electrical or mechanical fault, "Driver door closed" is detected by mistake although the driver door is open, this is detected by the door contact plausibility check in the SSC and a corresponding fault is stored in the Electronic Stability Program control unit.

SSC deactivation 

Deactivation of the SSK is signaled internally in the Electronic Stability Program control unit and externally over the chassis CAN 1. Activation of the driver assistance system is no longer possible. Securing of the vehicle is additionally requested immediately if the SSK is deactivated and a driver assistance system is active.

Securing vehicle 

The vehicle is secured by the comfort securing system of the electric parking brake, which is prompted to lock by the SSC. For this purpose, the Electronic Stability Program control unit sends a signal via the chassis CAN 1 to the electric parking brake control unit. The vehicle is secured after the locking request has been implemented and the feedback signal to confirm that the electric parking brake is applied has been sent from the electric parking brake control unit to the Electronic Stability Program control unit. The existing brake pressure at the wheels is reduced and the SSK becomes inactive.

If the close request is not implemented by the electric parking brake within a defined time or the electric parking brake signals a system fault to the SSC, the electric parking brake is detected as being defective and the safety strategy becomes active.

Safety strategy, request engage "P" or Emergency-P path 

The safety strategy is implemented via the DIRECT SELECT INTERFACE. The Electronic Stability Program control unit sends a request to engage gear range "P" to the DIRECT SELECT INTERFACE via chassis CAN 1, the powertrain control unit and drive train CAN. The vehicle is secured after gear range "P" is engaged by the DIRECT SELECT INTERFACE and following feedback to the Electronic Stability Program control unit. The existing brake pressure at the wheels is reduced and the SSC becomes inactive.

If the DIRECT SELECT INTERFACE does not signal engagement of gear range "P" within a defined time, the Emergency-P function of the electronic ignition lock control unit forces gear range P to be engaged.

For this purpose, the electronic ignition lock control unit also receives the request for engaging gear range "P" from the Electronic Stability Program control unit via chassis CAN 1 and itself sends a request to the DIRECT SELECT INTERFACE. If the electronic ignition lock control unit does not receive any feedback from the DIRECT SELECT INTERFACE within a defined time, the Emergency-P path is energized by the electronic ignition lock control unit following enabling by the DIRECT SELECT INTERFACE, and engagement of gear range "P" in the DIRECT SELECT INTERFACE is forced by a spring mechanism.

System fault display 

The driver is informed about the system status and about faults by the following displays:

If the Electronic Stability Program control unit fails, basic braking without ABS is always available.

IMPORTANT The status of the brake fluid level switch is read in by the front SAM control unit with fuse and relay module and sent to the instrument cluster via the interior CAN and user interface CAN with the AMG gateway control unit interface.

  Electrical function schematic for ADAPTIVE BRAKE   PE42.47-P-2051-97HBA
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