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Home >> Mercedes Benz >> 2015 >> C300 Base >> Repair and Diagnosis >> Brakes >> Mechanical - Hydraulic >> Brakes - Hydraulic & Mechanical System - 205 Chassis (4D Sedan) >> Basic Knowledge >> Adaptive brake (ABR), function - GF42.47-P-0001RF

Adaptive brake (ABR), function - GF42.47-P-0001RF

Model 205 (except 205.012/047/147/212/247), 253 (except 253.354/954) 

Fig 1: Adaptive Brake Block Diagram (Except AMG Vehicles With Engine 177)
G10133439Courtesy of MERCEDES-BENZ USA

Block diagram (except AMG vehicles with engine 177) 

Fig 2: Adaptive Brake Block Diagram (AMG Vehicles With Engine 177)
G10133440Courtesy of MERCEDES-BENZ USA

Block diagram (for AMG vehicles with engine 177) 

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:

ADAPTIVE BRAKE is available in 2 variants:

IMPORTANT There are no differences between the variants with respect to the ADAPTIVE BRAKE subfunctions described below.

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 a signal to reduce the drive torque via the chassis FlexRay, electronic ignition lock control unit, periphery CAN, powertrain control unit and engine CAN to the CDI control unit (with diesel engine) or the ME-SFI [ME] control unit (with gasoline engine), 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 to the fully integrated transmission control unit via chassis FlexRay, electronic ignition lock control unit, periphery CAN, powertrain control unit and drive train CAN. 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 

The ABS prevents the wheels from blocking when braking and as a result maintains the steerability and driving stability during 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, the Electronic Stability Program control unit sends a signal to reduce the drive torque via the chassis FlexRay, electronic ignition lock control unit, periphery CAN, powertrain control unit and engine CAN to the CDI control unit (with diesel engine) or the ME-SFI [ME] control unit (with gasoline engine), 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 Brake Assist System PLUS (with code 23P (Driving Assistance package Plus)) 

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

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 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. It 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

Function sequence for Downhill Speed Regulation (DSR) (on model 253 with CODE 430 (Off-road package)) 

DSR provides additional reliability in steep terrain. The speed setting for the DSR function can be set in a range of v = 4 km/h to v = 18 km/h in 1 km/h steps via the corresponding menu in the instrument cluster. The system is activated using the Downhill Speed Regulation button in the off-road operating panel.

Activation is indicated by an LED in the Downhill Speed Regulation button.

The request to activate the DSR is read in directly by the Audio/COMAND control panel.

The Electronic Stability Program control unit receives the signals over the chassis FlexRay, electronic ignition lock control unit, user interface CAN, head unit and the telematics CAN from the Audio/COMAND control panel. The Electronic Stability Program control unit regulates the required speed setting using interventions by the brake system. While driving downhill, the speed setting can be varied during active speed regulation via the cruise control lever.

If the driver accelerates the vehicle by pressing the accelerator pedal while the function is active, the downhill speed regulation switches to passive mode.

If the vehicle speed is v > 30 km/h when the accelerator pedal is not pressed, it is actively regulated to the configured speed setting. If the driver then accelerates the vehicle using the accelerator pedal during an active function to a speed of v > 30 km/h, the downhill speed regulation switches off automatically and the LED in the Downhill Speed Regulation switch goes out. A message also appears on the instrument cluster and a warning tone is emitted.

If the speed regulation for downhill driving is switched off manually via the Downhill Speed Regulation button, similarly, a message appears on the instrument cluster. A warning tone does not sound in this case.

Additional function requirements for off-road program 

Function sequence for off-road program (on model 253, with CODE 430 (Off-road package)) 

The off-road mode partial function is comprised of the following subfunctions:

Function sequence for activation of off-road program 

The off-road programs are activated using the On/Off-road menu button in the off-road operating panel. The off-road menu is shown on the audio/COMAND display and the driver can choose between the following off-road programs:

Function sequence for adaptation of the threshold values 

Through activation of the off-road programs

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 the appropriate signal to the rear SAM control unit via chassis FlexRay and interior CAN with electronic ignition lock control unit interface.

The rear SAM control unit actuates the left rear lamp unit, the right rear lamp unit and the center brake lamp with a flashing frequency of f = 5 Hz for the duration of the signal (at least t = 1 s). 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 again, the hazard warning system are automatically switched off again.

Additional function requirements - dry braking 

IMPORTANT The status of the windshield wiper system is transmitted by the front SAM control unit to the Electronic Stability Program control unit via interior CAN, electronic ignition lock control unit and chassis FlexRay.

Dry braking function sequence 

The dry braking function enhances the performance of the brakes on the front axle in wet driving conditions. The brake pads are applied cyclically for a short time (approx. 0.5 s) with a brake pressure p = 1 bar to remove the film of water from the brake disk. 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 pad 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 pads 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 quickly pressing down hard on the actuated brake pedal after coming to a standstill.

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 (except AMG vehicles) 

In driving mode, the ESP® function can be switched to passive using the left multifunction steering wheel button group and right multifunction steering wheel button group through the "Assist" menu and "ESP®" submenu in the instrument cluster.

The instrument cluster receives control signals from the multifunction steering wheel in the following way:

The instrument cluster then sends the "ESP_OFF" request to the Electronic Stability Program control unit via user interface CAN and chassis FlexRay with electronic ignition lock control unit interface. When the function is switched passive, the Electronic Stability Program warning lamp lights up in the instrument cluster. The control thresholds are raised when the ESP® is in passive mode. ABS cannot be deactivated. ESP® is always active during a brake application.

Function sequence for switching ESP® to passive (on AMG vehicles) 

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, the AMG ESP® Sport OFF button may only be pressed briefly. To switch off 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 left lower control panel and transmitted via lower control panel LIN, telematics CAN, head unit, user interface CAN, electronic ignition lock control unit and chassis FlexRay to the Electronic Stability Program control unit.

The operating modes are:

ESP® ON 

ABS, ASR and ESP® operate like they do in series production vehicles 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 

The ABS operates as on series production vehicles 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 ESP® trailer stabilization (with CODE 550 (Trailer hitch)) 

The ESP® trailer stabilization detects rocking motion in the tractor/trailer combination based on the yawing vibrations caused in the tractor vehicle by the trailer. If vehicle/trailer instability occurs, this is detected in the ADAPTIVE BRAKE on the basis of the signals from the supplemental restraint system control unit. The Electronic Stability Program control unit receives this information via the vehicle dynamics CAN.

IMPORTANT The ESP® trailer stabilization engages more sensitively if a trailer hitch is installed at the factory. Stabilization is ensured through standard intervention for retrofitted trailer hitches.

The ESP® trailer stabilization stabilizes the tractor/trailer combination by means of brake pressure requests on alternating sides of the front axle and, if necessary, slows down the tractor/trailer combination by reducing engine torque and by building up pressure at all wheels. Active vehicle/trailer stabilization does not change the critical speed.

Function sequence for PRE-SAFE® system (with code 23P (Driving Assistance package Plus)) 

The PRE-SAFE® system is activated in critical driving conditions, i.e. in a potential accident situation. The goal is to create the most favorable conditions possible for the occupants during the 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:

Function sequence for standstill control (SSC) 

The standstill control monitors the braking driver assistance system DISTRONIC PLUS (with ADAPTIVE BRAKE Premium system (with CODE 23P (Driving Assistance package Plus)) and the HOLD function below a speed of 3 km/h until the vehicle comes to a safe standstill. Within this vehicle speed range, the SSC is responsible for 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 systems. If vehicle rolling is detected, the brake pressure is increased until the vehicle is stationary again. In the case of vehicles with ADAPTIVE BRAKE premium system (with CODE 23P (Driving assistance package plus)), a leakage compensation function is also active in addition to the safe standstill. If the brake pressure measured by means of the circuit pressure sensors drops relative to the specified pressure request of the SSC, the specified pressure of the SSC is restored by means of an active pressure buildup.

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

Door contact plausibility check 

Plausibility checks are used to detect a fault along the signal path from the left front door rotary tumbler switch or right front door rotary tumbler switch (depending on the global country coding for right-hand or left-hand vehicles), read in by the left front door control unit or the right front door control unit and via interior CAN and chassis FlexRay, with the electronic ignition lock control unit 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.

SSK deactivation 

Deactivation of SSC is communicated internally in the Electronic Stability Program control unit and externally via chassis FlexRay. Activation of the driver assistance systems 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 the vehicle 

The vehicle is secured by the comfort securing system of the electric parking brake, which is prompted to lock by the SSC. After implementing the close request from the Electronic Stability Program control unit (except AMG vehicles) or from the electric parking brake control unit (with AMG vehicles), the vehicle is secured. The existing brake pressure at the wheels is reduced and the SSC 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 (on vehicles with automatic transmission) 

The safety strategy is implemented via the intelligent servo module for DIRECT SELECT. The Electronic Stability Program control unit sends a request to engage gear range "P" to the intelligent servo module control unit for DIRECT SELECT via chassis FlexRay, powertrain control unit and drive train CAN. The vehicle is secured once the intelligent servo module for DIRECT SELECT has engaged gear range "P" and following feedback to the Electronic Stability Program control unit. The existing brake pressure at the wheels is reduced and the SSK becomes inactive.

If the intelligent servo module for DIRECT SELECT 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 the chassis FlexRay and itself sends a request to the intelligent servo module for DIRECT SELECT. If the electronic ignition lock control unit does not receive feedback from the intelligent servo module for DIRECT SELECT within a defined time, the Emergency-P path is energized by the electronic ignition lock control unit after being enabled by the intelligent servo module for DIRECT SELECT and engagement of gear range "P" is forced by a spring mechanism in the intelligent servo module for DIRECT SELECT.

Safety strategy (on vehicles with manual transmission) 

The safety strategy on vehicles with manual transmission is subdivided into 3 stages:

The beeping is stopped immediately as soon as the driver deactivates the active driver assistance system.

Steer Assist function sequence 

Steer Assist is intended to help the driver achieve the optimal steering characteristics in critical situations. Steering assistance is provided with the aid of the electric power steering control unit and Electronic Stability Program control unit.

The following functions are performed here:

The current vehicle status is sensed by the Electronic Stability Program control unit. If necessary, the message "Steering assistance request" is sent via the chassis FlexRay to the electrical power steering control unit which actuates the electric power steering actuator motor accordingly.

Additional function requirements for Crosswind Assist 

Function sequence for Crosswind Assist 

The Crosswind Assist function assists the driver in the event of strong crosswinds and minimizes the vehicle's yaw response and the track offset. through course-correcting brake interventions. The Supplemental Restraint System control unit records the movement of the vehicle in the event of quickly changing winds and sends the signals to the Electronic Stability Program control unit via vehicle dynamics CAN. Besides, the Electronic Stability Program control unit processes the steering wheel angle provided by the steering wheel angle sensor via chassis FlexRay, which is read in by the steering column tube module control unit, the toothed rack position from the electrical power steering control unit, the wheel speeds and the brake pressures.

System fault display function sequence 

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 and sent via interior CAN, the electronic ignition lock control unit and user interface CAN to the instrument cluster.

IMPORTANT During semi-automatic parking and driving out of a parking space, the Electronic Stability Program control unit receives information about the remaining distance to the defined obstacle from the parking system control unit (with CODE 235 (Active Parking Assist)) over the chassis FlexRay. The Electronic Stability Program control unit calculates the required braking torque and actuates the traction system hydraulic unit accordingly upon reaching the maneuvering points or the target parking position. The vehicle is braked.

  Electrical function schematic for Adaptive Brake (ABR)   PE42.47-P-2050-97FBA 
  Overview of system components, Adaptive Brake (ABR)   GF42.47-P-9997RF 
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