Adaptive Brake Function - GF42.47-P-0002FG
Model 213 (except 213.050)
up to model year 2021
Block diagram as of 01.06.2018
Block diagram up to 31.05.2018
Function requirements, general
- Drive train operational
- Engine running.
- ADAPTIVE BRAKE functional
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:
- Left front axle rpm sensor
Additional function requirements - dry braking
- No intervention by the brake system through management system
- Speed v > 30 km/h
- Windshield wiper system switched on
The status of the windshield wiper system is sent from the front SAM control unit to the Electronic Stability Program control unit via interior CAN, electronic ignition lock control unit and suspension FlexRay.
Dry braking function sequence
- Right front axle rpm sensor
- Left rear axle rpm sensor
- Right rear axle rpm sensor
- Steering wheel angle sensor
- Stop lamp switch
ADAPTIVE BRAKE is available in 2 variants:
- ADAPTIVE BRAKE Basic system (except code 23P (Driving Assistance Package) and except code P20 (Driving Assistance Plus Package))
- ADAPTIVE BRAKE Premium system (with code 23P (Driving Assistance Package) or with code P20 (Driving Assistance Plus Package))
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 Electronic Stability Program (ESP®)
- Electronic brake force distribution (EBD) function sequence
- Function sequence of exhaust test, dynamometer test mode
- Function sequence for Torque Vectoring Brake
- Antilock brake system (ABS) function sequence
- Function sequence for acceleration skid control (ASR), electronic traction system (ETS)
- Function sequence for Brake Assist System (BAS)
- Function sequence for Brake Assist System PLUS (BAS PLUS) (with code 23P (Driving Assistance Package) or with code P20 (Driving Assistance Plus Package))
- Hill Start Assist function sequence
- Function sequence for adaptive brake lights flashing (except with code 494 (USA version))
- Dry braking function sequence
- Function sequence for precharging dependent on accelerator pedal operation
- Function sequence for precharging depending on lateral acceleration
- Function sequence for HOLD function
- Function sequence for switching ESP® to passive mode
- Function sequence for ESP® trailer stabilization (with code 550 (Trailer hitch))
- Function sequence for PRE-SAFE® system (with code 23P (Driving Assistance Package) or with code 292 (PRE-SAFE® Impulse side))
- Function sequence for standstill control (SSC)
- Steer Assist function sequence
- Function sequence for Crosswind Assist
- System fault display function sequence 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:
- Yaw velocity
- Steering wheel angle
- Brake pressure
- Engine torque
- Transmission stage
- Lateral acceleration
- Wheel speed
Differentiation is made between the following intervention types:
- Intervention in the case of oversteer
- Intervention in the case of understeer 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:
- Brake pressure buildup at inside rear wheel (stage 1)
The dry braking function enhances the performance of the brakes in wet driving conditions. Cyclic 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 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 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.
In order to adapt the calculated activation 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
In order to achieve the required braking power at the corresponding wheel as quickly as possible in the event of ESP® intervention, the brake pads are applied to the brake disks of the front axle during dynamic cornering to close the air gap between the brakepad and the brake disk.
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:
- The vehicle is stationary.
- The seat belt is inserted or when the driver door is closed.
- The selector lever is not in the "P" position.
- the engine is running or has been switched off by the ECO start/stop function.
- DISTRONIC PLUS is not active (with ADAPTIVE BRAKE Premium system (with code 23P (Driving Assistance Package) or with code P20 (Driving Assistance Plus Package))).
- The electronic parking brake is not applied or it is in the process of being applied.
- There is no shutoff in the standstill control.
- The vehicle is not sliding.
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
- The accelerator pedal is operated (except in the "N" position).
- The selector lever is set to position "P" (with automatic transmission).
- The brake pedal is depressed again with a certain pressure until the "HOLD" status line disappears in the instrument cluster.
- The electronic parking brake is applied.
- DISTRONIC PLUS is activated.
- The brake pedal is depressed and the vehicle is sliding.
Function sequence for switching ESP® to passive mode
When in driving mode, the ESP® function can be switched to the passive mode using the multifunction steering wheel instrument cluster button group through the "Assistance" menu and the "ESP®" submenu of the instrument cluster.
The instrument cluster multifunction steering wheel button group sends the operation signals over the following path: Steering wheel electronics →
Steering wheel CAN (as of 01.06.2018) or steering LIN (up to 31.05.2018) →
Steering column tube module control unit →
Chassis FlexRay →
Electronic ignition lock control unit →
User interface CAN →
Instrument cluster
The instrument cluster then sends the "ESP_OFF" request to the Electronic Stability Program control unit via user interface CAN and
- Stage 1 and in addition brake pressure buildup at outside rear wheel (stage 2)
- Stage 2 and in addition brake pressure buildup at inside front wheel (stage 3)
Depending on the brake force a torque arises which leads to the vehicle turning in with a simultaneous speed reduction, leading to a considerable stabilizing effect. The Electronic Stability Program control unit sends a signal to reduce the drive torque via the suspension 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 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 via the suspension FlexRay, the powertrain control unit and drive train CAN to the fully integrated 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 determined 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. ESP®, ABS and ASR are then switched to passive.
The Electronic Stability Program warning message and the anti-lock braking system control message light up in the instrument cluster. A corresponding message is also displayed 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 controllably 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 a reduction of the drive torque.
For this purpose, the Electronic Stability Program control unit sends a signal requesting a reduction in drive torque via the suspension FlexRay, powertrain control unit and engine CAN to the CDI control unit (with diesel engine) or the ME-SFI 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 over 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.
suspension FlexRay with electronic ignition lock control unit interface.
If the function is switched to passive, the Electronic Stability Program warning message 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 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 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.
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) or with code 292 (PRE-SAFE® Impulse side))
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:
- Panic post-braking (the driver's wish for deceleration is greater than physically possible)
- Pronounced oversteer (breaking away of rear area of vehicle in combination with major ESP® control intervention functions)
- Severe understeer (the vehicle pushes powerfully for a longer time over the front wheels)
- Rapid steering movements that suggest a shock reaction of the driver which can also lead to vehicle instabilities.
Function sequence for standstill control (SSC)
The standstill control monitors the braking driver assistance system below a speed of 10 km/h until the vehicle comes to 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 vehicles with ADAPTIVE BRAKE Premium system (with code 23P (Driving Assistance Package) or with code P20 (Driving Assistance Plus Package)), a leakage compensation function is also active during a 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:
- Driver is detected as absent (the driver door is open and the driver belt buckle is not fastened)
- Engine OFF, unless the engine has been switched off by the ECO start/stop function
- Undervoltage and overvoltage (except undervoltage during a hot start)
- Request for securing the vehicle (e.g. DISTRONIC PLUS)
- ESP® and FlexRay faults which result in temporary deactivation.
- SSC monitoring events that result in temporary or permanent deactivation.
- Expiry of the defined hydraulic holding period of 10 min
Door contact plausibility check
The plausibility check detects any faults along the signal path from the left front door microswitch first detent position or the right front door microswitch first detent position (depending on global national coding for right-hand or left-hand drive vehicle), read in by the left front door control unit or the right front door control unit and sent over the interior CAN and the suspension 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
BAS function sequence
In order to achieve maximum deceleration, BAS detects emergency braking situations based on a rapid actuation of the brake pedal and, if necessary, increases the brake pressure. To do so, the Electronic Stability Program control unit evaluates the increase in pressure in the brake system and initiates an emergency stop if a certain activation threshold is exceeded.
Function sequence for BAS PLUS (with code 23P (Driving Assistance Package) or with code P20 (Driving Assistance Plus Package))
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 triggered automatically if the Electronic Stability Program control unit detects uphill or downhill gradients when the vehicle is stationary which would cause the vehicle to roll in the opposite direction to the engaged gear range. 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 engine is switched off, unless the engine is switched off by the ECO start/stop function.
- The driver terminates the pulling away procedure by fully releasing the accelerator pedal.
- A forward/reverse gear change is performed.
- A gear change is made to selector lever position "N".
- The electronic parking brake is applied.
- The vehicle is slipping.
The Hill-Start Assist does not function, if
- The vehicle is driven off on a level road or on a downhill gradient.
- The transmission is in selector lever position "N".
- The electronic parking brake is applied.
- ESP® is malfunctioning.
- The vehicle is slipping.
Additional function requirements for adaptive brake lights flashing (except with code 494 (USA version))
- Vehicle speed> 50 km/h
- Deceleration 7.5 m/s2
- BAS activated
- ABS controls both front wheels.
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 the suspension FlexRay and the interior CAN with the 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 5 Hz for the duration of the signal (at least 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, the hazard warning system is automatically switched off again.
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 SSC is communicated internally in the Electronic Stability Program control unit and externally via the suspension 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 electronic parking brake, which is prompted to lock by the SSC. After the locking request has been implemented by the Electronic Stability Program control unit, 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 electronic parking brake within a defined time or the electronic parking brake signals a system fault to the SSC, the electronic 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 securing strategy is performed via the fully integrated transmission control unit. The Electronic Stability Program control unit transmits a request to engage gear range "P" to the fully integrated transmission control unit via the suspension FlexRay, powertrain control unit and drive train CAN. The vehicle is secured once the fully integrated transmission control unit 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 SSC becomes inactive.
If the fully integrated transmission control unit 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 suspension FlexRay and itself transmits a request to the fully integrated transmission control unit. If the electronic ignition lock control unit does not receive any feedback from the fully integrated transmission control unit within a defined time, the Emergency-P path is energized by the electronic ignition lock control unit following enabling by the fully integrated transmission control unit, and engagement of gear range "P" in the fully integrated transmission control unit is forced by a spring mechanism.
Safety strategy (on vehicles with manual transmission)
The safety strategy on vehicles with manual transmission is subdivided into 3 stages:
- Stage 1
In the event of incorrect operation or a system error, the warning message "Brake Immediately!" is displayed on the instrument cluster.
- Stage 2
The 2nd stage additionally warns the driver by means of an acoustic signal (beep).
- Stage 3
This beeping becomes louder in stage 3.
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:
- Driver support through countersteering for a vehicle with oversteer
- Driver support for braking on varying road surfaces
The current vehicle status is sensed by the Electronic Stability Program control unit. If necessary, the message "Steering assistance request" is sent via the suspension FlexRay to the electrical power steering control unit which actuates the electric power steering actuator motor accordingly.
Additional function requirements for Crosswind Assist
- Vehicle speed 80 to 220 km/h
- Straight-ahead driving or slight cornering
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 the suspension 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 messages in the instrument cluster:
- Anti-lock braking system control message
- Parking brake control message
- Electronic Stability Program warning lamp
- Brake system warning message
If the Electronic Stability Program control unit fails, basic braking without ABS is always available.
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.
Model 213 (except 213.050) up to model year 2021 with code 235 (Active Parking Assist)
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 via the suspension 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.
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