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

Model 238 

Up To Model Year 2021 

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• Engine running or drive train operational

ADAPTIVE BRAKE, general 

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

The Electronic Stability Program control unit actuates the ADAPTIVE BRAKE.

Depending on the equipment installed, various functions may request braking torque from the Electronic Stability Program control unit, that are implemented by the ADAPTIVE BRAKE:

• Active Brake Assist (with code 258 (COLLISION PREVENTION ASSIST))
• DISTRONIC distance pilot (with code 239 (DISTRONIC distance pilot) or code 23P (Driving assistance package))
• Emergency Stop Assist (with code 23P (Driving Assistance Package))
• Active Lane Keeping Assist (with CODE 23P (Driving assistance package))
• Active Blind Spot Assist (with CODE 23P (Driving assistance package))
• Rear-end PRE-SAFE® (with code 23P (Driving Assistance Package))
• Parking Pilot (with code 235 (PARKTRONIC Parking Pilot))

To implement the ADAPTIVE BRAKE function, the Electronic Stability Program control unit evaluates the following variables:

• Engine running or drive train operational

  The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" or "Drive train operational" signal over the drive train CAN, powertrain control unit and the chassis FlexRay to the Electronic Stability Program control unit.

• Wheel speeds, vehicle speed

  The wheel speeds are detected by the rpm sensors. The Electronic Stability Program control unit directly reads in the signals from the rpm sensors.

  The Electronic Stability Program control unit calculates the vehicle speed from the wheel speeds.

• Steering wheel angle

  The steering angle is recorded by the steering wheel angle sensor. The steering column tube module control unit reads in the signals from the steering wheel angle sensor directly and sends the steering wheel angle via chassis FlexRay to the Electronic Stability Program control unit.

• Yaw rate, lateral acceleration

  An acceleration sensor is integrated in the supplemental restraint system control unit which records the data on the vehicle's natural dynamics. The supplemental restraint system control unit sends this information via the vehicle dynamics CAN to the Electronic Stability Program control unit.

• Status of brake pedal

  The status of the brake pedal is detected by the brake lights switch. The Electronic Stability Program control unit directly reads in the status of the brake lights switch.

• Brake pressure

  The brake pressure is recorded by the master brake cylinder pressure sensor (except code 23P (Driving Assistance Package)) or from the front pressure sensor and from the rear pressure sensor (with code 23P (Driving Assistance Package)) in the traction system hydraulic unit. The Electronic Stability Program control unit reads in the signals from the pressure sensor directly.

• Engine torque

  The CDI control unit or the ME-SFI [ME] control unit sends information about the currently available engine torque via drive train CAN, powertrain control unit and chassis FlexRay to the Electronic Stability Program control unit.

• Engaged gear range (transmission 725)

  The fully integrated transmission control unit sends information about the engaged gear range via drive train CAN, powertrain control unit and chassis FlexRay to the Electronic Stability Program control unit.

• Turning angle, wheel angle

  The electrical power steering control unit sends information on the turning angle, wheel angle over the chassis FlexRay to the Electronic Stability Program control unit.

The Electronic Stability Program control unit actuates the corresponding control valves in the traction system hydraulic unit to implement the ADAPTIVE BRAKE function.

The traction system hydraulic unit contains the following components:

• Master brake cylinder pressure sensor (except code 23P (Driving Assistance Package))

  The master brake cylinder pressure sensor measures the brake pressure applied by the driver (master brake cylinder pressure).

• Front pressure sensor and rear pressure sensor (with code 23P (Driving Assistance Package))

  The two pressure sensors measure the pressure in the corresponding brake circuit.

• High pressure and return pump

  The self-priming high-pressure and return flow pump is pulse-actuated for pressure buildup and release for acceleration skid control interventions (ASR), control interventions by the Electronic Stability Program (ESP®) as well as for return flow in the case of control interventions by the anti-lock braking system (ABS).

• Pressure regulator valve

  The pressure regulating valves are used for pressure buildup, holding pressure and pressure reduction during ABS, ASR and ESP® closed-loop operation.

• Switchover valves

  During ASR and ESP® closed-loop operation, the switchover valves block the active high-pressure circuit with respect to the master brake cylinder.

• Ball valves

  The ball valves are opened during an ASR or ESP® pressure buildup phase to enable supply from the brake fluid reservoir via the high-pressure and return flow pump to the corresponding brake calipers.

The Electronic Stability Program control unit reads in the pressure sensor signals directly and actuates the high-pressure and return flow pump and the corresponding valves directly.

The ADAPTIVE BRAKE is used in two variants:

• Basic ADAPTIVE BRAKE (except code 23P (Driving Assistance Package))
• Premium ADAPTIVE BRAKE system (with code 23P (Driving Assistance Package))

ADAPTIVE BRAKE comprises the following functions:

• Electronic Stability Program (ESP®) 
• Electronic brake force distribution (EBD) 
• Dynamometer test mode 
• Torque Vectoring Brake 
• Anti-lock braking system (ABS) 
• Straight Line Control 
• Acceleration skid control (ASR), electronic traction system (ETS) 
• Brake Assist System (BAS) 
• Brake Assist System PLUS (BAS PLUS) (with CODE 23P (Driving assistance package)) 
• Change damper characteristics (with code 459 (Steel suspension with adjustable damping) or code 489 (AIR BODY CONTROL)) 
• Hill Start Assist 
• Flashing adaptive brake lights (except code 494 (USA version)) 
• Dry braking 
• Precharging, depending on accelerator pedal actuation 
• Precharging, depending on lateral acceleration 
• HOLD function 
• Switch ESP® to passive (model 238.361/461) 
• ESP® trailer stabilization (with CODE 550 (Trailer hitch)) 
• PRE-SAFE® system 
• Fail boost 
• Overboost 
• Standstill check 
• Steer Assist 
• Crosswind Assist 
• System fault display 

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 for this. Furthermore, the engine torque is reduced to increase the driving stability.

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

• Wheel speeds
• Yaw rate, lateral acceleration
• Steering wheel angle
• Brake pressure
• Engine torque
• Engaged gear range (transmission 725)

A differentiation is made between the following types of intervention:

• 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 three wheels:

• Brake pressure buildup at inside rear wheel (stage 1)
• 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 that leads to the vehicle turning in with a simultaneous speed reduction, leading to a considerable stabilizing effect. The Electronic Stability Program control unit also sends the "Reduce engine torque" request over the chassis FlexRay, electronic ignition lock control unit, periphery CAN, powertrain control unit and the engine CAN to the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit then reduces the engine power.

On vehicles with transmission 725 any imminent shift operation is suppressed during the control intervention function. The Electronic Stability Program control unit sends the "Downshift suppression" request over the chassis FlexRay, powertrain control unit and the drive train CAN to the fully integrated transmission control unit. The fully integrated transmission control unit suppresses the shift operation.

EBV 

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 steer 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, the transmission shift gear (transmission 725) and the 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 increases or reduces brake pressure at the relevant wheel. The resulting forces stabilize the vehicle.

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 indicator and the anti-lock braking system indicator light up in the instrument cluster. Additionally, a corresponding message is shown in the instrument cluster.

The instrument cluster sends the status of the dynamometer test mode to the Electronic Stability Program control unit over the user interface CAN, electronic ignition lock control unit and the chassis FlexRay. The Electronic Stability Program control unit then switches the ESP®, ABS and ASR to passive mode and sends the request to switch on the indicator lamps and to output a corresponding message over the chassis FlexRay, the electronic ignition lock control unit and the user interface CAN to the instrument cluster.

Roller dynamometer mode can also be activated via the diagnostic tester.

Torque Vectoring Brake 

The Torque Vectoring Brake function actively influences the yaw rate or the yaw acceleration through interventions by the brake system at the rear axle. 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 

The ABS prevents the wheels from blocking when braking and as a result maintains the steerability and driving stability during vehicle deceleration. If the Electronic Stability Program control unit detects a locking wheel on the basis of the signals from the front rpm sensors, it reduces the brake pressure at the corresponding wheel until the wheel begins to turn again.

Straight Line Control 

The Straight Line Control function prevents the vehicle from pulling to one side during straight-line braking. This ensures safe and stable vehicle handling. An increase in the yaw rate during straight-line braking is detected in the Supplemental Restraint System control unit using the signals of the acceleration sensor. By reducing the pressure individually at each wheel, a corresponding counter torque is generated and the vehicle is stabilized.

ASR, ETS 

The ASR and ETS functions prevent the drive wheels from spinning when driving. In addition, they result in improved driving stability with an increased traction potential over the entire vehicle speed range. The Electronic Stability Program control unit detects the spinning of the drive wheels using the signals of the rpm sensors. If a drive wheel spins, its drive torque is reduced. Targeted interventions by the brake system at the spinning wheel transfer the drive torque to the opposite wheel. If necessary, the engine torque is reduced. To do so, the Electronic Stability Program control unit sends the "Reduce engine torque" request over the chassis FlexRay, powertrain control unit and engine CAN to the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit then reduces the engine power. A check is continuously performed of whether the drive torque specified by the driver can be permitted again, e.g. due to an improvement in road surface adhesion.

BAS 

The BAS function detects emergency braking situations based on rapid actuation of the brake pedal and increases the brake pressure if necessary 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.

BAS PLUS (with CODE 23P (Driving assistance package)) 

The BAS PLUS function increases the brake pressure depending on the speed of the brake pedal actuation and the distance of the vehicle driving in front.

Change damper characteristics (with code 459 (Steel suspension with adjustable damping) or code 489 (AIR BODY CONTROL)) 

The change in damper characteristics enables dynamic driving style while simultaneously preventing the vehicle from tilting over.

Depending on the driving situation, the Electronic Stability Program control unit requests a firm or a soft damper characteristic (transmission mode) in the adaptive damping system control unit or the AIR BODY CONTROL, control unit. The Electronic Stability Program control unit sends the corresponding request over the chassis FlexRay to the adaptive damping system control unit or the AIR BODY CONTROL, control unit.

Hill Start Assist 

The Hill-Start Assist prevents the vehicle from rolling back when driving off when the driver switches from the brake pedal to the accelerator pedal. The brake pressure applied by the driver is retained in the brake system.

If the Electronic Stability Program control unit detects an uphill or downhill gradient when the vehicle is at a standstill that could cause the vehicle to roll backwards, it automatically actuates the Hill-Start Assist. 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.

Following release of the brake pedal and detection of a start-off request, reduction of the brake pressure is controlled by means of the 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 operate the brake pedal, the pressure in the brake system is reduced after 1 s.

The CDI control unit or the ME-SFI [ME] control unit sends information about the accelerator pedal position via drive train CAN, powertrain control unit and chassis FlexRay to the Electronic Stability Program control unit.

In the following situations, the Hill-Start Assist is immediately interrupted:

• Engine is switched off, unless the engine is switched off by the ECO start/stop function
• Driver terminates the start-off operation by fully releasing the accelerator pedal
• Gear change of forward/reverse gear
• Gear change from "N" (transmission 725)
• Electric parking brake active
• Vehicle in skidding movement

In the following situations, the Hill-Start Assist is non-functional:

• Starting off on a level road or on a downhill gradient
• Transmission in position "N" (transmission 725)
• Electric parking brake active
• ESP® defective
• Vehicle in skidding movement

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

• Vehicle speed above 50 km/h
• Deceleration of more than 7.5 m/s2
• BAS activated
• ABS controls both front wheels

Flashing adaptive brake lights (except code 494 (USA version)) 

In the event of emergency braking, the Electronic Stability Program control unit sends a corresponding signal via chassis FlexRay, electronic ignition lock control unit and interior CAN to the rear SAM control unit.

The rear SAM control unit then actuates for the duration of the signal (for at least 1 s) all the brake lights on the vehicle at a frequency of 5 Hz. If the vehicle comes to a standstill from a speed in excess of 70 km/h (not urban traffic), the brake lights 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 

• No intervention by the brake system through a driver assistance system (with code 23P (Driving Assistance Package))
• Vehicle speed above 30 km/h
• Windshield wiper system ON

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

Dry braking 

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

Precharging, depending on accelerator pedal actuation 

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 recognized, the system assumes that the driver intends to brake. The function is activated and a brake pressure of 2 to 3 bar is generated.

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.

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.

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 message in the instrument cluster.

The HOLD function can be switched on under the following conditions:

• Vehicle at rest
• Seat belt fitted and driver door closed
• Selector lever not in position "P" (transmission 725)
• Engine running or switched off by the ECO start/stop function
• DISTRONIC Distance Pilot not active (with code 23P (Driving Assistance Package))
• Electric parking brake not active
• No shutoff through standstill control
• Vehicle not in skidding movement

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 automatically switched off under the following conditions:

• Accelerator pedal is operated (except in position "N" (transmission 725))
• Selector lever moved to position "P" (transmission 725)
• Brake pedal is depressed again with a certain pressure, the "HOLD" status message disappears in the instrument cluster
• Electronic parking brake active
• DISTRONIC Distance Pilot is activated (with code 23P (Driving Assistance Package))
• Brake pedal is operated and vehicle is in skidding movement

Switch ESP® to passive (model 238.361/461) 

The ESP® function can be switched to passive mode using the "Assistance" menu and the "ESP®" submenu in the head unit when in driving mode.

The head unit then sends the "ESP_OFF" request over the user interface CAN, electronic ignition lock control unit and chassis FlexRay to the Electronic Stability Program control unit. If the ESP® function is switched to passive, the Electronic Stability Program warning indicator comes on in the instrument cluster. The Electronic Stability Program control unit sends the "Actuate warning indicator" request over the chassis FlexRay, electronic ignition lock control unit and the user interface CAN to 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.

Additional function requirements for ESP® trailer stabilization (with code 550 (Trailer hitch)) 

• Trailer detected

The trailer recognition control unit sends the Trailer detected status via interior CAN, electronic ignition lock control unit and chassis FlexRay to the Electronic Stability Program control unit.

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. 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.

If tractor/trailer instability occurs, this is detected through the acceleration sensor signals from the supplemental restraint system control unit.

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.

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 into 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

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 Electronic Stability Program control unit reads in the signals from the brake vacuum sensor directly.

The fail boost function performs hydraulic brake boosting using a suitable boost factor and for this purpose actuates the corresponding components in the traction system hydraulic unit.

Overboost 

Like the fail boost function, the over boost function ensures brake boosting. The over boost function is activated if the pneumatic brake booster can no longer adequately support driver braking because of a brief sub-optimal vacuum level.

Unlike fail boost, over boost represents a normal operating state. There is no system error in the vacuum supply.

This briefly reduced vacuum level operating state can occur, for example, in the following cases:

• directly after engine start
• Driving at high altitude with low air pressure
• high frequency brake actuation

The over boost function performs hydraulic brake boosting using a suitable boost factor and for this purpose actuates the corresponding components in the traction system hydraulic unit.

Standstill check 

The standstill control monitors the braking driver assistance systems below a speed of 10 km/h until the vehicle comes to a safe standstill. Within this vehicle speed range the standstill control is responsible for ensuring the vehicle is brought to a safe standstill when a safety event arises.

When the vehicle is at a safe standstill, the standstill control's rolling monitoring function is requested by the driver assistance systems. If the start of a vehicle rolling motion is detected the brake pressure is increased until the vehicle comes to a standstill again. On vehicles with CODE 23P (Driving Assistance package), leakage compensation is also active during safe standstill. If the brake pressure measured by the circuit pressure sensor system compared to the standstill control's specified pressure request, the pressure is increased again.

Securing the vehicle using the standstill control 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)

  The left front door control unit sends the status of the left front door (open or closed) via interior CAN, electronic ignition lock control unit and chassis FlexRay to the Electronic Stability Program control unit. The supplemental restraint system control unit sends the status of the seat belt via vehicle dynamics CAN to the Electronic Stability Program control unit.

• Ignition OFF (circuit 15 OFF)

  The electronic ignition lock control unit sends the status of circuit 15 over the chassis FlexRay to the Electronic Stability Program control unit.

• Engine OFF, unless the engine has been switched off by the ECO start/stop function

  The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" or "Drive train operational" signal over the drive train CAN, powertrain control unit and the chassis FlexRay to the Electronic Stability Program control unit.

• Undervoltage or overvoltage (except undervoltage during a hot start)

  The front SAM control unit sends information on the on-board electrical system power status over the interior CAN, electronic ignition lock control unit and the chassis FlexRay to the Electronic Stability Program control unit.

• Because of a request to secure the vehicle issued by the a driver assistance system (with code 258 (COLLISION PREVENTION ASSIST) or code 239 (DISTRONIC Distance Pilot) or code 23P (Driving Assistance Package))
• ESP® and FlexRay faults that result in a temporary or permanent shutoff
• Standstill control that results in a temporary or permanent shutoff
• After a defined hydraulic holding period of 10 minutes

Door contact plausibility check 

The plausibility check is used to detect a fault in the signal path. If, as the result of an electrical or mechanical fault, "Driver door closed" is wrongly detected although the driver door is open, this is detected by the door contact plausibility check and a corresponding fault is stored in the Electronic Stability Program control unit.

Standstill control shutoff 

Deactivation of the standstill control is communicated internally in the Electronic Stability Program control unit and externally over the chassis FlexRay. Activation of the driver assistance systems is no longer possible. Securing of the vehicle is additionally requested immediately if the standstill control is shut off and a driver assistance system is active.

Securing the vehicle 

The vehicle is secured to match the given situation by engaging gear range P (transmission 725) or by applying the electric parking brake. The brake pressure applied at the wheels is reduced and the standstill control is switched to 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 standstill control, the electric parking brake is detected as being defective and, if necessary, gear range P (transmission 725) (Safety strategy) is requested.

Safety strategy, engage "P" or Emergency-P path request (transmission 725) 

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 over the chassis FlexRay, powertrain control unit and the 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 brake pressure applied at the wheels is reduced and the standstill control is switched to 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 within a specified period of time from the fully integrated transmission control unit, the Emergency-P path is energized after being enabled through the fully integrated transmission control unit by the electronic ignition lock control unit. Gear range "P" is forcibly engaged through a spring mechanism.

Steer Assist 

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 Electronic Stability Program request sends a "Steer Assist" request over the chassis FlexRay to the electrical power steering control unit.

Additional function requirements for Crosswind Assist 

• Vehicle speed 80 to 220 km/h
• Straight-ahead driving or slight cornering

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 Electronic Stability Program control unit uses the following signals to determine a wind interference (e.g. wind gusts) which is reacted to with a one-sided brake intervention:

• Vehicle speed
• Yaw rate, lateral acceleration
• Steering wheel angle
• Turning angle, wheel angle

System fault display 

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

• Anti-lock braking system indicator
• Parking brake indicator
• Electronic Stability Program warning indicator
• Brake system warning indicator
• Messages in the instrument cluster

If the Electronic Stability Program control unit fails, basic braking without ABS is always available. The Electronic Stability Program control unit sends the request to display system faults over the chassis FlexRay, electronic ignition lock control unit and the user interface CAN to the instrument cluster.

The status of the brake fluid level switch is read in by the front SAM control unit and sent over the interior CAN, electronic ignition lock control unit and the user interface CAN to the instrument cluster.

	Electrical function schematic for ADAPTIVE BRAKE		PE42.47-P-2051-97DCA
	Overview of system components of ADAPTIVE BRAKE		GF42.47-P-9996FH