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

MODEL 218 as of model year 2014 

Fig 1: Adaptive Brake Block Diagram
G10083101Courtesy 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 (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) evaluates the data from the following components in order to determine 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 (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) processes the following measured quantities in order to determine the vehicle's behavior:

A distinction is made between the following vehicle characteristics:

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 (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) sends a signal to reduce the drive torque via chassis CAN 1 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 (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) sends a signal via chassis CAN 1 to the CDI control unit (with diesel engine) or the ME-SFI control unit (with gasoline engine) which sends the information via the drive train CAN to the fully integrated transmission control unit. The fully integrated transmission control unit suppresses the shift operation.

EBD function sequence 

EBD [EBV] 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 the determined side-slip angle is too large, the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) generates a signal to increase the brake force or to reduce the brake force for the corresponding 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. In addition, a message is displayed in the multifunction display of the instrument cluster. The roller dynamometer mode can also be activated via Xentry Diagnostics.

ABS function sequence 

ABS prevents the wheels from locking up when braking and as a result maintains the steerability and directional stability and road adhesion during vehicle deceleration.

If a locked wheel is detected by the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or by the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) on the basis of the signals from the rpm sensors, the brake pressure at the corresponding brake cylinder is reduced 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 via the signals from the rpm sensors by the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or by the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)). Wheel spinning is countered by reduction of the drive torque.

For this purpose, the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) sends a signal to reduce the drive torque via chassis CAN 1 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 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 

BAS detects emergency braking situations from rapid actuation of the brake pedal and, if necessary, increases the brake pressure in order to achieve maximum possible deceleration.

For this purpose, the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) evaluates the degree of pressure rise in the brake system and, if a certain triggering threshold is exceeded, initiates emergency braking.

Function sequence for BAS PLUS, with CODE 233 (DISTRONIC 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.

Additional function requirements for the Hill Start Assist 

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 when the vehicle is at a standstill an incline is detected via the yaw rate sensor for lateral and longitudinal acceleration which would cause rolling in the opposite direction to the gear range engaged.

This is sent via the vehicle dynamics CAN to the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)).

In addition, the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) also reads in the brake light switch directly and thus detects the status of the brake pedal.

The status of the parking brake is detected through the parking brake indicator switch. This switch is read in by the front SAM control unit with fuse and relay module directly and its status is sent via chassis CAN 1 to the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)).

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

Once the brake pedal is released, the brake pressure is modulated based on the downward torque due to slope, braking torque and drive torque.

Once there is sufficient starting torque, the function is deactivated and the vehicle drives off.

However, if the driver does not actuate the accelerator pedal, the pressure in the brake cylinders is released after t = 1 s.

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 (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)).

Dry braking function sequence 

Dry braking enhances the performance of the brakes on the front axle in wet driving conditions. The brake pads are applied cyclically for t = 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.

IMPORTANT In order to adapt the calculated triggering threshold of the accelerator pedal gradient to 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 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 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 can be achieved.

Emergency braking is detected from the release gradient of the accelerator pedal, which is formed from the accelerator pedal position. 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.

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 and 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 depresses the brake pedal again or drives off. Pressure reduction when starting off is performed by the standstill coordinator according to the respective situation.

The HOLD function is deactivated automatically if:

Safety strategy 

If the HOLD function is activated and if the driver wishes to leave the vehicle, the position "P" is automatically engaged by the intelligent servo module for DIRECT SELECT when the vehicle is at a standstill and the transmitter key removed.

A warning is issued on the instrument cluster.

Function sequence for ASR and ESP® passive switching, except CODE 990 (AMG vehicles) 

The ASR and ESP® functions can be switched to passive mode in the "Assist" menu and the "ESP" submenu of the instrument cluster using the left multifunction steering wheel button group and the right multifunction steering wheel button group. The instrument cluster receives control signals from the multifunction steering wheel (MFL) in the following way:

The instrument cluster then sends the "ESP OFF" request via chassis CAN 1 and chassis CAN 2 to the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)).

If the system is switched passive, the Electronic Stability Program warning lamp lights up in the instrument cluster.

The control thresholds are raised in the case of passive switching.

IMPORTANT ABS cannot be deactivated. ESP® is always active during a brake application.

Function sequence for ASR and ESP ON, ESP Sport or ESP OFF, with CODE 990 (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 mode, press the ESP OFF switch only briefly. To switch off the ESP®, the AMG ESP Sport Off button must be pressed for t > 2.5 s. The status of the AMG ESP Sport Off button is read in by the transmission mode control unit and sent via chassis CAN 1 to the Premium 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 remains lit; it flashes during ESP® intervention. The message "ESP SPORT" appears in the instrument cluster.

switch 

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 are made.

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

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

Function sequence for SSK 

The standstill coordinator monitors the braking driver assistance systems DISTRONIC PLUS (with ADAPTIVE BRAKE premium system (with CODE 233 (DISTRONIC PLUS)) and HOLD function below a speed of 3 km/h until the vehicle has come 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 SSK is requested by the driver assistance systems. If vehicle rolling is detected, the brake pressure is increased until the vehicle is stationary again. On vehicles with the ADAPTIVE BRAKE premium system (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)), a leakage compensation function is also active during the safe standstill condition. If the brake pressure measured by means of the circuit pressure sensors drops relative to the specified pressure request of the SSK, the specified pressure of the SSK is restored by means of an active pressure buildup.

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

Door contact plausibility check 

The plausibility check detects any faults 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 drive vehicle), read in by the left front door control unit or right front door control unit and via the interior CAN and chassis CAN 1 to the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)). 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 in the SSC and a corresponding fault is stored in the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)).

SSK deactivation 

Deactivation of the SSC is signaled internally in the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) and externally via chassis CAN 1. 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.

Sliding 

When the vehicle is stationary, the SSK monitors whether the vehicle is sliding. Activation of the driver assistance systems is not permitted during this time. The active driver assistance systems must deactivate when the brake pedal is depressed and the vehicle is sliding.

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

The safety strategy is implemented via the intelligent servo module for DIRECT SELECT. The Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) sends a request to engage gear range "P" via chassis CAN 1 and the drive train CAN with the CDI control unit interface (with diesel engine) or ME-SFI control unit interface (with gasoline engine) to the control unit of the intelligent servo module for DIRECT SELECT. The vehicle is regarded as secured after gear range "P" has been engaged by the intelligent servo module for DIRECT SELECT and after feedback has been sent to the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)).

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.

Steer Assist function sequence 

Steer Assist is intended to help the driver achieve the optimal steering characteristics in critical situations. The Steer Assist function is realized with the aid of the electric power steering control unit and by means of the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)).

The following functions are performed here:

The current driving status is acquired by the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or by the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)). If necessary, the message "Steering assistance request" is sent via chassis CAN 1 and chassis CAN 2 to the electrical power steering control unit which actuates the electric power steering actuator motor accordingly.

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 (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) fails, basic braking without ABS is always available.

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

IMPORTANT In the case of semi-automatic parking space entry and exit, the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) receives the information about the remaining distance to the defined obstacle from the parking system control unit (N62) (with CODE 235 (Active Parking Assist)) via chassis CAN 1 and chassis CAN 2 with the front SAM control unit with fuse and relay module interface. The Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) calculates the required braking torque and actuates the traction system hydraulic unit accordingly when the maneuvering points or the target parking position are reached. The vehicle is braked.

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