GF42.47-P-0001FL Adaptive Brake (ABR), Function

GF42.47-P-0001FL Adaptive Brake (ABR), Function
MODEL 212.0/ 2

Function requirements, general
^ Circuit 61 ON
^ Adaptive brake (ABR) is functional

ABR, general
ABR assists the driver in dangerous situations which occur suddenly and thus serves active safety.
To this end, the Electronic Stability Program control unit (N30/4) (except code (233) DISTRONIC PLUS) or the Premium Electronic Stability Program control unit (N30/7) (with code (233) DISTRONIC PLUS) evaluates the data for the following components to monitor the driving situation at any given time:
- Yaw rate sensor for lateral and longitudinal acceleration (B24/15)
- Left front axle rpm sensor (L6/1)
- Right front axle rpm sensor (L6/2)
- Left rear axle rpm sensor (L6/3)
- Right rear axle rpm sensor (L6/4)
- Steering angle sensor (N49)
- Brake lights switch (S9/1)

There are 2 ABR variants in use:
^ ABR base system (except code (233) DISTRONIC PLUS)
^ ABR premium system (with code (233) DISTRONIC PLUS)

There are no differences between the variants with respect to the ABR subfunctions described below.

The system is made up of the following subfunctions:
^ Electronic Stability Program (ESP)
^ Electronic brake force distribution (EBV)
^ Emission test, roller dynamometer mode
^ Antilock brake system (ABS)
^ Acceleration skid control (ASR), electronic traction system (ETS)
^ Brake Assist (BAS)
^ BAS Plus, with code (233) DISTRONIC PLUS
^ ESP(R) trailer stabilization (Trailer Stability Assist (TSA)), (with code (550) Trailer hitch)
^ Hill Start Assist
^ Dry braking
^ Precharging, depending on accelerator pedal actuation
^ Precharging, depending on lateral acceleration
^ Start-off assist (HOLD function)
^ Deactivate ASR and ESP, except model 212 (with code (990) AMG vehicles), up to 31.5.10
^ Deactivate ASR and ESP, except model 212 (with code (990) AMG vehicles), as of 1.6.10
^ ASR and ESP ON, Sport or OFF, only with model 212 (with code (990) AMG vehicles)
^ Function sequence for Failed Boost (with code (B03) ECO start/stop function), model 212.0 with code (494) USA version as of 1.9.09, model 212.0 except code (494) USA version as of 1.12.09, model 212.2
^ Function sequence for Over Boost (with code (B03) ECO start/stop function), model 212.090 with code (494) USA version as of 1.9.09, model 212.090 except code (494) USA version as of 1.12.09, model 212.272
^ Function sequence - Standstill coordinator
^ 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 to correct any deviations. Furthermore, reduction of the drive torque takes place in order to increase directional stability and road adhesion.

The ESP control unit (except code (233) DISTRONIC PLUS) or the ESP Premium control unit (with code (233) DISTRONIC PLUS) processes the following measured quantities in order to determine the vehicle behavior:
- Yaw velocity
- Steering wheel angle
- Brake pressure
- Engine torque
- Transmission shift stage
- Lateral acceleration
A differentiation is made between the following vehicle characteristics:
^ 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. If the driver presses the accelerator pedal at this time, the drive torque will be reduced first.

If this is not enough or if the accelerator pedal is not depressed the incipient instability is prevented by brake application at up to 3 wheels as follows:
- Brake pressure buildup at rear wheel on inside of curve (stage 1)
- Stage 1 and in addition brake pressure buildup at rear wheel on outside of curve (stage 2)
- Stage 2 and in addition brake pressure buildup at front wheel on inside of curve (stage 3)

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 ESP control unit (except code (233) DISTRONIC PLUS) or Premium ESP control unit (with code (233) DISTRONIC PLUS) sends a drive torque reduction signal via the chassis CAN (CAN E) to the CDI control unit (N3/9) (with diesel engine) or ME-SFI [ME] control unit (N3/10) (with gasoline engine), which reduces engine power accordingly.
A pending shift operation is suppressed for the duration of control intervention.
For this purpose, the ESP control unit (except code (233) DISTRONIC PLUS) or ESP Premium control unit (with code (233) DISTRONIC PLUS) sends a signal via the chassis CAN to the CDI control unit (with diesel engine) or ME-SFI [ME] control unit (with gasoline engine), which sends the information via the drive train CAN (CAN C) to the electronic transmission-control control unit (N15/3) (with transmission 722.6) or to the fully integrated transmission control unit (Y3/8n4) (with transmission 722.9). The electronic transmission-control control unit (with transmission 722.6) or fully integrated transmission control unit (with transmission 722.9) suppresses the shift operation.

EBD [EBV]
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 stage and brake pressure at each wheel.
If the measured yaw velocity does not match the specified value, or if the determined side-slip angle is too large, the ESP control unit (except code (233) DISTRONIC PLUS) or ESP Premium control unit (with code (233) DISTRONIC PLUS) generates a signal to either increase or reduce brake force at the required wheel. The resulting forces stabilize the vehicle.

Emission test, roller dynamometer mode
For vehicle test purposes, the ABR can be set to roller dynamometer mode if the workshop menu is activated via the instrument cluster (A1) and the engine is then started. ESP, ABS and ASR are then switched passive. The Electronic Stability Program warning lamp (A1e41) and the antilock brake system indicator lamp (A1e17) in the instrument cluster light up. In addition, a message is displayed in the multifunction display (A1p13) of the instrument cluster. The dynamometer mode can also be activated using the Diagnosis Assistance System (DAS).

ABS
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 the signals from the rpm sensors indicate to the ESP control unit (except code (233) DISTRONIC PLUS) or ESP Premium control unit (with code (233) DISTRONIC PLUS) that a wheel has locked up, the brake pressure at the respective brake cylinder is reduced until the wheel starts turning again.

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. Any spinning of the drive wheels is picked up by the ESP control unit (except code (233) DISTRONIC PLUS) or ESP Premium control unit (with code (233) DISTRONIC PLUS) which reads the signals from the rpm sensors. Wheel spinning is countered by reduction of the drive torque.
For this purpose, the ESP control unit (except code (233) DISTRONIC PLUS) or Premium ESP control unit (with code (233) DISTRONIC PLUS) sends a drive torque reduction signal via the chassis CAN to the CDI control unit (with diesel engine) or ME-SFI [ME] control unit (with gasoline engine), which reduces engine power accordingly.
A check is continuously performed to establish whether the drive torque specified by the driver via the accelerator pedal sensor (B37) 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
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.

The ESP control unit (except code (233) DISTRONIC PLUS) or ESP Premium control unit (with code (233) DISTRONIC PLUS) does this by interpreting the degree of pressure rise in the brake system and initiates emergency braking if a certain triggering threshold is exceeded.

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.

ESP(R) trailer stabilization (TSA) (with code (550) Trailer hitch)
TSA detects pendular swinging motion in a tractor/trailer combination based on the yawing vibrations caused in the tractor vehicle by the trailer. The front SAM control unit with fuse and relay module (N10/1) routes the information to the chassis CAN.
This is received by the ESP control unit (except code (233) DISTRONIC PLUS) or by the Premium ESP control unit (with code (233) DISTRONIC PLUS).
If vehicle/trailer instability occurs, this is detected by the yaw rate, lateral and longitudinal acceleration sensor.
The ESP control unit (except code (233) DISTRONIC PLUS) or ESP Premium control unit (with code (233) DISTRONIC PLUS) receives this information via the vehicle dynamics CAN (CAN H).

No additional sensors are used on the trailer or trailer hitch.

TSA 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 torque and by building up pressure at all wheels.
The vehicle is stabilized only via the front axle. If heavy negative damping is detected, the system intervenes to decelerate the vehicle and stabilize the trailer.

If several TSA interventions occur in quick succession, the simple stabilization intervention is no longer allowed by the system, regardless of the damping detected.
This prevents the tractor/trailer combination from constantly driving at a critical speed and prevents the brake system from being subjected to too much stress due to interventions in quick succession.
Active vehicle/trailer stabilization does not change the critical speed.

Additional function requirements for the Hill Start Assist
^ Transmission not in position "N" (with transmission 722)
^ Vehicle not secured with parking brake
^ Incline detected with vehicle at standstill

Hill-starting assist
Hill Start Assist helps to prevent the vehicle rolling back when starting off in a forward gear range as the foot moves 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 information is sent via the vehicle dynamics CAN to the ESP control unit (except code (233) DISTRONIC PLUS) or the ESP Premium control unit (with code (233) DISTRONIC PLUS). The ESP control unit (except code (233) DISTRONIC PLUS) or ESP Premium control unit (with code (233) DISTRONIC PLUS) also reads the brake light switch directly to detect the status of the brake pedal.
The status of the parking brake is detected via the parking brake indicator switch (S12). This is read in directly by the front SAM control unit with fuse and relay module and its status sent over the chassis CAN to the ESP control unit (except code (233) DISTRONIC PLUS) or the Premium ESP control unit (with code (233) DISTRONIC PLUS).
The brake pressure applied by the driver is maintained in the brake cylinders by the traction system hydraulic unit (A7/3).

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
^ No brake intervention by a control system
^ Speed v > 30 km/h
^ Number of wiper cycles > 600
The switch status of the wiper system is sent by the front SAM control unit with fuse and relay module via the chassis CAN to the ESP control unit (except code (233) DISTRONIC PLUS) or ESP Premium control unit (with code (233) DISTRONIC PLUS).

Dry braking
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.
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.

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.

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.

Start-off assist (HOLD function)
The HOLD function assists the driver when starting off on a hill or during waiting times in traffic. The HOLD function is activated by briskly depressing the brake pedal at a standstill. The adjusted brake pressure is maintained until the driver depresses the brake pedal again rapidly or starts off.

Warning strategy (for vehicles with electronic selector lever module control unit (N15/5)), for transmission 722.6
If the HOLD function is activated and the driver wishes to exit the vehicle, the driver will not be able to withdraw the transmitter key (A8/1) from the electronic ignition lock (N73) control unit.
An acoustic and optical warning will be issued through the instrument cluster.

Safety strategy (for vehicles with intelligent servo module for DIRECT SELECT (A80)), with transmission 722.9
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.

Deactivate ASR and ESP, except model 212 (with code (990) AMG vehicles), up to 31.5.10
The ASR and ESP functions can be activated passively via the ESP button (S6/1s5) in the dashboard switch group (S6/1). The instrument panel switch group status is read via the instrument panel LIN (LIN 1) by the front SAM control unit with fuse and relay module and sent via the chassis CAN to the ESP control unit (except code (233) DISTRONIC PLUS) or ESP Premium control unit (with code (233) DISTRONIC PLUS). If the system is activated passively, the Electronic Stability Program warning lamp (A1e41) lights up in the instrument cluster.
The control thresholds are raised in the case of passive switching.
ABS cannot be deactivated. ESP is always active during a brake application.

Deactivate ASR and ESP, except model 212 (with code (990) AMG vehicles), as of 1.6.10
In driving mode the ASR and ESP functions can be switched passive with the left multifunction steering wheel button group (S110) and right multifunction steering wheel button group (S111) via the "Assist" menu and "ESP" submenu in the IC.
The IC receives control signals from the multifunction steering wheel (MFL) in the following way:
- Steering wheel electronics (N135)
- Steering LIN (LIN E1)
- Steering column tube module (N80)
- Chassis CAN

The instrument cluster then sends the "ESP_OFF" request over the chassis CAN to the ESP control unit (except code (233) DISTRONIC PLUS) or the Premium ESP control unit (with code (233) DISTRONIC PLUS).
If the functions are switched passive, the ESP warning lamp lights up in the instrument cluster.
The control thresholds are raised when the ASR and ESP functions are switched passive.
ABS cannot be deactivated. ESP is always active during a brake application.

ASR and ESP ON, Sport or OFF, only with model 212 (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 (S193/1) button. To switch between ESP ON and ESP
Sport mode, press the ESP OFF switch only briefly. When switching off the ESP, press the ESP Sport Off AMG button for t > 2.5 s. The ESP Sport Off AMG button status is read in by the transmission mode control unit (N145) and sent over the chassis CAN to the ESP control unit (except code (233) DISTRONIC PLUS) or the Premium ESP control unit (with code (233) DISTRONIC PLUS).
The operating modes are:
^ ESP ON
^ ESP SPORT
^ ESP OFF

ESP ON
ABS, ASR and ESP operate as on series production vehicles with adjusted control thresholds.
The Electronic Stability Program warning lamp and the ESP(R)/ASR OFF warning lamp (A1e32) in the instrument cluster are off, during an ESP intervention the Electronic Stability Program warning lamp flashes on and off.

ESP Sport
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 as with reduced intervention strength 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.

ESP OFF
ABS is configured for maximum deceleration. Ride comfort is of secondary importance.
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 system interventions are made.
The Electronic Stability Program warning lamp and the ESP(R)/ASR OFF warning lamp in the instrument cluster remain lit. The message "ESP OFF" appears in the instrument cluster.
All Pre-Safe functions are deactivated in ESP OFF mode.

Function sequence for Failed Boost (with code (B03) ECO start/stop function), model 212.0 with code (494) USA version as of 1.9.09, model 212.0 except code (494) USA version as of 1.12.09, model 212.2
The Failed Boost function serves to safeguard a sufficiently high brake pressure level in the system in the event of a shortage of brake boosting by the BAS brake booster.
If during a brake application by the driver, the brake vacuum pressure sensor (B64/1) (with code (B03) ECO start/stop function) recognizes that the BAS brake booster is not providing any driver assistance, then Failed Boost provides driver assistance through actuating the high pressure and return flow pump (A7/3m1). Hydraulic boosting occurs with a suitable boost factor.

Function sequence for Over Boost (with code (B03) ECO start/ stop function), model 212.090 with code (494) USA version as of 1.9.09, model 212.090 except code (494) USA version as of 1.12.09, model 212.272
If the brake booster reaches the limits of its pneumatic boost, the brake pressure is increased through actuation of the high pressure and return flow pump, thereby ensuring that the usual level of brake boost is then provided.

The function sequence for Failed Boost and the function sequence for Over Boost differ in terms of the triggering thresholds and hydraulic boost.

Function sequence - standstill coordinator
When Assist systems, such as the HOLD function for example, are activated and the driver status is unclear, the standstill coordinator requests that the vehicle be transferred to a secured condition.

The driver status is deemed to be unclear, if the driver door is open and the belt buckle of the drive seat belt is not inserted into the belt lock. Plugging the seat belt tongue into the seat belt buckle is detected by the driver seat belt buckle restraint system switch (S68/3). The supplemental restraint system control unit (N2/10) directly reads in the status of the driver seat belt buckle and belt warning switch and then sends the data over the chassis CAN to the ESP control unit (except code (233) DISTRONIC PLUS) or the Premium ESP control unit (with code (233) DISTRONIC PLUS).
The support systems cannot be operated.

System fault display
The driver is informed about the system status and about faults by the following displays:
- Antilock brake system indicator lamp (A1e17)
- Electronic Stability Program warning lamp
- Messages in multifunction display (A1p13)
- Brake fluid and parking brake warning lamp (A1e7)
Basic braking function without ABS is always available in case of failure of the ESP control unit (except code (233) DISTRONIC PLUS) or ESP Premium control unit (with code (233) DISTRONIC PLUS).

The status of the brake fluid level switch (S11) and the parking brake indicator switch is read by the front SAM control unit with fuse and relay module and sent via the interior CAN (CAN B) to the instrument cluster.