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

GF42.47-P-0001CE Adaptive Brake (ABR), Function
MODEL 204.0 /2 (except 204.077 /277) as of model year 2009 /modification year 08
MODEL 204.0 /2 as of model year 2012 /YoM 11 model refinement package
MODEL 204.3 (except 204.377)
MODEL 204.9

Function requirements, general
^ Engine running
^ Drivetrain ready
^ Adaptive brake (ABR) is functional

Adaptive Brake (ABR), general
ABR assists the driver in dangerous situations which occur suddenly and thus serves active safety.
To do so, the Electronic Stability Program control unit (N30/4) evaluates the data from the following components in order to detect the current driving situation:
- Yaw rate, lateral and longitudinal acceleration sensor (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)
- Stop lamp switch (S9/1)

ABR will be used as of 1.3.2011 (model 204.0/2) or as of 1.6.2011 (model 204.3) in 2 variants:
- ABR base system (except code (233) DISTRONIC PLUS)
- ABR premium system (with code (233) DISTRONIC PLUS)

Up to 28.2.2011 or 31.5.2011 and as from 1.6.2011 (model 204.9) only the ABR Basis ESP control unit system is used.

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)
^ Exhaust 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
^ Function sequence for downhill speed regulation (on model 204.9 with code (430) Off-road package)
^ Function sequence for off-road mode (on model 204.9 with code (430) Off-road package)
^ Dry braking
^ Precharging, depending on accelerator pedal actuation
^ Precharging, depending on lateral acceleration
^ Start-off assist (HOLD function)
^ Function sequence for PRE-SAFE(R) system, PRE-SENSE
^ Switch ASR and ESP to passive (model 204.9, model 204.0/2 up to 28.2.10)
^ Switch ASR and ESP to passive (model 204.3 as of 1.6.10, model 204.0/2 as of 1.3.10)
^ Failed Boost function sequence (with code (B03) ECO start/ stop function)
^ Over Boost function sequence (with code (B03) ECO start/ stop function)
^ 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 processes the following measured quantities to determine the vehicle behavior:
- Yaw velocity
- Steering wheel angle
- Brake pressure
- Engine torque
- Transmission stage
- Lateral acceleration

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. If the driver presses the accelerator pedal at this time, the drive torque will be reduced first.

If this is not enough or 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 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 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 sends a signal over the chassis CAN (CAN E) to reduce drive torque to the CDI control unit (N3/9) (with diesel engine) or the ME-SFI [ME] control unit (N3/10) (with gasoline engine), which then lowers the engine power accordingly. A pending shift operation is suppressed for the duration of control intervention.
To this end, the ESP control unit sends a signal over the chassis CAN to the CDI control unit (with diesel engine) or ME-SFI [ME] control unit (with gasoline engine), which then send the information over 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 control unit (Y3/8n4) (with transmission 722.9). The electronic transmission-control control unit (on transmission 722.6) or the 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 sideslip 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 yaw velocity measured does not match the specified value or if the determined sideslip angle is too large, the ESP control unit generates a signal to build up or reduce brake force for the relevant wheel. The resulting forces stabilize the vehicle.

Exhaust test/roller dynamometer mode
For vehicle test purposes, 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 a locking wheel is detected by the ESP control unit on the basis of the signals from the rpm sensors, the brake pressure is reduced at the appropriate brake cylinder until the wheel begins to turn 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. Spinning of the drive wheels is detected by the ESP control unit using the signals from the rpm sensors. Wheel spinning is countered by reduction of the drive torque.
To this end the ESP control unit sends a signal over the chassis CAN to reduce the drive torque to the CDI control unit (with diesel engine) or the 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 the maximum possible deceleration.

The ESP 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 (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 function is activated when a trailer is detected by the trailer recognition control unit (N28/1) and a signal sent via the interior CAN (CAN B) to the front SAM control unit with fuse and relay module (N10/1).

The front SAM control unit with fuse and relay module routes the signal to the chassis CAN, over which the signal is received by the ESP control unit. If pendulum motion of the vehicle/trailer occurs, this is detected by the yaw rate sensor for lateral and longitudinal acceleration. The ESP control unit receives this information over 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"
^ Vehicle not secured with parking brake
^ Incline detected with vehicle at standstill

Hill-starting assist
When starting off, Hill Start Assist prevents the vehicle rolling back opposite to the direction of the engaged gear during the time it takes for the driver to switch from brake to accelerator application.
The Hills Start Assist is triggered automatically if, when the vehicle is at a standstill, an upward or downward 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 transmitted to the ESP control unit via the vehicle dynamics CAN.
The ESP control unit also directly reads in the brake light switch thereby detecting the status of the brake pedal.
The status of the parking brake is detected via the parking brake indicator switch (S12). The switch status of the parking brake indicator switch is read in directly by the front SAM control unit with fuse and relay module and sent to the ESP control unit over the chassis CAN.
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.

When the torque is sufficient to move off, the function is deactivated and the vehicle starts 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 for speed control during downhill driving
^ v < 30 km/h

Function sequence for speed control during downhill driving
The downhill speed regulation serves to provide greater safety when driving on steep terrain.
The setting speed relevant to the speed regulation function for downhill driving can be adjusted in a range of v = 4 to 18 km/h in steps of 2 km/h in the corresponding menu in the instrument cluster.
The system is activated using the Downhill Speed Regulation switch (N72/1s24) in the upper control panel control unit (N72/1).
The activation is indicated by a light-emitting diode in the Downhill Speed Regulation switch.
The vehicle speed is then maintained in accordance with the speed setting (this is shown on the multifunction display of the instrument cluster).
While driving downhill, the speed setting can be varied via the cruise control lever (S40/4).
The request to activate the downhill speed regulation function is read in directly by the upper control panel control unit.
The upper control panel control unit transmits the signal on the interior CAN. The instrument cluster receives the signal and places this information along with the current speed setting on the engine compartment CAN.
The ESP control unit receives the signals and adjusts the vehicle speed to comply with the setting by means of brake interventions and appropriate requests to the engine control and transmission control systems.

If the driver accelerates the vehicle by pressing the accelerator pedal while the function is active, the downhill speed regulation switches to passive mode.
If the vehicle speed is v > 35 km/h when the accelerator pedal is not pressed, it is actively regulated to the configured setting speed.
If the driver accelerates the vehicle to a speed of v > 35 km/h using the accelerator pedal while the function is active, the downhill speed regulation switches off automatically and the LED in the Downhill Speed Regulation switch goes out. A message also appears on the multifunction display of the instrument cluster and a warning tone sounds. If the downhill speed regulation function is switched off manually using the Downhill Speed Regulation switch, a message also appears in the multifunction display of the instrument cluster. A warning tone does not sound in this case.

Additional function requirements for off-road mode
^ Circuit 61 ON
^ Gear range "N" active
^ v < 40 km/h

Function sequence for off-road mode
The off-road mode partial function is comprised of the following subfunctions:
^ Function sequence for activating the off-road mode
^ Function sequence for adaptation of the threshold values
^ Function sequence for engine torque support

Function sequence for activating off-road mode
The off-road mode is activated using the off-road program switch (N72/1s25) in the upper control panel control unit.
Activation is indicated by an illuminated light emitting diode in the off-road program switch. The off-road symbol also appears on the multifunction display of the instrument cluster.

Off-road mode is deactivated by pressing the off-road program switch again. The LED in the off-road program switch goes out and the indicator in the multifunction display disappears.

Adjustment of threshold values function sequence
By activating off-road mode:
- The thresholds for potential ESP intervention are widened i.e. ESP intervention only occurs under high vehicle dynamics.
- The ABS lockup phases are extended. For example, during a poor stretch of road the wheels are allowed to lock to reduce the braking distance (a loose surface supports a braking effect through a corresponding buildup of material in front of the front wheels).
- Ground with a low friction value is detected during ASR control.
The ASR activation thresholds are varied depending on the tire characteristics to improve traction.
The above-specified changes with respect to ESP, ABS and ASR are dependent on speed.
This means that the threshold values when off-road mode is active match those of on-road mode as of a speed of approx. v = 50 km/ h.
The thresholds again reach the off-road values for a renewed deceleration below a speed of approx. v = 50 km/h.

Function sequence for engine torque support
If braking torque can no longer be applied for at least one wheel (wheel is stationary because there is no load on it) with the downhill speed regulation activated, off-road mode activated and differential locks disengaged, brake pressure is built up actively at the wheels with traction via the Electronic Stability Program control unit.
Engine torque support is active up to a speed of v =18 km/h, coming from a lower speed.

Additional function requirements - dry braking
^ No brake intervention by a control system
^ Speed v > 30 km/h
^ Number of wiper cycles > 600

The wiper system (WSA) status is sent by the front SAM control unit with fuse and relay module over the chassis CAN to the ESP control unit.

Dry braking
The dry braking function enhances the performance capability of the front axle brake under wet 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.

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.

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 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 quickly pressing down hard on the brake pedal after coming to a standstill.
The adjusted brake pressure is maintained until the driver depresses the brake pedal again rapidly or starts off.

Warning strategy
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.

Function sequence for PRE-SAFE(R) system, PRE-SENSE
The PRE-SAFE(R) system, PRE-SENSE is activated in critical driving conditions, i.e. in a potential accident situation. The goal is to create the most favorable conditions possible for the occupants during the expected accident by activating the functions before the actual impact.

The PRE-SAFE(R) system, PRE-SENSE is integrated in the ESP control unit. If the ESP control unit detects one of the following situations, the PRE-SAFE(R) system, PRE-SENSE is activated:
- Panic post-braking (the driver's wish for deceleration is greater than physically possible)
- Severe oversteer (vehicle rear breaks away in combination with powerful ESP control intervention functions)
- Severe understeer (the vehicle pushes powerfully for a longer time over the front wheels)
- Rapid steering movements at higher speeds which suggest a shock reaction of the driver and can lead to vehicle instabilities

The PRE-SAFE(R) system, PRE-SENSE is described in a separate function description.

Switch ASR and ESP to passive (model 204.9, model 204.0/2 up to 28.2.10)
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 is read in over the instrument panel LIN (LIN 1) by the front SAM control unit with fuse and relay module and sent over chassis CAN to the ESP control unit. 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.

Switch ASR and ESP to passive (model 204.3 as of 1.6.10, model 204.0/2 as of 1.3.10)
The ASR and ESP functions in driving mode can be switched passive with left button group for multifunction steering wheel (S110) and right button group for multifunction steering wheel (S111) via the Assist menu and the ESP submenu of 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 transmits the request "ESP_OFF" over the chassis CAN to the ESP control unit.
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.

Failed Boost function sequence (with code (B03) ECO start/ stop function)
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.

Over Boost function sequence (with code (B03) ECO start/stop function)
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) reads in the status of the driver seat belt buckle and seat belt reminder warning switch and sends it over the chassis CAN to the ESP control unit.
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
- Electronic Stability Program warning lamp
- Messages in multifunction display
- Brake fluid and parking brake warning lamp (A1e7)

In the event of a failure of the ESP control unit a basic brake function without ABS is always available.

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.