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

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

General function requirements
^ "Circuit 61 ON" status

The "circuit 61 ON" status is sent by the CDI control unit (N3/9) (with diesel engine) or the ME-SFI [ME] control unit (N3/10) (with gasoline engine) to the chassis CAN (CAN E).

General
The Adaptive Brake (ABR) system assists the driver in dangerous situations which suddenly occur, and therefore contributes to active safety.

The Adaptive Brake system is an electrohydraulic brake system, which regulates the brake request for each wheel individually.

The following components are involved:

- Traction system hydraulic unit (A7/3)
- BAS brake booster (A7/7)
- Accelerator pedal sensor (B37)
- Yaw rate sensor for lateral and longitudinal acceleration (B24/15)
- Left front rpm sensor (L6/1)
- Right front rpm sensor (L6/2)
- Left rear rpm sensor (L6/3)
- Right rear rpm sensor (L6/4)
- Steering angle sensor (N49)
- ESP control unit (N47-5)
- Brake light switch (S9/1), model 221 as of CY 09 model refinement package

For vehicle test purposes the ABR system can be set to the dynamometer test mode, if the workshop menu is activated via the instrument cluster (A1) and the engine is then started. The vehicle dynamics control systems are switched passive. The ESP warning lamp (A1e41) and ABS indicator lamp (A1e17) in the instrument cluster light up. In addition, a message is displayed in the multifunction display (A1p13) of the instrument cluster. Roller dynamometer mode can also be activated via diagnosis.

The ABR system is comprised of the following partial functions:
^ Function sequence for Electronic Stability Program (ESP)
^ Function sequence for Electronic brake force distribution (EBD)
^ Function sequence for antilock brake system (ABS)
^ Function sequence for acceleration skid control (ASR)
^ Function sequence for Brake Assist (BAS) (except model 221 as of CY 09 model refinement package)
^ Function sequence for tire pressure loss warning (RDW) (except code (475) Tire pressure monitor (Premium))
^ Function sequence for speed-sensitive power steering (PML) (except model 221.022/054/056/070/071/080/084/086/087 and 221.122/154/156/170/171/180/184/186/187 as of CY 09 model refinement package)
^ Function sequence for HOLD function (starting-off aid)
^ Precharging function sequence
^ Dry braking function sequence
^ Function sequence for switching ASR and ESP to passive (model 216 up to CY 09 and model 221 up to CY 09 model refinement package)
^ Function sequence for switching ASR and ESP to passive (model 216 as of CY 09 and model 221 as of CY 09 model refinement package)
^ Function sequence for PRE-SAFE(R) system, PRE-SENSE (model 221 as of CY 09 model refinement package)
^ Hill Start Assist function sequence
^ Function sequence for Failed Boost (with engine 275 with code (Z07) Maximum protection)
^ Function sequence - Fading Brake Support
^ Function sequence for clearance reduction
^ Function sequence - Standstill coordinator
^ System fault display function sequence

Function sequence, ESP
ESP prevents breakaway when the vehicle oversteers or understeers. Within physical limits it ensures that the vehicle does not deviate from the course specified by the driver. 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 immediately carries out a self-test upon "circuit 15 ON". If there are no system errors, the ESP becomes operational and starts carrying out its functions.

Furthermore, the ESP control unit carries out system tests continuously during operation. Malfunctions and faults are stored in the fault memory.

To determine the vehicle handling the ESP control unit processes the following measured quantities:

- Yaw velocity and lateral acceleration recorded by the yaw rate sensor for lateral and longitudinal acceleration
- Steering wheel angle recorded by the steering angle sensor
- Brake pressure, recorded by left front pressure sensor (A7/3b3), right front pressure sensor (A7/3b4), left rear pressure sensor (A7/3b5), right rear pressure sensor (A7/3b6) (except model 221 as of CY 09 model refinement package) and from front axle brake pressure sensor (A7/3b1) in the hydraulic unit traction system
- Engine torque provided by CDI control unit or ME-SFI [ME] control unit
- Transmission shift stage, sent by the ETC [EGS] control unit (N15/3) (on transmission 722.6) or the fully integrated transmission control unit (VGS) (Y3/8n4) (on transmission 722.9) to the drive train CAN (CAN C) and forwarded by the central gateway control unit (N93) to the chassis CAN

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 of vehicle).

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 at the wheels are calculated from the engine torque, transmission shift stage and the brake pressure. If the yaw angle velocity measured does not match the specified value or if the determined side-slip angle is too large, the ESP control unit generates a signal for brake force build-up or reduction for the relevant wheel. The resulting forces stabilize the vehicle.

A distinction is made between the following interventions:
^ 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. This means that the vehicle pushes itself over the front axle and toward the outer edge of the corner. If at this point the driver depresses the accelerator pedal, the drive torque is first of all reduced. If this is not sufficient, brake pressure is built up at the rear wheel on the inside of the curve. 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.

To reduce the drive torque the ESP control unit transmits a signal via the chassis CAN to the CDI control unit or to motor electronics control unit which thereupon reduces the engine power accordingly.

A pending shift operation is suppressed for the duration of control intervention.

For this the ESP control unit transmits the "Downshift suppression" signal on the chassis CAN. The CDI control unit or the motor electronics control unit passes this on to the ETC [EGS] control unit or VGS control unit. The ETC [EGS] control unit or VGS control unit suppresses any imminent shift operation.

EBV function sequence
EBV assists the driver in the partial braking area. Overbraking of the rear axle is prevented. Vehicle stability is increased while braking in the curve, whilst if necessary the pressure at the rear wheel on the inside of the curve is reduced or at the front wheel on the outside of the curve is increased.

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 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 function sequence
ASR prevents the drive wheels from spinning while driving. In addition it causes improved driving stability for increased traction potential over the entire speed range.

ASR is comprised of the following partial functions:
^ Function sequence - drive torque control
^ Function sequence - brake torque control

Function sequence for drive torque control
The ESP control unit records the spinning of the drive wheels via the signals from the rpm sensors.

Wheel spinning is countered by reduction of the drive torque. For this the ESP control unit transmits a signal for drive torque reduction via the chassis CAN to the CDI control unit or to the motor electronics control unit which reduces the engine power accordingly.

The system constantly checks whether the drive torque specified by the driver via the accelerator pedal sensor can be allowed again e.g. due to improved road adhesion.

Function sequence - brake torque control
Selective interventions by the brake system at the spinning drive wheel means that the drive torque is transmitted to the opposite drive wheel which is running normally.

Function sequence for BAS (except model 221 as of CY 09 model refinement package)
BAS detects emergency braking situations based on rapid actuation of the brake pedal through the BAS membrane travel sensor (A7/7b1) and, if necessary, it increases the brake pressure through the BAS solenoid valve (A7/7y1), to achieve 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.

Function sequence for the tire pressure loss warning system (except code (475) Tire pressure monitor (Premium))
The tire pressure loss warning (RDW) system detects a significant pressure loss at a tire and then displays a warning message in the instrument cluster.

Operating principle of tire pressure loss warning system:
A dependence exists on tires between the rolling circumference and the tire internal pressure. This dependence is evaluated through relative comparison of the wheel speeds (LF+RR/RF+LR). The following ESP sensor signals are also included in the calculation, which are recorded by the yaw rate sensor for lateral and longitudinal acceleration:

- Lateral acceleration
- Turn rate
- Wheel torques

Function properties:

- Detection of significant pressure loss at a wheel.
- Active as from a minimum speed (v > approx. 15 km/h).
- Active for straight-ahead driving, lateral acceleration less than 1.5 m/s2.
- Active for uniform driving, longitudinal acceleration less than 1 m/s2.
- Inactive for control intervention functions (ABS, ASR, ESP).
- Inactive during large drive torque and under braking.
- Partially active with a low coefficient of friction, on rough roads, snow chains.
- The tire pressure loss warning (without details on position) occurs after several minutes driving. In the subsequent ignition sequences, a reminder message is displayed, provided that the system has not been reactivated.
- The tire pressure loss warning system has to be reactivated through the menu in the instrument cluster, after tire or wheels have been changed or the tire pressures have been changed. This erases any pending warning messages.
- After reactivation by the driver, the system automatically relearns the conditions. The learn mode takes roughly 10 minutes for each speed interval. There are 7 intervals. The system can still issue warnings during the learn mode (and the immediately adjacent) intervals.
- Uniform pressure loss at all 4 wheels (e.g. due to diffusion) cannot be detected.
- Incorrect operation by the driver cannot be detected (e.g. reactivation despite significant pressure reduction).

Function sequence for speed-sensitive power steering (PML) (except model 221.022/054/056/070/071/080/084/086/087 and 221.122/154/156/170/171/180/184/186/187 as of CY 09 model refinement package)
The task of speed-sensitive power steering is to match the level of steering assistance to the vehicle speed. This is done using a current-controlled speed-sensitive power steering solenoid valve (Y10) on the steering gear, which is actuated by the ESP control unit. A high level of steering assistance is provided at a low speed, while at high speeds the level of steering assistance is reduced. The vehicle speed signal is received by the ESP control unit over the chassis CAN from the instrument cluster.

Additional function requirements for HOLD function (starting-off aid)
^ Transmission selector lever not in position "P"
^ Vehicle not secured with parking brake
^ Incline detected with vehicle at standstill

Function sequence for HOLD function (starting-off aid)
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 activation of the HOLD function is displayed to the driver in the form of a "HOLD" message in the instrument cluster.

The adjusted brake pressure is held until the driver again presses with a certain pressure on the brake pedal or starts off.

The intelligent servo module for DIRECT SELECT (A80) transmits the transmission selector lever position on the drive train CAN. The CDI control unit or ME-SFI [ME] control unit forward this status to the ESP control unit via the chassis CAN.

The electric parking brake controller unit (A13) transmits the status of the parking brake on the front end CAN (CAN G). The central gateway control unit forwards this status to the ESP control unit via the chassis CAN.

The yaw rate sensor for lateral and longitudinal acceleration transmits information on a detected incline to the ESP control unit via the vehicle dynamics CAN (CAN H).

Furthermore, the HOLD function will be deactivated automatically under the following conditions:

- Operation of parking brake
- Change of transmission selector lever position into position "P"

Under the following conditions the HOLD function is switched off automatically before the driver leaves the vehicle:

- Open driver door at "circuit 15 ON" and seat belt buckle not fitted (message in multifunction display)

The "circuit 15 ON" status is sent by the EIS [EZS] control unit (N73) to the chassis CAN.

On model 216 the status of the driver door is defined via the status of the left rotary tumbler switch (A85s1) which is read in by the left door control unit (N69/1).

The status of the driver door is defined on model 221 by the left front rotary tumbler switch (A85s1), which is read in by the left front door control unit (N69/1).

The status of the driver door is sent in each case over the interior CAN (CAN B). The central gateway control unit forwards this status to the ESP control unit via the chassis CAN.

Additional function requirements - precharging
^ No active control intervention function by ABS, ASR or ESP
^ ESP system not switched passive

Precharging function sequence
The precharging function applies the brake pads to the brake disks in the event of a supposed emergency braking situation being detected

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 therefore contributes to the reduction in braking distance.

Emergency braking detection takes place via the release gradient of the accelerator pedal sensor, which is formed from the Controller Area Network (data bus/CAN Bus) (CAN) signal "accelerator pedal position".

If a rapid release of the accelerator pedal is detected, the system assumes that the driver intends to brake. The precharging function is activated and a brake pressure of p = 3 to 4 bar requested.

Additional function requirements - dry braking
^ No active control intervention function by ABS, ASR or ESP
^ Windshield wiper active

The front SAM control unit with fuse and relay module (N10/1) transmits the status "windshield wiper active" on the interior CAN. The central gateway control unit forwards this status to the ESP control unit via the chassis CAN.

Dry braking function sequence
Dry braking assists the performance capability of the front axle brake under wet conditions. The water film is wiped off the brake disk by cyclically applying the brake pads for t = 0.5 s with a brake pressure p < 1 bar.

This improves the response time of the brake.

Function sequence for switching ASR and ESP to passive (model 216 up to CY 09 and model 221 up to CY 09 model refinement package)
The ASR and ESP functions can be switched passive by operating the ESP OFF switch (S6/2s11) in the cockpit switch group (S6/2). The upper control panel control unit (N72/1) reads in the status of the ESP OFF switch via the instrument panel LIN (LIN 1) and transmits this status to the interior CAN. The central gateway control unit forwards this status to the ESP control unit via the chassis CAN. 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.

Function sequence for switching ASR and ESP to passive (model 216 as of CY 09 and model 221 as of CY 09 model refinement package)
The ASR and ESP functions can be switched to passive while automotive operation using the left button group (S110) and the right multifunction steering wheel button group (S111) through the Assist menu and the ESP submenu in the instrument cluster. The multifunction steering wheel's (MFL) control signals are received by the instrument cluster as follows:

- Steering LIN (LIN E1)
- Steering column tube module (N80)
- Chassis CAN
- Central gateway control unit
- Central CAN (CAN F)

The instrument cluster then sends the "ESP_OFF" request to the central gateway control unit. The central gateway control unit passes this on to the ESP control unit via the chassis CAN.

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.

Function sequence for PRE-SAFE(R) system, PRE-SENSE (model 221 as of CY 09 model refinement package)
The PRE-SAFE(R) system, PRE-SENSE is activated in critical driving states, 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 into 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 (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.

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 Start Assist function sequence
When starting off Hill Start Assist prevents the vehicle rolling back opposite to the gear range engaged during the time it takes for the driver to move his/her foot 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.

The data from the yaw rate sensor for lateral and longitudinal acceleration is read in by the ESP control unit via the vehicle dynamics CAN. For this the brake pressure applied by the driver is maintained by the traction system hydraulic unit for a period of t = 0.8 to 1.5 s and switched off by a sufficiently large starting off torque.

The intelligent servo module for DIRECT SELECT () transmits the transmission selector lever position on the drive train CAN. The CDI control unit or ME-SFI [ME] control unit forwards this status to the ESP control unit via the chassis CAN.

The electric parking brake controller unit () transmits the status of the parking brake on the front end CAN.

The central gateway control unit forwards this status to the ESP control unit via the chassis CAN.

Function sequence for Failed Boost (with engine 275 with code (Z07) Maximum protection)
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 front axle brake pressure sensor detects that the BAS brake booster is not assisting the driver as required, then actuation of the high pressure and return flow pump (A7/3m1) enables Failed Boost to assists the driver. Hydraulic boosting occurs with a suitable boost factor.

Function sequence - Fading Brake Support
The Fading Brake Support function assists the driver when the brakes overheat and thus the brake force decreases.

With extreme overheating a message is output via the multifunction display.

The fading brake support function serves to provide additional driver assistance when the brake system is hot in order to achieve the best possible deceleration in this operating case as well. In the event of extreme overheating, the driver may be additionally notified by a message on the instrument cluster's multifunction display.

The sensing of overheating (fading) is based on a brake disk temperature model. If a specific threshold is exceeded, fading is assumed, fading brake support becomes active. In addition this function can also be activated by the comparison of the brake pressure level with the actual deceleration or by the direct request through the antilock brake system (ABS).

Function sequence for clearance reduction
The clearance reduction function applies the brake pads to the brake disks on the front axle when dynamic cornering (evaluation of yaw velocity by yaw rate sensor for lateral and longitudinal acceleration). Consequently the clearance between the brake pad and brake disk is compensated in order to receive the required braking power at the corresponding wheel as quickly as possible in the event of any ESP intervention by the brake system.

Function sequence - standstill coordinator
If the assistance systems are activated such as, e.g. the HOLD function and the driver status is unclear, the standstill coordinator requests the change over of the vehicle into a secured condition.

Driver status is deemed to be unclear when the driver door is open and the belt tongue of the driver seat belt is not plugged into the seat belt buckle. The plugging in of the seat belt tongue into the seat belt buckle is detected by the driver seat belt buckle switch and seat belt reminder warning switch (S68/1). The restraint systems control unit (N2/7) reads in the status of the driver seat belt buckle switch and seat belt reminder warning switch directly and transmits this to the ESP control unit via the chassis CAN. The support systems cannot be operated.

System fault display function sequence
The ESP control unit carries out system tests continuously while driving. If malfunctions or faults are detected, the ESP control unit transmits corresponding information on the chassis CAN. The central gateway control unit passes these on to the instrument cluster via the central CAN.

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

- ABS indicator lamp
- ESP warning lamp
- Messages in the multifunction display in the instrument cluster

In order to avoid malfunction due to too low fill level of brake fluid, the brake fluid control switch (S11) monitors the fill level in the brake fluid reservoir. The status of the brake fluid control switch is read in directly by the front SAM control unit and provided on the interior CAN. The central gateway control unit passes this on to the ESP control unit via the chassis CAN. A basic brake function is always available in the event of failure of the ESP control unit.