GF42.47-P-0001RIT Adaptive Brake (ABR), Function
GF42.47-P-0001RIT Adaptive brake (ABR), function
MODEL 230.479 with CODE (P99) Special model "AMG Black Series"
Function requirements, general
^ Status "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.
The ESP, SPS [PML] and BAS control unit (N47-5) evaluates the data from the following components to record the current driving situation:
- Yaw rate and lateral acceleration sensor (B24/15) via sensor CAN (CAN H)
- Accelerator pedal sensor (B37)
- 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) via steering column tube module (N80) and engine compartment CAN (CAN C)
- Brake light switch (S9/1)
The system is made up of the following component functions:
^ Electronic Stability Program (ESP)
^ Electronic brake force distribution (EBV)
^ Anti lock brake system (ABS)
^ Acceleration skid control (ASR), electronic traction system (ETS)
^ Brake Assist (BAS)
^ Precharging, depending on accelerator pedal actuation
^ Precharging, depending on lateral acceleration
^ ASR and ESP ON, Sport or OFF
^ System fault display
^ Fault handling function sequence
ESP
ESP prevents the vehicle from breaking away when over steering or under steering. 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, SPS [PML] and BAS control unit processes the following measured quantities to determine the vehicle behavior:
- yaw velocity
- steering wheel angle
- Brake pressure
- Engine torque
- Transmission shift stage
- Lateral acceleration
Differentiation is made between the following control intervention functions:
^ 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 accelerator pedal is pressed at this time, the ESP system will first of all reduce the drive torque.
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 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, SPS [PML] and BAS control unit transmits via engine compartment CAN a signal for drive torque reduction to the ME-SFI [ME] control unit (N3/10) which reduces the engine output accordingly.
A pending shift operation is suppressed for the duration of control intervention.
To suppress shift operation, the ESP, SPS [PML] and BAS control unit sends a signal via engine compartment CAN to the ETC [EGS] control unit (N15/3). The ETC [EGS] control unit then suppresses the shift operation.
EBD (Electronic brake force distribution)
EBD [EBV] provides assistance when the driver applies medium force to the brake pedal. It prevents over braking of the rear axle and increases vehicle stability when braking in the 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 yaw velocity measured does not match the specified value or if the determined side-slip angle is too large, the ESP, SPS [PML] and BAS control unit generates a signal for brake force build-up or reduction for the relevant wheel. The resulting forces stabilize the vehicle.
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, SPS [PML] and BAS 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.
The ESP, SPS [PML] and BAS 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. The ESP, SPS [PML] and BAS control unit transmits via engine compartment CAN a signal for drive torque reduction to the ME-SFI [ME] control unit, which reduces the engine output 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. The drive torque is transmitted to the opposite, turning 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. For this the ESP, SPS [PML] and BAS control unit evaluates the degree of pressure rise in the brake system and initiates an emergency stop in the event that a certain triggering threshold is exceeded.
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" signal. If a rapid release of the accelerator pedal is detected, the system assumes that the driver intends to brake. recharging is activated and a brake pressure of 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.
ASR and ESP ON, Sport or OFF
ESP can be operated in 3 different operating modes. Switching between the operating modes is done by pressing the ESP OFF switch (N72s14) in the lower control panel control unit (N72). To switch between ESP ON and ESP Sport mode, press the ESP OFF switch only briefly. To switch off ESP, press and hold the ESP OFF switch for t > 2.5.
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 ESP and ABS warning lamp (A1e41) and the ESP OFF indicator lamp (A1e30) in the instrument cluster (A1) are unlit; the ESP and ABS warning lamp flashes during ESP intervention.
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 ESP and ABS warning lamp in the instrument cluster is permanently 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 ESP and ABS warning lamp and the ESP OFF indicator lamp in the instrument cluster are permanently lit. The message "ESP OFF" appears in the instrument cluster.
All Pre-Safe functions are deactivated in ESP OFF mode.
System fault display
The driver is informed about the system status and about faults by the following displays:
- ABS indicator lamp (A1e17)
- ESP and ABS warning lamp
- Messages in the instrument cluster
In the event of failure of the ESP, SPS [PML] and BAS control unit, a basic brake function without ABS is always available.
The status of the parking brake indicator switch (S12) is read in by the driver-side SAM control unit (N10/10) and sent via the interior CAN (CAN B) to the instrument cluster.
The actuation of function messages is carried out exclusively by the ESP, SPS [PML] and BAS control unit.
Warning messages are actuated independently by the ESP, SPS [PML] and BAS control unit or by the instrument cluster depending on the event. The driver is informed immediately about the system status or about faults.
Fault handling function sequence
The range of functions can vary depending on the received signals.
The following table shows function deactivation owing to a component failure or defect.
