Function Description

VEHICLE DYNAMICS CONTROL (VDC) 

• VDC 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 processes the following measured quantities to determine the vehicle behavior:
  • Yaw velocity
  • Steering angle
  • Brake pressure
  • Engine torque
  • Transmission stage
  • Lateral acceleration
  • Wheel speed
• Differentiation is made between the following intervention types:

  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:
  • 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 electronic stability program control unit sends a signal to reduce the drive torque over the CAN communication to the ECM, which then reduces the engine power accordingly.
• A pending shift operation is suppressed for the duration of control intervention.
• To do so, the electronic stability program control unit sends a signal over the CAN communication to the ECM, which forwards the information over the CAN communication to the TCM. The latter control unit suppresses the shift operation.

STANDSTILL CONTROL (SSC) 

• The standstill control monitors the braking driver assistance systems ICC and HOLD function below a speed of 3 km/h (1.8 MPH) until the vehicle has come to a safe standstill. Within this vehicle speed range, the SSC is responsible for 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 SSC is requested by the driver assistance systems.
• If vehicle rolling is detected, the brake pressure is increased until the vehicle is stationary again. In the case of vehicles equipped with adaptive brake system (with ICC), a leakage compensation is also active during the safe standstill.
• If the brake pressure measured by means of the circuit pressure sensors drops relative to the specified pressure request of the SSC, the specified pressure of the SSC is restored by means of an active pressure buildup.
• Securing the vehicle by means of the SSC is necessary if the following events occur:
  • Driver is detected as absent (the driver door is open and the driver belt buckle is not fastened)
  • Engine OFF, unless the engine has been switched off by the ECO start/stop function
  • Undervoltage and overvoltage in on-board electrical system
  • Request relevant to vehicle safety (e.g. ICC)
  • CAN communication and VDC malfunction that lead to a temporary deactivation
  • SSC monitoring events that result in temporary or permanent deactivation
  • Defined hydraulic hold period of 10 min has expired

Door contact plausibility check

• The plausibility check detects any malfunction along the signal path from the left front door rotary tumbler switch or the right front door rotary tumbler switch (depending on the global country coding for right-hand and left-hand drive vehicle), read in by the left front door control unit or right front door control unit and over the CAN communication with the electronic ignition switch control unit interface to the electronic stability program control unit.
• If, as the result of an electrical or mechanical malfunction, "Driver door closed" is detected by mistake although the driver door is open, this is detected by the door contact plausibility check in the SSC and a corresponding malfunction is stored in the electronic stability program control unit.

SSC deactivation

• Deactivation of the SSC is signaled internally in the electronic stability program control unit and externally over the CAN communication.
• Activation of the driver assistance systems is no longer possible. Securing of the vehicle is additionally requested immediately if the SSC is deactivated and a driver assistance system is active.

Sliding

• When the vehicle is stationary, the SSC 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.

Securing vehicle

• The vehicle is secured by the comfort securing system of the electric parking brake, which is prompted to lock by the SSC.
• For this purpose, the electronic stability program control unit sends a signal via the CAN communication to the electric parking brake control unit.
• The vehicle is secured after the locking request has been implemented and the feedback signal to confirm that the service brake is applied has been sent from the electric parking brake control unit to the electronic stability program control unit.
• The existing brake pressure at the wheels is reduced and the SSC becomes inactive.
• If the close request is not implemented by the electric parking brake within a defined time or the electric parking brake signals a system malfunction to the SSC, the electric parking brake is detected as being malfunction and the safety strategy becomes active.

ELECTRONIC BRAKE FORCE DISTRIBUTION (EBD) 

• EBD provides assistance when the driver applies medium force to the brake pedal.
• EBD 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 if the determined side slip angle is too large, the electronic stability program control unit generates a signal for brake force buildup or reduction for the relevant wheel.
• The resulting forces stabilize the vehicle.

EMISSION TEST, ROLLER DYNAMOMETER MODE 

• For vehicle test purposes, the adaptive brake can be set to dynamometer test mode if the workshop menu is activated via the combination meter and the engine is then started.
• VDC, ABS and ASR are then switched to passive.
• The VDC warning lamp and the ABS warning lamp in the combination meter turn ON.
• In addition, a message is displayed in the information display of the combination meter.

ANTI-LOCKING SYSTEM (ABS) 

• ABS prevents the wheels locking when braking and as a result maintains the steerability and directional stability and road adhesion during the vehicle deceleration.
• If a locking wheel is detected by the electronic stability program control unit on the basis of the signals from the axle rpm sensors, the brake pressure is reduced at the appropriate wheel until the wheel begins to turn again.

ACCELERATION SKID CONTROL (ASR), TRACTION CONTROL SYSTEM (TCS) 

• ASR and TCS prevent the tire from spinning when driving.
• ASR and TCS also serve to provide improved directional stability and road adhesion for increased traction potential over the entire vehicle speed range.
• Spinning of the tire is detected by the electronic stability program control unit using the signals from the axle rpm sensors.
• Wheel spinning is countered by reduction of the drive torque.
• For this purpose, the electronic stability program control unit sends a signal requesting a reduction in drive torque via the CAN communication to the ECM which then 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.

BRAKE ASSIST SYSTEM (BAS) (WITHOUT ICC) 

• 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 purpose, the electronic stability program control unit evaluates the increase in pressure in the brake system and initiates an emergency stop if a certain triggering threshold is exceeded.

BRAKE ASSIST SYSTEM PLUS (BAS PLUS) (WITH ICC) 

• BAS Plus increases the brake pressure depending on the speed of the brake pedal operation and the distance of the vehicle driving in front.

HILL START ASSIST 

• Additional function requirements for the hill start assist
  • Vehicle not secured with electric parking brake
  • Incline detected with vehicle at standstill
• 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 released automatically if, when the vehicle is stationary, an uphill or downhill gradient which would cause the vehicle to roll opposite the travel direction of the engaged gear range is detected by the electronic stability program control unit.
• The electronic stability program control unit also directly reads in the brake lights switch signal and thereby detects the status of the brake pedal.
• The electric parking brake control unit sends the status of the electric parking brake via the CAN communication to the electronic stability program control unit.
• The brake pressure applied by the driver is maintained in the brake system by the traction system hydraulic unit.
• Following release of the brake pedal and detection of a start-off request, reduction of the brake pressure is controlled by means of torque balancing system.
• This system takes into consideration the incline output torque, the total braking torque and the available drive torque.
• When the start-off torque is high enough, the hill start assist is deactivated and the vehicle starts off without rolling in the undesired direction of travel.
• If the driver does not depress the brake pedal, the pressure in the brake system is reduced after 1 second.
• The hill start assist is terminated immediately if:
  • The engine is switched off, unless the engine is switched off by the ECO start/stop function.
  • The driver terminates the pulling away procedure by fully releasing the accelerator pedal.
  • A forward/reverse gear change is performed.
  • On vehicles with automatic transmission a gear change is made the target parking position. to selector lever position "N".
  • The electric parking brake is applied.
  • The vehicle is slipping.
• The hill start assist does not function, if:
  • The vehicle is driven off on a level road or on a downhill gradient.
  • On vehicles with automatic transmission the transmission is in selector lever position "N".
  • The electric parking brake is applied.
  • VDC is malfunctioning.
  • The vehicle is slipping.

DRY BRAKING 

• Additional function requirements dry braking:
  • No brake intervention by a driver assistance system
  • Speed: 50 km/h (31 MPH) or more
  • Windshield wiper system switched on
• The status of the windshield wiper system is sent by the BCM over the CAN communication with the interface for the electronic ignition switch control unit to the electronic stability program control unit.
• The dry braking function enhances the performance of the brakes in wet driving conditions. The brake pads are applied cyclically for 1 second with a brake pressure of approx. 150 kPa (1.5 bar, 1.5 kg/cm ² , 22 psi) to remove the film of water from the brake disk rotor. 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 disk rotors.
• 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 is achieved.
• Emergency braking is detected on the basis of the release gradient of the accelerator pedal.
• 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 approx. 200 kPa (2 bar, 2 kg/cm ² , 29 psi) 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 disk rotors.
• This closes the air gap between the brake pad and brake disk rotor in order to achieve the required braking power at the corresponding wheel as quickly as possible in the event of VDC intervention by the brake system.

EXTENDED TRACTION CONTROL 

• The extended traction control function reduces the tendency of the vehicle to understeer during acceleration after fast cornering.
• This is achieved by a braking torque being applied to the inner front wheel.
• If a maximum braking torque for the front wheel is reached or the front wheel slips as a result of the applied braking torque, the calculated excess braking torque is fed to the inner rear wheel.
• The desired vehicle yawing moment which the driver specifies by means of the steering angle is thus achieved.
• Benefits of extended traction control:
  • The engine torque remains in the upper range
  • The vehicle speed can increase during cornering
  • The steering wheel angle requirement is considerably less and smoother

HOLD FUNCTION 

• The HOLD function assists the driver during waiting times in traffic or 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 combination meter.
• The HOLD function can be activated if:
  • The vehicle is stationary
  • The seat belt is fastened or the driver door is closed.
  • On vehicles with automatic transmission, the selector lever is not in position "P".
  • The engine is running or has been switched off by the ECO start/stop function.
  • ICC is not active.
  • The electric parking brake is not applied or it is in the process of being applied.
  • There is no shutoff in the standstill control.
  • The vehicle is not sliding.
• If the driver releases the brake pedal, an incline-dependent hold pressure is set and maintained until the driver quickly depresses the brake pedal again or drives off.
• Pressure reduction when starting off is performed by the standstill control depending on the respective situation.
• The HOLD function is deactivated automatically if:
  • The accelerator pedal is depressed (except with automatic transmission in position "N").
  • On vehicles with automatic transmission, the selector lever is in position "P".
  • The brake pedal is depressed again with a certain pressure until the "HOLD" status line disappears in the combination meter.
  • The electric parking brake is applied.
  • ICC is activated.
  • The brake pedal is depressed and the vehicle is sliding.
• If the HOLD function is activated and the driver wants to leave the vehicle, removal of the ignition key from the electronic ignition switch control unit is prevented.
• An acoustic and warning buzzer will be issued through the combination meter.

STEER ASSIST 

• Steer assist is intended to help the driver achieve the optimal steering characteristics in critical situations.
• Steer assist is provided with the aid of the electric power steering control unit and electronic stability program control unit.
• The following functions are performed here:
  • Driver support or stabilization through countersteering of a vehicle with oversteer
  • Driver support for braking on varying road surfaces
• The current vehicle status is sensed by the electronic stability program control unit.
• When required, the "Steer Assist request" is sent over the CAN communication with the interface for the electronic ignition switch control unit to the EPS control unit.
• The EPS control unit actuates the EPS actuator correspondingly.
• With semi-automatic parking space entry and semi-automatic parking space exit, the electronic stability program control unit receives the required braking torque from the sonar control unit over the CAN communication and actuates the traction system hydraulic unit directly. The vehicle is braked. The vehicle is braked to stop at the required maneuvering points as well as an in the target parking position.

SYSTEM MALFUNCTION DISPLAY FUNCTION 

• The driver is informed about the system status and about malfunction by the following displays:
  • ABS warning lamp
  • Brake warning lamp
  • VDC warning lamp
  • Messages in information display
  • If the electronic stability program control unit malfunction, basic braking without ABS is always available.
  • The status of the brake fluid level switch is read in by the BCM and sent via the CAN communication to the combination meter.